Technical Support Document for
Endangerment and Cause or
   Contribute Findings for
  Greenhouse Gases under
    Section 202(a) of the
        Clean Air Act
             April 17, 2009
 Climate Change Division, Office of Atmospheric Programs
      U.S. Environmental Protection Agency
            Washington, DC

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Acknowledgments


EPA authors and contributors:

Benjamin DeAngelo, Jason Samenow, Jeremy Martinich, Doug Grano, Dina Kruger, Marcus Sarofim,
William Perkins, Melissa Weitz, Leif Hockstad, William Irving, Lisa Hanle, Darrell Winner, David
Chalmers, Chris Weaver, Susan Julius, Brooke Hemming, Sarah Garman, Rona Birnbaum, Paul
Argyropoulos, Ann Wolverton, Al McGartland, Alan Carlin, John Davidson, Tim Benner, Carol Holmes,
John Hannon, Jim Ketcham-Colwill, Andy Miller, Pamela Williams


Federal expert reviewers

Virginia Burkett, USGS; Phil DeCola; NASA (on detail to OSTP); William Emanuel, NASA; Anne
Grambsch, EPA; Jerry Hatfield, USDA; Anthony Janetos; DOE Pacific Northwest National Laboratory;
Linda Joyce, USDA Forest Service; Thomas Karl, NOAA; Michael McGeehin, CDC; Gavin Schmidt,
NASA; Susan Solomon, NOAA; Thomas Wilbanks, DOE Oak Ridge National Laboratory
Other contributors:
Christine Teter, independent contractor for Stratus Consulting and Joel Smith, Stratus Consulting, assisted
with editing and formatting.
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Table of Contents

Executive Summary	ES-1

I.   Introduction

    1.  Introduction and Background 	1
       a.   Scope and approach of this document	1
       b.   Data and scientific findings considered by EPA	3
       c.   Roadmap for this document	7

II.   Greenhouse Gas Emissions

    2.  Greenhouse Gas Emissions and Atmospheric Concentrations 	9
       a.   U.S. and global greenhouse gas emissions	9
       b.   Historic & current global greenhouse gas concentrations	13

III.  Global and U.S. Observed and Projected Effects from Elevated Greenhouse Gas
    Concentrations

    3.  Direct Effects of Elevated Greenhouse Gas Concentrations	17

    4.  Radiative Forcing and Observed Climate Change	19
       a.   Radiative forcing due to greenhouse gases and other factors	19
       b.   Global changes in temperature	22
       c.   U.S. changes in temperature	27
       d.   Global changes in precipitation	28
       e.   U.S. changes in precipitation	29
       f   Global sea level rise	30
       g.   U.S. sea level rise	31
       h.   Global ocean acidification	31
       i.   Global changes in physical and biological systems	31
       j.   U.S. changes in physical and biological systems	34
       k.   Global extreme events	35
       1.   U.S. extreme events	36

    5.  Attribution of Observed Climate Change to Anthropogenic Greenhouse Gas Emissions at
       the Global and Continental Scale	39
       a.   Attribution of observed climate change to anthropogenic emissions	39
       b.   Attribution of observed changes in physical & biological systems	43

    6.  Projected Future Greenhouse Gas Concentrations and Climate Change	45
       a.   Global emission scenarios and associated changes in concentrations and radiative forcing... 45
       b.   Projected changes in global temperature, precipitation patterns, sea level rise, and ocean
           acidification	52
       c.   Projected changes in U.S. temperature, precipitation patterns, sea level rise	57
       d.   Cryosphere (Snow and Ice) projections, focusing on North America and the U.S	60
       e.   Extreme events projections, focusing on North America and the U.S	61
       f.   Abrupt climate change and high impact events	63
       g.   Effects on/from stratospheric ozone	66
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       h.   Land use and land cover change	67

IV.  U.S. Observed and Projected Human Health and Welfare Effects from Climate Change

    7   Human Health	69
       a.   Temperature effects	69
       b.   Extreme events	71
       c.   Climate-sensitive diseases	72
       d.   Aeroallergens	73

    8   Air Quality	75
       a.   Tropospheric ozone	75
       b.   Particulate matter	79
       c.   Health Effects due to CO2-Induced Increases in Tropospheric O3 and Particulate Matter	81

    9.  Food Production and Agriculture	82
       a.   Crop yields and productivity	83
       b.   Irrigation requirements	85
       c.   Climate variability and extreme events	85
       d.   Pests and weeds	86
       e.   Livestock	87
       f   Freshwater and marine fisheries	87

    10. Forestry	89
       a.   Forest productivity 	89
       b.   Wildfire and drought risk	91
       c.   Forest composition	92
       d.   Insects and diseases	93

    11. Water Resources	94
       a.   Water supply	94
       b.   Water quality	97
       c.   Extreme events	98
       d.   Implications for water uses	99

    12. Sea Level Rise and Coastal Areas	100
       a.   Vulnerable areas 	100
       b.   Extreme events	103

    13. Energy, Infrastructure and Settlements	105
       a.   Heating and cooling requirements	105
       b.   Energy production	106
       c.   Infrastructure and settlements	108

    14. Ecosystems and Wildlife	113
       a.   Ecosystems and species	113
       b.   Ecosystem services	120
       c.   Extreme events	120
       d.   Implications for tribes	120
       e.   Implications for tourism	121
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V. International Observed and Projected Human Health and Welfare Effects from Climate
   Change

   15. International Impacts	123
      a.  National security	123
      b.  Overview of international impacts	125

References	129

Appendix A on Adaptation	140

Appendix B on Greenhouse Gas Emissions from Section 202 Source Categories	144

Appendix C on Direct Effects of Greenhouse Gases on Human Health	157

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Executive Summary

This document provides technical support for the endangerment analysis concerning greenhouse gas
(GHG) emissions that may be addressed under the  Clean Air Act.  This document itself does not convey
any judgment or conclusion regarding the question of whether GHGs may be reasonably anticipated to
endanger public health or welfare, as this decision is ultimately left to the judgment of the Administrator.
The  conclusions here  and the information throughout this  document are primarily drawn  from the
assessment reports of  the Intergovernmental Panel on Climate Change and the U.S. Climate Change
Science Program.

Observed Trends in Greenhouse Gas Emissions and Concentrations

Greenhouse gases, once emitted, can remain in  the atmosphere for  decades to centuries, meaning
that 1) their concentrations  become well-mixed throughout the global atmosphere  regardless of
emission origin, and  2)  their effects on climate are long lasting.  The primary long-lived GHGs
directly emitted by human activities include carbon dioxide (CO2), methane (CHO, nitrous oxide (N2O),
hydrofluorocarbons (HFCs), perfluorocarbons (PFCs)  and  sulfur hexafluoride (SF6).  Greenhouse gases
have a warming effect by trapping heat in the atmosphere that would otherwise escape to space.

In 2006,  U.S. GHG emissions were 7,054 teragrams1 of CO2 equivalent2 (TgCO2eq). The dominant
gas emitted is CO2, mostly from fossil fuel combustion.  Methane is the  second largest component of
U.S. emissions, followed by  N2O, and  the fluorinated  gases (HFCs, PFCs, and SF6).   Electricity
generation is the largest emitting sector (34% of total  U.S. GHG emissions), followed by transportation
(28%) and industry (19%).

Transportation sources under section 202 of the Clean  Air Act (passenger cars, light duty trucks,
other trucks and buses,  motorcycles, and cooling) emitted 1,665 TgCO2eq in 2006, representing
almost 24% of total U.S.  GHG emissions.

U.S. transportation sources under section 202 made up 4.3% of total global GHG emissions in 2005,
which, in addition to the U.S. as a whole, ranked only behind total GHG emissions  from  China, Russia
and India but ahead of Japan, Brazil, Germany and the rest of the world's countries.  In 2005, total U.S.
GHG emissions were responsible for  18% of global emissions, ranking only behind China, which was
responsible for 19% of global GHG emissions.

The global atmospheric CO2 concentration has  increased about 38% from pre-industrial levels to
2009, and  almost all  of  the increase is due  to  anthropogenic emissions.  The  global atmospheric
concentration of CFU has increased by 149% since pre-industrial levels (through 2007); and the N2O
concentration has increased 23% (through 2007). The  observed concentration increase in these gases can
also  be attributed primarily to anthropogenic emissions. The industrial  fluorinated gases, HFCs, PFCs,
and SF6, have relatively low atmospheric concentrations but are increasing rapidly; these gases are almost
entirely anthropogenic in origin.

Historic  data show that  current atmospheric concentrations of the two most important directly
emitted,  long-lived GHGs (CO2 and CH4)  are well  above the natural range  of atmospheric
1 One teragram (Tg) = 1 million metric tons. 1 metric ton = 1,000 kg = 1.102 short tons = 2,205 Ibs.
2 Long-lived GHGs are compared and summed together on a CO2 equivalent basis by multiplying each gas by its
Global Warming Potential (GWPs), as estimated by IPCC. In accordance with UNFCCC reporting procedures, the
U.S. quantifies GHG emissions using the 100-year time frame values for GWPs established in the IPCC Second
Assessment Report.
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concentrations compared to the last 650,000 years.  Atmospheric  GHG concentrations have been
increasing because anthropogenic emissions have been outpacing the rate at which GHGs are removed
from the atmosphere by natural processes over timescales of decades to centuries.

Observed Effects Associated with Global Elevated Concentrations of GHGs

Current  ambient air concentrations of CO2  and other GHGs remain well below published exposure
thresholds for any direct adverse health effects, such as respiratory or toxic effects.

The global average net effect of the increase in atmospheric GHG concentrations, plus other human
activities (e.g., land use change and aerosol  emissions), on the global energy balance since 1750 has
been one of warming.  This total net heating effect, referred to as forcing, is estimated to be +1.6 (+0.6 to
+2.4) Watts per  square meter (W/m2),  with  much of the range surrounding this estimate due  to
uncertainties about the cooling and warming effects of aerosols. The combined radiative forcing due to
the cumulative (i.e.,  1750  to 2005)  increase  in atmospheric concentrations  of CO2, CH4, and N2O is
estimated to  be +2.30 (+2.07 to +2.53) W/m2.  The rate of increase in positive radiative forcing due to
these three GHGs during the industrial era is very likely to have been unprecedented in more than 10,000
years.

Warming of the climate system  is unequivocal, as is now evident from observations of increases in
global average air and ocean temperatures, widespread melting of snow and ice, and rising global
average sea level. Global mean  surface  temperatures have risen by 0.74°C  (1.3°F)  (±0.18°C) over the
last 100 years.  Eight of the ten  warmest years on record have occurred since 2001. Global mean surface
temperature  was higher during the last few decades of the 20th century than during any comparable
period during the preceding four centuries.

Most of the observed  increase in global average temperatures since the  mid-20th century is very
likely  due  to the observed  increase  in anthropogenic  GHG concentrations.   Climate  model
simulations suggest natural forcing alone  (e.g., changes in solar irradiance) cannot explain the observed
warming.

U.S. temperatures also warmed during the 20th and into the 21st century;  temperatures are now
approximately  0.7°C (1.3°F) warmer than  at the start of the 20th century, with an increased rate  of
warming  over the past 30  years.  Both the IPCC and CCSP reports attributed recent North American
warming  to elevated GHG concentrations.  In the CCSP (2008g) report the authors  find that for North
America, "more than half of this warming [for the period 1951-2006] is likely the result of human-caused
greenhouse gas forcing of climate  change."

Observations  show that changes are occurring  in the amount, intensity,  frequency and  type  of
precipitation.  Over the contiguous U.S., total annual precipitation increased by 6.5% from  1901-2006.
It is likely that there have been increases in the number of heavy precipitation  events within many land
regions, even in those where there has been a reduction in total precipitation amount, consistent with a
warming  climate.

There is  strong  evidence that global sea level gradually rose in the 20th century and is currently
rising at  an  increased  rate.  It is not clear whether the increasing rate of sea level rise is a reflection of
short-term variability or an increase in the longer-term trend. Nearly all of the Atlantic Ocean shows sea
level rise during  the last 50 years with the rate  of rise reaching a maximum  (over 2 mm per year) in a
band along the  U.S. east coast running east-northeast.
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Satellite data since 1978 show that annual average Arctic sea ice extent has shrunk by 2.7 ± 0.6% per
decade, with larger decreases in summer of 7.4 ± 2.4% per decade.

Widespread changes in extreme temperatures have been observed in the last 50 years  across all
world regions including the U.S.  Cold days, cold nights, and frost have become less frequent, while hot
days, hot nights, and heat waves have become more frequent.

Observational evidence from all  continents and most oceans shows that many natural systems are
being affected by regional climate changes, particularly temperature increases.  However, clearly
attributing specific regional changes in climate to emissions of greenhouse gases from human activities is
difficult, especially for precipitation.

Ocean CO2 uptake has lowered the average ocean pH (increased acidity) level by approximately 0.1
since 1750.  Consequences for marine ecosystems may  include reduced calcification by she 11-forming
organisms, and in the longer term, the dissolution of carbonate sediments.

Observations show that climate change is currently affecting U.S. physical and biological systems in
significant ways. The consistency of these observed changes in physical and biological systems and the
observed significant  warming likely cannot be explained entirely due to natural variability or other
confounding non-climate factors

Projections of Future Climate Change with Continued Increases in Elevated GHG Concentrations

Most future scenarios  that  assume  no explicit GHG mitigation actions (beyond  those  already
enacted) project  increasing  global GHG  emissions  over  the  century,  with  climbing  GHG
concentrations.  Carbon dioxide is expected to remain the dominant anthropogenic GHG over the course
of the 21st century.  The radiative forcing associated with the non-CO2 GHGs  is still significant and
increasing overtime.

Future warming over the course of the 21st century, even under scenarios of low emissions growth,
is very likely  to  be  greater than observed warming over the past century.  According  to climate
model simulations summarized by the IPCC, through about 2030, the global warming rate is affected little
by the choice of different future  emission scenarios.  By the end of the century, projected average global
warming (compared to average  temperature around 1990)  varies significantly depending on emissions
scenario and climate sensitivity assumptions, ranging from 1.8 to 4.0°C (3.2 to 7.2°F), with an uncertainty
range of 1.1 to  6.4°C (2.0 to 11.5°F).

All of the U.S. is very likely to warm during this century, and most areas of the U.S. are expected to
warm by more  than the  global  average.  The largest warming is projected to occur  in winter over
northern parts  of Alaska.   In  western, central and eastern regions  of North America, the projected
warming has less seasonal variation and  is not as large, especially near the coast, consistent with less
warming over the oceans.

It is very likely that heat waves  will become more intense, more  frequent, and longer lasting in a
future warm climate, whereas cold episodes are projected to decrease significantly.

Increases in the amount  of precipitation  are very likely  in higher latitudes, while  decreases  are
likely in most subtropical latitudes and the southwestern U.S., continuing observed patterns. The
mid-continental area is expected to experience drying during summer, indicating a greater risk of drought.
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Intensity of precipitation events is projected to increase in the U.S. and other regions of the world.
More intense precipitation is expected to increase the risk of flooding and result in greater runoff and
erosion that has the potential for adverse water quality effects.

It is likely  that hurricanes will become more intense, with stronger peak winds and more heavy
precipitation associated with ongoing increases of tropical sea surface temperatures.  Frequency changes
in hurricanes are currently too uncertain for confident projections.

By the end of the  century, sea level is projected by IPCC to rise between 0.18 and 0.59 meters
relative to  around  1990 in the absence of increased dynamic ice sheet loss. Recent rapid changes at
the edges of the Greenland and West Antarctic ice sheets show acceleration of flow and thinning.  While
understanding of these ice sheet processes is incomplete, their inclusion  in models would likely lead to
increased sea-level projections for the end of the 21st century.

Sea ice extent is projected to shrink in the Arctic under all IPCC emission scenarios.

Projected Risks and Impacts Associated with Future Climate Change

Risk to society, ecosystems, and many natural Earth processes increase with increases in both the
rate and magnitude of climate change.  Climate warming may increase the possibility of large,
abrupt regional or  global climatic events (e.g., disintegration of the Greenland Ice Sheet or collapse
of the West Antarctic Ice Sheet). The partial deglaciation of Greenland (and possibly West Antarctica)
could be triggered by a sustained temperature increase of 1 to 4°C above 1990 levels. Such warming
would  cause a 4 to 6 meter rise in  sea level, which would  occur over a time period  of centuries  to
millennia.

CCSP reports that climate change has the potential to accentuate the disparities already evident in
the American health  care systems,  as many of the expected  health effects  are likely to fall
disproportionately  on the poor, the elderly, the disabled, and the uninsured.  IPCC reports with very
high confidence that climate change impacts  on human health in U.S.  cities will be compounded by
population growth and an aging population.

Severe heat waves  are projected to intensify in magnitude and duration over the portions of the
U.S. where these events already occur, with potential increases in mortality and morbidity, especially
among the elderly, young and frail.

The IPCC projects reduced  human mortality from cold exposure through 2100.  It is not clear
whether reduced mortality from cold will be greater or less than increased heat-related mortality in the
U.S. due to climate change.

Increases in regional ozone pollution relative to ozone levels without climate change are expected
due to higher temperatures  and weaker circulation in U.S. and other world cities  relative to  air
quality levels without climate change. Climate change is expected to increase regional ozone pollution,
with associated risks in respiratory infection, aggravation of asthma, and premature death. In addition to
human health effects, tropospheric ozone has significant adverse effects on crop yields, pasture and forest
growth and species composition.  The directional effect of climate change on ambient particulate matter
levels remains uncertain.

CCSP concluded that, with increased CO2 and temperature, the life cycle of grain and oilseed crops
will likely progress more rapidly.  But, as temperature rises, these crops will increasingly begin to
experience failure, especially if climate variability increases and precipitation lessens or becomes
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more variable.  Furthermore, the marketable yield of many horticultural crops - e.g., tomatoes, onions,
fruits - is very likely to be more sensitive to climate change than grain and oilseed crops.

Higher  temperatures will very likely reduce livestock production during the summer season, but
these losses will very likely be partially offset by warmer temperatures during the winter season.

Cold-water fisheries will likely be negatively affected; warm-water fisheries will generally benefit;
and the results for cool-water fisheries will be mixed, with gains in the northern and losses in the
southern portions of ranges.

Climate change has very likely increased the size and number of forest fires, insect outbreaks, and
tree mortality in the interior west, the Southwest, and Alaska, and  will continue to do so. An
increased  frequency of disturbances  like wildfire and  insect  outbreaks is at least as important to
ecosystem function as incremental changes in temperature, precipitation, atmospheric CO2,  nitrogen
deposition, and ozone pollution. IPCC estimated that overall forest growth for North America as a whole
will likely increase modestly (10-20%) as a result of extended growing seasons and elevated CO2 over the
next century, but with important spatial and temporal variation.

Coastal  communities and habitats  will  be increasingly stressed  by  climate change  impacts
interacting with development and pollution.  Sea level is rising along much of the U.S. coast, and the
rate of change will increase in the future, exacerbating the impacts of progressive inundation, storm-surge
flooding, and shoreline erosion.  Storm impacts are likely to be more severe, especially along the Gulf and
Atlantic coasts.  Salt marshes,  other coastal habitats, and dependent species  are threatened by sea-level
rise, fixed structures blocking  landward migration, and changes in  vegetation.  Population growth and
rising value  of infrastructure in  coastal areas increases  vulnerability to climate  variability and future
climate change.

Climate change will likely further constrain already over-allocated water resources in some sections
of the U.S.,  increasing competition  among agricultural,  municipal, industrial, and ecological  uses.
Although water management practices in the U.S.  are generally  advanced, particularly in the West, the
reliance on past conditions as the basis for current and future planning will no longer be appropriate, as
climate  change  increasingly  creates conditions  well outside  of historical  observations.  Rising
temperatures will diminish snowpack and increase evaporation, affecting seasonal availability of water.
In the Great Lakes and major river systems, lower levels are likely to exacerbate challenges relating to
water  quality,  navigation, recreation,  hydropower  generation,   water  transfers,  and  bi-national
relationships.  Decreased water supply and lower water levels are likely to exacerbate challenges relating
to aquatic navigation in the U.S.

Higher  water temperatures, increased precipitation intensity, and longer periods of low flows will
exacerbate many forms of water pollution, potentially making attainment of water quality goals  more
difficult. As waters become warmer,  the aquatic life they now support will be replaced by other species
better adapted to warmer water.  In  the long term,  warmer water and changing flow may result in
deterioration of aquatic ecosystems.

Ocean acidification is projected  to continue, resulting  in the  reduced biological production of
marine calcifiers, including corals.

Climate change is likely to affect both U.S. energy use and  energy production and physical and
institutional   infrastructures;   and   will  likely  interact  with  and  possibly  exacerbate   ongoing
environmental  change and environmental  pressures in  settlements, particularly  in  Alaska where
indigenous communities are facing major environmental and cultural impacts. The U.S. energy sector,
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which  relies heavily on water for hydropower and cooling capacity, may be adversely impacted by
changes to water supply and quality in reservoirs and other water bodies. Water infrastructure, including
drinking water and wastewater treatment plants, and sewer and stormwater management systems, will be
at greater risk of flooding, sea level rise and storm surge, low flows, and other factors that could impair
performance.

Disturbances such as wildfires and insect  outbreaks are increasing in  the U.S.  and are likely to
intensify in a warmer future with drier soils and longer growing seasons.  Although recent climate
trends have increased vegetation growth, continuing increases  in disturbances are likely to limit carbon
storage, facilitate invasive species, and disrupt ecosystem services.

Over the 21st century, changes in climate will cause species to shift north and to higher elevations
and fundamentally rearrange U.S. ecosystems. Differential  capacities for range shifts and constraints
from development, habitat fragmentation, invasive species, and broken ecological connections will alter
ecosystem structure, function, and services.

Within settlements experiencing climate change, certain parts of the population may be especially
vulnerable; these include the poor, the elderly, those already  in poor health, the disabled, those living
alone, those with limited rights and power (such as recent immigrants with limited English skills), and/or
indigenous  populations dependent  on one or a few resources. Thus, the potential impacts of climate
change raise environmental justice issues.

Climate  change  impacts in certain regions  of the  world may exacerbate problems  that raise
humanitarian, trade and national security issues for the U.S. The IPCC identifies the most vulnerable
world regions as the Arctic, because of the effects of high rates of projected warming on natural systems;
Africa, especially the sub-Saharan region, because of current  low adaptive capacity as well as climate
change; small islands, due to high exposure of population and  infrastructure to risk of sea-level rise and
increased storm surge; and Asian mega-deltas, such as the Ganges-Brahmaputra and the Zhujiang, due to
large populations and high exposure to sea level rise, storm surge and river flooding. Climate change has
been described as a potential threat multiplier with regard to national security issues.
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Section 1

Introduction and Background

The purpose of this document is to provide scientific and technical information for an endangerment
analysis regarding greenhouse gas (GHG) emissions from new motor vehicles and engines under section
202(a) of the Clean Air Act. Section 202 (a)(l) of the Clean Air Act states that:

       the Administrator shall by regulation prescribe  (and  from time to time  revise)... standards
       applicable to the emission of any air pollutant from any class or classes of new motor vehicles ...,
       which in his judgment cause, or contribute to, air pollution which may reasonably be  anticipated
       to endanger public health or welfare.

Thus, absent some other statutory provision,  before EPA may issue standards addressing emissions of an
air  pollutant  from new  motor vehicles or new motor vehicle engines  under section 202(a),  the
Administrator must make a so-called "endangerment finding." That finding is a two step test. First, the
Administrator must decide if, in her judgment, air pollution may reasonably be anticipated to endanger
public health or welfare.  Second, the Administrator must decide whether, in her judgment, emissions of
any air pollutant from new motor vehicles or engines cause or contribute to this air pollution.  If the
Administrator answers both questions in the affirmative, EPA shall issue standards under section 202(a).

This document itself does not convey any judgment or conclusion regarding  the  two steps  of the
endangerment finding, as these decisions are ultimately left to the judgment of the Administrator.

l(a)   Scope and Approach of this Document

The primary GHGs that are directly emitted by human activities in general are those reported in  EPA's
annual Inventory of U.S.  Greenhouse  Gas  Emissions and Sinks and  include carbon  dioxide  (CO2),
methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs)  and sulfur
hexafluoride (SF6). The primary effect of these gases is their influence on the climate system by trapping
heat in the atmosphere that would otherwise escape to space.  This heating effect (referred to as radiative
forcing) is very likely to be the cause of most of the observed global warming over the last 50 years.
Global warming and climate change can, in turn, affect health, society and the environment.  There also
are some cases where these gases have other non-climate effects.  For example, elevated concentrations of
CO2 can lead  to ocean acidification  and stimulate terrestrial  plant growth, and  CFLt emissions can
contribute to background levels of tropospheric ozone, a criteria pollutant. These  effects may in turn be
influenced by climate change in certain cases.  Carbon dioxide and other GHGs can also have direct
health effects but at concentrations far in excess of current or projected future ambient concentrations.

This document reviews a wide range of observed and projected vulnerabilities, risks and impacts due to
the  elevated levels of GHGs in the atmosphere and associated climate change. Any known or expected
benefits of elevated atmospheric concentrations of GHGs or of climate  change  are documented as well
(i.e., impacts can mean either positive or negative consequences). The extent to which observed climate
change can be attributed to anthropogenic GHG emissions is assessed. The term "climate change" in this
document generally refers to climate change  induced by human activities, including activities that emit
GHGs. Future projections of climate change, based primarily on future scenarios of anthropogenic GHG
emissions, are shown for the global and national scale.

The focus of the vulnerability, risk and impact assessment is primarily within the U.S. However, given
the global nature of climate change, there is a brief review of potential international impacts. Greenhouse

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gases, once emitted, become well mixed in the atmosphere, meaning U.S. emissions can affect not only
the U.S. population and environment but other regions of the world as well; likewise, emissions in other
countries can affect the U.S. Furthermore, impacts in other regions of the world may have consequences
that transcend national boundaries and raise concerns for the U.S.

The  timeframe over which vulnerabilities, risks and  impacts are considered  is consistent  with the
timeframe over which GHGs,  once emitted, have an effect on climate, which is decades to centuries for
the primary GHGs of concern.  Therefore, in addition to reviewing recent observations, this document
generally considers the next several decades, the time period out to around 2100, and for certain impacts
the time period beyond 2100.

Adaptation to climate change  is a key focus area  of the  climate change research community.  This
document, however, does not focus  on adaptation because adaptation is essentially  a response to any
known and/or perceived risks due to climate change. Likewise, mitigation measures  to reduce GHGs,
which could also reduce long-term risks, are not addressed.  The purpose of this document is to review the
effects of climate change and not to assess any speculative policy or societal response to climate change.
Adaptation will  be mentioned to the extent that  the  impacts projections themselves  contain some
embedded assumptions about future adaptation.3
 1 A brief overview of adaptation is provided in Appendix A.

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  Box 1.1, Peer review, publication and approval processes for IPCC, CCSP and NRC reports

  Intergovernmental Panel on Climate Change
  The World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP)
  established the Intergovernmental Panel on Climate Change (IPCC) in 1988.  It bases its assessment mainly on
  peer reviewed and published scientific/technical literature. IPCC has established rules and  procedures for
  producing its assessment reports. Report outlines are agreed to by government representatives in consultation
  with the IPCC bureau.  Lead authors are nominated by governments and are selected by the respective IPCC
  Working Groups on the basis of their scientific credentials and with due consideration for broad geographic
  representation. For Working Group I there were 152 coordinating lead authors, and for Working Group II 48
  coordinating lead authors. Drafts prepared by the authors are subject to two rounds of review; the second round
  includes government review.  For the IPCC Working Group I  report, over 30,000 written comments were
  submitted by over 650 individual experts, governments and international organizations. For Working Group II
  there were  910 expert reviewers.   Review Editors for  each chapter are responsible for ensuring that all
  substantive government and expert review comments receive appropriate consideration. For transparency, IPCC
  documents how every  comment is addressed. Each Summary for Policymakers is approved line-by-line, and the
  underlying  chapters are then  accepted, by government delegations  in formal plenary sessions.  Further
  information about IPCC's principles and procedures can be found at: OHhttp://www.ipcc.ch/about/procd.htm.

  U.S. Climate Change Science Program
  The CCSP has identified 21 synthesis and assessment products (SAPs) that address the highest priorities for U.S.
  climate change research, observation and decision-support needs. As of January 16th, 2009, all 21 synthesis and
  assessment products had been completed. Different agencies have been designated the lead for different  SAPs;
  EPA is the designated lead for three of the six SAPs addressing impacts and adaptation. For each SAP, there is
  first a prospectus that  provides an outline, the proposed authors and process for completing the SAP; this goes
  through two stages of expert, interagency and public review. Authors produce a first draft which goes through
  expert review; a second draft is posted for public review. The designated lead agency ensures that the third draft
  complies  with the  Information Quality Act.   Finally the SAP is  submitted to  the National  Science  and
  Technology Council (NSTC), a  Cabinet-level council that coordinates science and technology research  across
  the Federal government, for approval. Further information about  the clearance and review procedures for the
  CCSP  SAPs  can  be  found  at:   lHhttp://www.climatescience.gov/Library/sap/sap-guidelines-clarification-
  aug2007.htm.

  National Research Council of the U.S. National Academy of Sciences
  The National  Research Council (NRC) is part of the National Academies,  which also comprise the National
  Academy of Sciences, National Academy of Engineering and Institute of Medicine. They are private, nonprofit
  institutions that provide science, technology and health policy advice under a congressional charter.   The NRC
  has become the principal operating agency of both the National  Academy of Sciences and the National Academy
  of Engineering  in  providing services to the  government,  the  public  and the scientific  and engineering
  communities.  Federal agencies  are the primary financial sponsors of the Academies' work.  The Academies
  provide independent advice; the external sponsors have no  control over  the conduct of a study once the
  statement of task and budget are finalized. The NRC 2001 study, Climate Change Science: An Analysis of Some
  Key Questions,  originated  from a  White House request.  The  NRC 2001 study, Global Air Quality: An
  Imperative for Long-Term Observational Strategies, was supported by EPA and NASA.  The NRC 2004  study,
  Air Quality Management in the United States, was supported by EPA. The NRC 2005 study, Radiative Forcing
  of Climate Change: Expanding the Concept and Addressing Uncertainties, was in response to a CCSP request,
  and supported by NOAA. The NRC 2006 study, Surface Temperature Reconstructions for the Last 2,000  Years,
  was requested by the Science Committee of the U.S. House of Representatives. Each NRC report is authored by
  its own committee of experts, reviewed by outside experts, and approved by the Governing Board of the NRC.
Uncertainties and  confidence  levels associated with the scientific conclusions  and  findings  in this
document are reported, to the extent that such information was provided in the original scientific reports
upon which this document is based.

l(b)    Data and Scientific Findings Considered by EPA

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This document relies most heavily on existing, and in most cases very recent, synthesis reports of climate
change  science and  potential  impacts, which have gone  through their own peer-review processes
including review by the U.S. Government.   The information in this document has been developed and
prepared in a manner that is consistent with EPA's Guidelines for Ensuring and Maximizing the Quality,
Objectivity, Utility and Integrity of Information Disseminated by the Environmental Protection Agency.
In addition to  its reliance  on existing  and primarily recent synthesis reports  from  the peer reviewed
literature, it also underwent a technical review by 12 federal climate change experts, internal EPA review,
and interagency review.

These  core  reference (Table  1.1) documents include  the 2007  Fourth Assessment Report of the
Intergovernmental Panel on Climate Change (IPCC),  Synthesis and Assessment Products of the U.S.
Climate Change  Science Program (CCSP), National Research Council  (NRC) reports under the U.S.
National Academy of Sciences  (NAS), the  EPA  annual  report  on U.S.  greenhouse gas emission
inventories and the EPA assessment of the impacts of global change on regional U.S. air quality.
Table 1.1, Core references relied upon most heavily in this document.
Science body/author
IPCC
IPCC
IPCC
CCSP
CCSP
CCSP
CCSP
CCSP
CCSP
CCSP
CCSP
CCSP
CCSP
CCSP
CCSP
CCSP
CCSP
CCSP
CCSP
NRC
NRC
NRC
NRC
EPA
EPA
AC I A
Short Title and Year of Publication
Working Group I: The Physical Science Basis (2007)
Working Group II: Impacts, Adaptation and Vulnerability (2007)
Working Group III: Mitigation of Climate Change (2007)
SAP 1.1: Temperature Trends in the Lower Atmosphere (2006)
SAP 1.2: Past Climate Variability and Change in the Arctic and at High Latitudes
(2009)
SAP 1.3: Re-analyses of Historical Climate Data (2008)
SAP 2.1: Scenarios of GHG Emissions and Atmospheric Concentrations (2007)
SAP 2.3: Aerosol Properties and their Impacts on Climate
SAP 2.4: Trends in Ozone-Depleting Substances (2008)
SAP 3.1: Climate Change Models (2008)
SAP 3.2: Climate Projections (2008)
SAP 3.3: Weather and Climate Extremes in a Changing Climate (2008)
SAP 3.4: Abrupt Climate Change (2008)
SAP 4.1: Coastal Sensitivity to Sea-Level Rise (2009)
SAP 4.2: Thresholds of Change in Ecosystems (2009)
SAP 4.3: Agriculture, Land Resources, Water Resources, and Biodiversity (2008)
SAP 4.5: Effects on Energy Production and Use (2007)
SAP 4.6: Analyses of the Effects of Global Change on Human Health (2008)
SAP 4.7: Impacts of Climate Change and Variability on Transportation Systems
(2008)
Climate Change Science: Analysis of Some Key Questions (2001)
Radiative Forcing of Climate Change (2005)
Surface Temperature Reconstructions for the Last 2,000 Years (2006)
Potential Impacts of Climate Change on U.S. Transportation (2008)
Impacts of Global Change on Regional U.S. Air Quality(2009)
Inventory of U.S. Greenhouse Gas Emissions and Sinks (2008)
Arctic Climate Impact Assessment (2004)

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EPA is relying most heavily on these synthesis reports because they 1) are very recent and represent the
current state of knowledge on climate change science, vulnerabilities and potential impacts; 2) have
assessed numerous individual  studies in order to draw general conclusions about the state of science; 3)
have been reviewed and formally accepted by, commissioned by,  or in some  cases authored by, U.S.
government agencies and individual government scientists and provide EPA with assurances that this
material has  been well vetted by  both the  climate  change research community and  by the U.S.
government; and 4) in many cases, they reflect and convey the consensus conclusions of expert authors.
Box 1.1 describes the peer review and publication approval processes of IPCC,  CCSP and NRC reports.
Peer review and  transparency are key to  each of these research organizations' report  development
process.  In compliance with the U.S. EPA's information quality guidelines,  this document relies on
information that is objective, technically sound and vetted, and of high integrity.  Box 1.2  describes the
lexicon used  by IPCC to communicate uncertainty and confidence  levels associated with the most
important IPCC findings; this document employs the same lexicon when referencing IPCC statements.
The IPCC Fourth Assessment Report (AR4) consists of three volumes: Working Group I addresses the
physical science of climate change; Working Group II addresses impacts,  vulnerabilities and adaptation;
and Working  Group  III  addresses  mitigation (i.e.,  emission reduction)  measures.    These  IPCC
assessments are generally global in scope but provide information at the country and regional level as
well.  The Working Group II volume contains individual chapters devoted to the key climate change
impact sectors, which are  also  addressed in this  document (e.g., human health,  agriculture, water
resources, etc.), as well as chapters devoted to key regions.  This document relies heavily  on the North
America chapter of the IPCC Working Group II report, though this chapter may not provide as much
regional detail within the U.S. as did the 2000 report, Climate Change Impacts on the United States: The
Potential Consequences of Climate Variability and Change (NAST, 2000).

Throughout this document, when these various assessments are referred to in general or as a whole, the
full reports are cited.   For example,  a general reference to the  CCSP  report "Weather and Climate
Extremes in a Changing Climate" is cited as "CCSP, 2008i" (tbe "i" differentiates the report from other
CCSP reports  published that same  year).   When specific  findings or conclusions from these larger
assessment reports are referenced, citations are given for the relevant individual chapter or section.  For
example, a finding from CCSP, 2008i chapter 5 "Observed Changes in Weather and Climate" by Kunkel
et al. is cited as "Kunkel et al., 2008."

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  Box 1.2: Communication of Uncertainty in the IPCC AR4 and U.S. CCSP SAPs

  IPCC AR4 Uncertainty Treatment

  A set of terms to describe uncertainties in current knowledge is common to all parts of the IPCC AR4 based on the
  Guidance Notes for Lead Authors of the IPCC Fourth Assessment Report on Addressing Uncertainties
  (http://www.ipcc.ch/activity/uncertainryguidancenote.pdf), produced by the IPCC in July 2005.  Any use of these
  terms in association with IPCC statements in this Endangerment document carries the same meaning as originally
  intended in the IPCC Fourth Assessment Report.

  Description of confidence

  On the basis of a comprehensive reading of the literature and their expert judgment, authors have assigned a
  confidence level to major statements on the basis of their assessment of current knowledge, as follows:

         Very high confidence            At least 9 out of 10 chance of being correct
         High confidence                 About 8 out of 10 chance
         Medium confidence              About 5 out of 10 chance
         Low confidence                 About 2 out of 10 chance
         Very low confidence             Less than a 1 out of 10 chance

  Description of likelihood

  Likelihood refers to a probabilistic assessment of some well defined outcome having occurred or occurring in the
  future, and may be based on quantitative analysis or an elicitation of expert views. When authors evaluate the
  likelihood of certain outcomes, the associated meanings are:

         Virtually certain                 >99% probability of occurrence
         Very likely                     90 to 99% probability
         Likely                         66 to 90% probability
         About as likely as not            33  to 66% probability
         Unlikely                        10 to 33% probability
         Very unlikely                   1 to 10% probability
         Exceptionally unlikely           < 1 % probability

  U.S. CCSP SAP Uncertainty Treatment

  In many of its SAPs, the U.S.  CCSP uses the same or similar terminology to the IPCC to describe confidence and
  likelihood. However, there is some variability from report to report, so readers should refer to the individual SAPs
  for a full accounting of the respective uncertainty language. In this document, when referencing CCSP reports, EPA
  attempted to reflect the underlying CCSP reports' terminology for communicating uncertainty.
In some cases, this document references other reports and studies in addition to the core references of
IPCC, CCSP, NRC, and, for greenhouse gas emissions, EPA. These references are  primarily for major
reports and studies  produced  by U.S.  federal and  state government agencies.  This  document also
references data made available by other government agencies, such as NOAA and NASA.

EPA just recently completed and published an assessment of the literature on the effect of climate change
on air quality (EPA, 2009). Therefore, because EPA evaluated the literature itself in the preparation of
that assessment, EPA does cite some individual studies it reviewed in its summary of this topic in Section
8. Also, for Section  15a on the national security implications of climate change, this document cites a
number of analyses and publications, from both inside and outside the government, since IPCC and CCSP
assessments have not explicitly addressed these issues.

EPA  recognizes that scientific research is very active in  many areas  addressed  in this  document (e.g.
aerosol effects on climate, climate  feedbacks such  as water vapor, and internal and external climate
forcing mechanisms)  as well as for some emerging issues (e.g. ocean  acidification,  and  climate  change

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effects on water quality). EPA recognizes the potential importance of new scientific research, but, except
as described above, studies that have not yet been assessed by the scientific community are not included
in this document.

l(c)    Roadmap for this Document

The remainder of this document is structured as follows:

•  Part II, Section 2 describes sources of U.S. and global GHG emissions.  How anthropogenic GHG
   emissions  have contributed to  changes in global  atmospheric  concentrations  of GHGs  is  also
   described.
•  Part III, Sections 3-6 describe the effects of elevated concentrations of GHGs including any direct
   health and environmental effects;  the heating or radiative forcing effects on the climate  system;
   observed climate change (e.g., changes in temperature, precipitation and sea level rise)  for the U.S.
   and  for  the globe;  recent conclusions about the extent to which observed climate change can be
   attributed to the elevated levels of GHG concentrations; and summarize future projections of climate
   change—driven primarily by scenarios of anthropogenic GHG emissions—for the remainder of this
   century.
•  Part IV, Sections  7-14 review recent findings  for the broad range of observed and projected
   vulnerabilities, risks and impacts for human health,  society and the environment within the U.S. due
   to climate change. The specific sectors and systems include:
       o  Human health (7)
       o  Air Quality (8)
       o  Food Production and Agriculture (9)
       o  Forestry (10)
       o  Water Resources (11)
       o  Coastal Areas (12)
       o  Energy, Infrastructure and Settlements (13)
       o  Ecosystems and Wildlife (14)
•  Part V, Section 15 briefly addresses some  key international impacts that may occur due to  climate
   change, with a view towards how some of these impacts may in turn affect the U.S.
       o  International Impacts (15)

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                               Part II



    Emissions and Elevated Concentrations of Greenhouse Gases

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Section 2

Greenhouse Gas Emissions and Concentrations

This section first describes current  U.S. and  global anthropogenic greenhouse gas (GHG) emissions.
Future GHG emission scenarios are  described in Part III, Section 6, however, these scenarios primarily
focus on global emissions, rather than detailing individual U.S.  sources.  This section then focuses on
historic and current global GHG atmospheric concentrations.

2(a)   U.S. and global greenhouse gas emissions

To track the national trend in GHG emissions and carbon removals since 1990, EPA develops the official
U.S. GHG inventory each year.  In accordance with Article 4.1 of the United Nations Framework
Convention on Climate Change (UNFCCC), the Inventory of U.S. Greenhouse Gas Emissions and Sinks
includes  emissions  and removals  of carbon  dioxide (CO2), methane  (CFLO,  nitrous oxide  (N2O),
hydrofluorocarbons  (HFCs), perfluorocarbons  (PFCs),  and sulfur hexafluoride (SF6) resulting from
anthropogenic activities in the U.S.

Total emissions are presented in  teragrams4 (Tg)  of  CO2  equivalent (TgCO2eq), consistent with
Intergovernmental  Panel  on Climate Change  (IPCC) inventory guidelines.   To  determine  the CO2
equivalency of different GHGs, in order to sum and compare different GHGs,  emissions of each gas are
multiplied by its global warming potential (GWP), a factor which relates it to CO2 in its ability  to trap
heat in the atmosphere over a certain timeframe. Box 2.1 provides more information about GWPs and the
GWP values used in this section of the report.
  Box 2.1: Global Warming Potentials used in this document

  In accordance with UNFCCC reporting procedures, the U.S. quantifies GHG emissions using the 100-year time
  frame values for GWPs established in the IPCC Second Assessment Report (SAR) (IPCC, 1996).  The GWP
  index is defined as the cumulative radiative forcing between the present and some chosen later time horizon (100
  years) caused by a unit mass of gas emitted now.  All GWPs are expressed relative to a reference gas, CO2,
  which is assigned a GWP = 1. Estimation of the GWPs requires knowledge of the fate of the emitted gas and the
  radiative forcing due to the amount remaining in the atmosphere. To estimate the CO2 equivalency of a non-CO2
  GHG, the appropriate GWP of that gas is multiplied by the amount of the gas emitted.

                100-year GWPs
                C02                  1
                CH4                  21
                N2O                  310
                HFCs                 140 to 6,300 (depending on type of HFC)
                PFCs                  6,500 to 9,200 (depending on type of PFC)
                SF6                   23,900

  The GWP for CH4 includes  the direct effects and those indirect effects due  to the production of tropospheric
  ozone and stratospheric water vapor.  These  GWP values have been updated twice, in the  IPCC third (TAR
  2001) and fourth assessment reports (AR4 2007).
 1 teragram (Tg) = 1 million metric tons.  1 metric ton = 1,000 kg = 1.102 short tons = 2,205 Ibs.

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The national inventory totals used in this report for the U.S. (and other countries) are gross emissions,
which include GHG emissions from the electricity, industrial, commercial, residential and agriculture
sectors. Emissions and sequestration occurring in the land-use, land-use change and forestry sector (e.g.,
forests, soil carbon etc.) are  not included in gross  national totals, but are  reported under net emission
totals (sources and sinks), according to international practice. In the U.S., this sector is a significant net
sink, while in some developing countries it is a significant net source of emissions.

Also excluded from emission totals in this report are bunker fuels (fuels used for international transport).
According to UNFCCC reporting guidelines, emissions from the consumption of these fuels should be
reported separately,  and  not included in national emission totals,  as  there exists no agreed upon
international formula for allocation between countries.

The most recent inventory was published in 2008 and includes annual data for the years 1990-2006.

U.S. Greenhouse Gas Emissions

In 2006, U.S. GHG emissions were 7,054.2 TgCO2eq (see Figure 2.1).5 The dominant gas emitted is CO2,
mostly from fossil fuel combustion  (84.8%) (EPA, 2008).  Weighted by GWP, CH4 is the second largest
component of emissions, followed by N2O, and the high-GWP fluorinated gases (HFCs, PFCs, and SF6).
Electricity generation (2377.8 TgCO2eq) is the largest emitting sector, followed by transportation (1969.5
TgCO2eq) and industry (1371.5 TgCO2eq) (EPA, 2008) (Figure 2.2). Agriculture and the commercial and
residential sectors emit 533.6 TgCO2eq, 394.6 TgCO2eq, and 344.8 TgCO2eq, respectively (EPA, 2008).
Removals of carbon through  land use, land-use change and forestry activities are not included in Figure
2.2, but are significant; net sequestration is estimated to be 883.7 TgCO2eq in 2006, offsetting  12.5% of
total emissions (EPA, 2008).
5 Per UNFCCC reporting requirements, the U.S. reports its annual emissions in gigagrams (Gg) with two significant
digits (http://unfccc.int/files/national_reports/annex_i_ghg_inventories/national_inventories_sub-
missions/application/x-zip-compressed/usa_2007_crf_l lapr.zip). For ease of communication of the findings, the
Inventory of U.S. Greenhouse Gas Emissions and Sinks report presents total emissions in Tg with one significant
digit.
                                                10

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Figure 2.1: Total U.S. Greenhouse Gas Emissions: 1990-2006
      8,000

      7,000

      6,000

   Eq.5,000
      3,000

      2,000

      1,000

         0
6,148  6,106 6,192
             6343  6,435 6,494 u'

            1990 1991 1992 1993 1994 1995 1996 1997 1998  1999 2000 2001 2002 2003 2004 2005 2006
Source: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2006 (EPA, 2008). Excludes land-
use change and forestry and international bunker fuels.
U.S.  emissions increased
by  905.9  TgCO2eq,  or
14.7% between  1990 and
2006   (see  Figure   2.1)
(EPA,            2008).
Historically,  changes  in
fossil  fuel  consumption
have  been the  dominant
factor   affecting    U.S.
emission   trends.    The
fundamental       factors
driving this trend include
a   generally   growing
domestic  economy  over
the last 16 years, leading
to  overall  growth  in
emissions from electricity
generation  (increase  of
30.7%) and transportation
activities   (increase   of
27.9%) (EPA,  2008).  Over the same  time period, industrial,  residential,  and commercial emissions
decreased by 6.0%, 0.6%, and 0.6% respectively, while emissions increased in the agriculture  (5.3%)
sector (Figure 2.2) (EPA, 2008).
Figure 2.2: U.S. GHG Emissions Allocated to Economic Sector.
2,500 ,
2,000 -
iff 1<50°-
8
P 1,000-
500-
0-
19
Electricity Generation
	 • 	 ' Transportation
._-: — :nr 	 "^

Agriculture
Residential
90 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
Source: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2006 (EPA,
2008). All GHGs. Excludes land use, land-use change and forestry and
international bunker fuels.

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                               Figure 2.3: Total GHG Emissions for the Year 2005 by Country and for
                               U.S. Section 202a Source Categories
U.S.    Greenhouse     Gas
Emissions    from    Source
Categories   under   Section
202(a) of the Clean Air Act

Source    categories   under
Section 202(a)  of  the  Act
include passenger vehicles,
light- and heavy-duty trucks,
buses, motorcycles, and  the
cooling systems designed for
passenger comfort, as well as
auxiliary     systems     for
refrigeration.

In   2006,   section   202(a)
source categories collectively
were  the   second  largest
GHG-emitting  sector  within
the    U.S.    (behind    the
electricity generating sector),
emitting 1,665  TgCO2eq and
representing  24  percent  of
total  U.S. GHG  emissions.
Between 1990 and 2006, total
GHG emissions from passenger cars  decreased 0.9 percent, while  emissions  from light-duty trucks
increased 57 percent, largely due to the increased use of sport-utility vehicles and other light-duty trucks.

Globally in 2005, section 202(a) source category GHG emissions  represented 31 percent of global
transport GHG emissions  and 4.3 percent of total global GHG emissions (Figure 2.3).  The global
transport sector was 14 percent of all global GHG emissions in 2005.   If U.S. section 202(a) source
category GHG emissions were ranked against total GHG emissions for entire  countries, U.S. section
202(a) emissions would rank behind only China, the U.S.  as a whole, Russia and India, and  would rank
ahead of Japan, Brazil, Germany and every other country in the world.

Further detail on these emissions can be found in Appendix B of this document.

Global Greenhouse Gas Emissions

Total global emissions are calculated by summing emissions of the six greenhouse gases, by country. The
World Resources Institute compiles  data from recognized national and international data sources in its
Climate Analysis Indicators Tool (CAIT).6   Globally, total GHG emissions were 38,725.9  TgCO2eq in
2005, the  most recent year for which data are available for all countries and all GHGs  (WRI, 2009).7
This global total  for the year 2005  represents an increase of about  26%  from the 1990 global GHG
emission total of 30,704.9  TgCO2eq (WRI, 2009).  Excluding land use, land-use change, and forestry,
U.S. emissions were 19% of the total year 2005 global emissions, (see Figure 2.3)  (WRI, 2009).
                               Source: WRI Climate Analysis and Indicators Tool. Available at http://cait.wri.orq/.
                               Excludes land use, land-use change and forestry, and international bunker fuels.
                               More recent emissions data are available for the U.S. and other individual
                               countries, but 2000 is the most recent year for which data for all countries and all
                               gases are available.  Data accessed February 20, 2009.
6 Primary data sources referenced in CAIT include the U.S. Department of Energy's Carbon Dioxide Information
Analysis Center, the U.S. Environmental Protection Agency, the International Energy Agency and the National
Institute for Public Health and the Environment, an internationally recognized source of non-CO2 data.
7 Source: WRI Climate Analysis and Indicators Tool. Available at http://cait.wri.org/.
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2(b)   Historic and current global greenhouse gas concentrations

Greenhouse gas concentrations in the atmosphere vary over very long time scales in response to natural
influences such as geologic activity and temperature change associated with ice age cycles, but ice core
data show nearly constant concentrations of CO2, CH4 and N2O over more than 10,000 years prior to the
industrial  revolution.  However, since  the industrial revolution,  anthropogenic  GHG emissions have
resulted in substantial increases in the concentrations of GHGs in the atmosphere (IPCC, 2007d; NRC,
2001).

Carbon dioxide (CO2)

Carbon dioxide concentrations  have increased substantially from pre-industrial levels (Figure 2.4).  The
long-term trends in the CO2 concentrations are as follows (NOAA, 2009c; Forster et al., 2007):

    •   The CO2 concentration has increased about 38% from a pre-industrial value of about 280 parts per
       million (ppm) to 386 ppm (which is about 0.039% of the atmosphere by volume) in 2008s.
    •   The present atmospheric concentration of CO2  exceeds by far the natural range  over the last
       650,000 years (180 to 300 ppm) as determined from ice cores (Jansen et al., 2007).
    •   The annual CO2 concentration growth rate9 has been larger since 2000 (2000-2008 average: 2.0
       ppm  per year), than  it  has been  since  the  beginning of  continuous  direct atmospheric
       measurements (1960-2005 average: 1.4 ppm per year) although there is year-to-year variability.

Almost all of the increase in the  CO2 concentration during the Industrial Era is due to anthropogenic
emissions (Forster et al., 2007). Since the 1980s, about half of the anthropogenic emissions have been
taken  up by the terrestrial  biosphere and the  oceans, but observations demonstrate that these processes
cannot remove all of the extra flux due to human activities.   About half of the anthropogenic emissions
have remained in the atmosphere (Forster et al., 2007).
8 The 2008 value is preliminary.
9 The estimated uncertainty in the Mauna Loa annual mean growth rate is 0.11 ppm/yr.
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Methane (CH4)

Methane   concentrations  have   also   risen
substantially (Figure 2.4).  The following trends
in atmospheric methane  have been observed
according  to  NOAA's  report "State of  the
Climate  in  2007" and IPCC (Horvitz, 2008;
Forsteretal., 2007):

•   The  global atmospheric  concentration  of
    methane has increased from a pre-industrial
    value of about 715 parts per billion (ppb) to
    1732 ppb in the early 1990s, and was 1782
    ppb in 2007 - a  149% increase from pre-
    industrial levels.
•   The atmospheric concentration of methane
    in 2007 exceeds by far the natural range of
    the last 650,000 years (320 to 790 ppb) as
    determined from  ice  cores (Jansen  et  al.,
    2007).
•   Growth rates declined between the  early
    1990s and mid-2000s.  The reasons for the
    decrease in the atmospheric CH4 growth
    rate and the implications for future changes
    in its  atmospheric burden are  not  well-
    understood but are clearly related to  the
    changes  in the imbalance  between CFi4
    sources and sinks.
•   The  methane  concentration grew 7  ppb
    between 2006 and 2007, the first year-to-
    year increase since 1998. The reasons for
    the increase in 2007 are not yet known, but
    analysis of carbon monoxide measurements
    suggests it is not from biomass burning.

The   observed    increase    in    methane
concentration   is   very   likely   due    to
anthropogenic    activities,    predominantly
agriculture  and  fossil fuel use, but relative
contributions from  different  source types  are
not well determined (Forster et al., 2007).

Nitrous Oxide (N2O)

The N2O concentration has increased 23% from
its  pre-industrial  value  of 262  ppb  (Figure
2.4)to 321 ppb in 2007 ( Horvitz, 2008).  The
concentration  has  increased linearly by about
0.8 ppb yr"1 over the past few decades  and is
due primarily to human  activities, particularly
Figure 2.4: Atmospheric concentrations of carbon
dioxide, methane and nitrous oxide over the last
10,000 years
       10000
    5000
Time (before 2005)
Source: IPCC (2007d).  Atmospheric concentrations of
carbon dioxide, methane and nitrous oxide over the last
10,000 years (large panels) and since 1750 (inset panels).
Measurements are shown from ice cores (symbols with
different colors for different studies) and atmospheric
samples (red lines). The corresponding radiative forcings
(discussed in Section 2(e)) are shown on the right hand
axes of the large panels.
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agriculture and associated land use change (Forster et al., 2007).  Ice core  data show that the present
atmospheric concentration of N2O is higher than ever measured in the ice core record of the past 650,000
years (Jansen et al., 2007).

Fluorinated Gases

Industrial fluorinated gases that serve as  substitutes for CFCs  (chlorofluorocarbons)  and HCFCs
(hydrochlorofluorocarbons), such as hydrofluorocarbons (HFCs),  perfluorocarbons  (PFCs), and sulphur
hexafluoride (SF6),  have relatively low atmospheric concentrations.   Concentrations of many of these
gases have increased by large factors (between 1.3 and 4.3) between 1998 and 2005.  Their total radiative
forcing in 2005 was +0.017 [±0.002] Wm"2 and is rapidly increasing  by roughly 10% per year.  These
gases are almost entirely anthropogenic in origin (Forster et al., 2007).

Ozone  depleting substances covered by the Montreal Protocol

Chlorofluorocarbons (CFCs)  and  hydrochlorofluorocarbons  (HCFCs) are GHGs  that  are entirely
anthropogenic in  origin. Emissions of these gases  have decreased due to their phase-out under the
Montreal Protocol, and the atmospheric concentrations of CFC-11 and CFC-113 are now decreasing due
to natural removal processes (Forster et al., 2007).  Ice  core and in situ data confirm that industrial
sources are the cause of observed atmospheric increases in CFCs and HCFCs (Forster et al., 2007).

Ozone  (O3)

Tropospheric ozone is a short-lived greenhouse gas produced largely by chemical reactions of precursor
species in the atmosphere and with large spatial and temporal variability. Changes in tropospheric ozone
also occur due to  changes in transport of ozone across the tropopause  (Forster et al., 2007). Relative to
the other greenhouse gases, there is less confidence in reproducing the changes in ozone associated with
large changes in  emissions or climate, and in the simulation of observed  long-term trends in ozone
concentrations over the 20th century (Forster et al., 2007).

Aerosols (Sulfates, nitrates,organic and black carbon aerosols)

Aerosols are small, short-lived particles present in the atmosphere with widely varying size, concentration
and chemical composition, either directly emitted or formed in secondary reactions from emitted
compounds. Aerosols are removed from the atmosphere primarily through cloud processing and wet
deposition in precipitation, a mechanism that establishes average tropospheric  aerosol atmospheric
lifetimes at a week or less (CCSP, 2009a). On a global basis, aerosol mass derives predominantly from
natural sources, mainly sea salt and dust. However, anthropogenic (manmade)  aerosols, arising primarily
from a variety of combustion sources, can dominate in and downwind of highly populated and
industrialized regions, and in areas of intense agricultural burning (CCSP, 2009a). Aerosol optical
density trends observed in the satellite and surface-based data records suggest that since the mid-1990s,
the amount of anthropogenic aerosol has decreased over North America and Europe, but has increased
over parts of east and south Asia; on average, the atmospheric concentration of low latitude smoke
particles has increased, consistent with changes in emissions (CCSP, 2009a).  Ice core data from
Greenland and Northern Hemisphere mid-latitudes show a very likely rapid post-industrial era increase in
sulfate concentrations above the preindustrial background, though in recent years, sulfur dioxide
emissions have decreased globally and in many regions of the northern hemisphere.  In general, the
concentration, composition and distribution of aerosols in the paleoclimate record are not as well known
as the long-lived greenhouse gases (Jansen et al., 2007).
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                               Part III

    Global and U.S. Observed and Projected Effects from Elevated
                    Greenhouse Gas Concentrations
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Section 3

Direct Effects of  Elevated Greenhouse Gas Concentrations

Carbon dioxide and other GHGs can have direct effects that are independent of their radiative forcing on
climate (the primary effect discussed throughout this document).  Such effects are described below.

Effects on Human Health

Current and projected ambient greenhouse gas concentrations remain well below published thresholds for
any direct adverse health effects,  such  as respiratory or toxic  effects. The  literature supporting this
conclusion is described in Appendix C.

Carbon Dioxide Fertilization

Carbon dioxide  can  have stimulatory or fertilization effect on plant growth.  There  is debate and
uncertainty about the sensitivity of crop yields to the  direct effects of elevated CO2 levels. However, the
IPCC (Easterling et al., 2007) concluded that elevated CO2 levels are expected to result in small beneficial
impacts on crop yields. The IPCC confirmed the general conclusions from its previous Third Assessment
Report in 2001.  Experimental research on crop responses to elevated CO2 through the FACE (Free Air
CO2 Enrichment)10 experiments indicate that, at ambient CO2 concentrations of 550 ppm (approximately
double the concentration from pre-industrial times) crop yields increase under unstressed conditions by
10-25% for C3 crops, and by 0-10% for C4 crops (medium confidence)11. Crop model simulations under
elevated CO2 are consistent with these ranges (high confidence) (Easterling et al., 2007). Globally and in
the U.S., high temperatures and ozone exposure, however, can significantly limit the direct stimulatory
CO2 response (see also Section 8 on Air Quality and Section 9 on Food Production and Agriculture).

Elevated CO2 has raised an issue about forage quality for livestock. Elevated CO2 can increase the carbon
to nitrogen ratio in forages and thus reduce the nutritional value of those grasses and thus affect animal
weight and performance.  The decline  under elevated CO2 of C4  grasses,  however, which  are less
nutritious than C3 grasses, may compensate for the reduced protein. Yet the opposite is expected under
associated temperature increases (Hatfield et al., 2008).

At much higher ambient CO2 concentrations, such as those areas exposed to natural CO2 outgassing due
to volcanic activity, the main characteristic of long-term elevated CO2 zones at the surface is the lack of
vegetation (IPCC, 2005). New CO2 releases into vegetated areas cause noticeable  die-off In those areas
where significant impacts to vegetation  have  occurred, CO2 makes up about 20-95% of the soil gas,
whereas normal soil  gas usually contains about 0.2-4% CO2. Carbon dioxide concentrations above 5%
may be dangerous for vegetation and as concentrations approach 20%, CO2 becomes  phytotoxic. Carbon
dioxide can cause death of plants through 'root anoxia', together with low oxygen concentration (IPCC,
2005).

As atmospheric CO2 increases, more CO2 is absorbed at the surface of oceans, estuaries, stream and lakes.
Increases in the  amount of dissolved CO2  and, for some  species, bicarbonate ions  (HCO3~) present in
aquatic environments will lead to higher rates of photosynthesis in submerged aquatic vegetation, similar
to the fertilization effects of CO2 enrichment on most terrestrial plants, if other limiting factors do not
10 http://www.bnl.gov/face/
11 C3 and C4 refer to different carbon fixation pathways in plants during photosynthesis.  C3 is the most common
pathway, and C3 crops (e.g., wheat, soybeans and rice) are more responsive than C4 crops such as maize.
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offset the potential for enhanced productivity. A study  cited in Nicholls et al. (2007) indicates algal
growth  may  also  respond positively to elevated  dissolved inorganic carbon (DIC), though marine
macroalgae do not appear to be limited by DIC levels. An increase in epiphytic or suspended algae would
decrease light available to submerged aquatic vegetation  and also increase the incidence of algal blooms
that lower dissolved oxygen available to fish and shellfish (Nicholls et al., 2007).

Ocean Acidification

According to the  IPCC  (Fischlin et al.,  2007)  elevated  CO2  concentrations  are  resulting in ocean
acidification which may affect marine ecosystems (medium  confidence). This is discussed further in
sections 4h, 6b, and 14a.
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Section 4

Radiative Forcing and Observed Climate Change

This section focuses primarily on the more significant effects associated with GHGs, which is their heat-
trapping ability (referred to as radiative forcing) that results in climate change.  Observed climate change
is reviewed, including changes in temperature, precipitation, and sea level rise, for the globe and the U.S.
Observed changes in  climate-sensitive physical and biological systems are also addressed,  as well as
observed trends in extreme events.  Sections 7 to  15 provide more specific information on the sectoral
implications of both the observed changes described here and the projected changes described in Section
6.

4(a)   Radiative forcing due to greenhouse gases and other factors

This section describes radiative  forcing  and the  factors  that contribute to it.  Radiative forcing is a
measure  of the change that a factor causes in altering the balance  of incoming (solar)  and outgoing
(infrared and reflected shortwave) energy in the Earth-atmosphere system, and thus shows the relative
importance of different factors in terms of their contribution to climate change.  Positive forcing means
the factor causes a warming effect and negative forcing means the factor causes a cooling effect.

Radiative forcing values  presented here for  GHGs and other factors come from  the  IPCC Fourth
Assessment Report of Working Group  I (2007).  These radiative forcing values  are the result of global
changes in atmospheric concentrations of GHGs (see  Section 2(c) above) and  other factors, and are
therefore not the result of U.S. transportation  emissions in isolation.  All  values are  for the year 2005
relative to pre-industrial times  in 1750, represent global averages, and are expressed in watts  per square
meter12 (W/m2).

IPCC (2007d) concluded that the understanding of anthropogenic warming and cooling influences on
climate has improved since the TAR,  leading to  very high confidence13 that the global average net
effect of human activities since 1750 has been one of warming, with a radiative forcing of+1.6 (+0.6 to
+2.4) W/m2.

Greenhouse gases have a positive forcing because they absorb and reradiate in  all directions outgoing,
infrared radiation that would otherwise directly escape into space.  The combined radiative forcing due to
the cumulative (i.e., 1750 to 2005) increase in atmospheric concentrations of CO2, CH4, and N2O is +2.30
W/m2  (with an uncertainty range of+2.07 to +2.53 W/m2) (see  Figure 4.1).  This positive radiative
forcing, like the observed accumulation of these gases in the atmosphere, is primarily anthropogenic in
origin. Furthermore, the IPCC (2007d) stated that the rate of increase in positive  radiative forcing due to
these three GHGs during the industrial era is "very likely to have been unprecedented in more than 10,000
years."

The positive radiative forcing due  to  CO2 is  the  largest (+1.66  ± 0.17 W/m2) (Figure 4.1), and has
increased by 20% from  1995 to 2005,  the largest change for any  decade in at least the last  200 years.
Methane is the second largest source of positive radiative forcing (+0.48 ± 0.05 W/m2).  Nitrous oxide has
a positive radiative forcing of+0.16 (±0.02) W/m2.
12 Watts per square meter is the SI unit for radiative and other energy fluxes.
13 According to IPCC terminology, "very high confidence" conveys a 9 out of 10 chance of being correct.  See Box
1.3 on page 5 for a full description of IPCC's uncertainty terms.
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The other three  GHGs reported by the  U.S. Inventory—HFCs, PFCs and SF6-
forcing in 2005 of+0.017 (±0.002) W/m2 (Forster et al, 2007).
                  -have  a total radiative
Figure 4.1: Global average radiative forcing (RF) estimates and ranges in 2005 for
anthropogenic GHG emissions and other factors
       RF Terms
          Long-lived
   greenhouse gases
              Ozone

    Stratospheric water
     vapour from CH4

       Surface albedo
           {Direct effect


          Cloud albedo
               effect


       Linear contrails
       Solar irradiance
            Total net
        anthropogenic
 RF values (W m'g)
 1.66 [1.49 to 1.83]

 0.48 [0.43 to 0.53]
 0.16 [0.14 to 0.18]
 0.34 [0.31 to

-0.05 [-0.15 to 0.05]
 0.35 [0.25 to 0.65]

 0.07 [0.02 to 0.12]


 -0.2 [-0.4 to 0.0]
  0.1 [0.0 to 0.2]


 -0.5 [-0.9 to -0.1]


 -0.7 [-1.8 to -0.3]


0.01 [0.003 to 0.03]
                                                               0.12 [0.06 to 0.30]
  1.6 [0.6 to 2.4]
                                                                              Spatial scale
                                                                                 Global
  Global


Continental
 to global


  Global


 Local to
continental

Continental
 to global

Continental
 to global


Continental
                                                                                 Global
                                                                                        LOSU
                                                                                         High
                                                                                         High
                                                                                         Med
Low
Med
- Low
Med
- Low
Low
                                                                                         Low
                                                                                         Low
                  -2        -1       _ 0         1         2
                          Radiative Forcing  (W m~2)

Source: IPCC (2007d). Global average radiative forcing (RF) estimates and ranges in 2005 for
anthropogenic carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and other important factors,
together with the typical geographical extent (spatial scale) of the forcing and the assessed level of scientific
understanding (LOSU). The net anthropogenic radiative forcing and its range are also shown. These require
summing asymmetric uncertainty estimates from the component terms, and cannot be obtained by simple
addition. Additional forcing factors not included here are considered to have a very low LOSU. Volcanic
aerosols contribute an additional natural forcing but are not included in this figure due to their episodic
nature. The range for linear contrails does not include other possible effects of aviation on cloudiness.	
The ozone-depleting substances  covered  under  the  Montreal Protocol  (chlorofluorocarbons (CFCs),
hydrochlorofluorocarbons  (HCFCs),  and  chlorocarbons) are  also  strong  GHGs  and,  as a  group,
contributed +0.32 (±0.03) W/m2 to anthropogenic radiative forcing  in 2005.  Their  radiative forcing
peaked in 2003 and is now beginning to decline (Forster et al., 2007).   The radiative forcing due to the
destruction of stratospheric ozone by these gases  is estimated to be -0.05 ± 0.10 W/m2 with a medium
level of scientific understanding (Solomon et al., 2007).

In addition to the six main GHGs  directly emitted by human activities,  and the gases covered  by the
Montreal Protocol, there are additional anthropogenic and natural factors that contribute to both positive
and negative forcing.
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With regard to climate change,  ozone  affects  the radiative budget of the atmosphere through  its
interaction with both  shortwave and  longwave  radiation (Forster  et al.  2007).   Tropospheric ozone
changes due to emissions of ozone-forming chemicals, or precursors (nitrogen oxides, carbon monoxide,
and hydrocarbons including methane),  contribute  a positive forcing of+0.35 (+0.25 to +0.65) W/m2. As
described in CCSP  (2008d),  robust model simulations project  climate change  will also increase the
radiative forcing from  ozone by increasing stratosphere-troposphere  exchange and hence ozone near the
tropopause where  it is most important radiatively.   Unlike the  GHGs  mentioned above, tropospheric
ozone is not as well-mixed in the global atmosphere because its  atmospheric lifetime is on the order of
weeks to months (versus decades to centuries for the well-mixed GHGs).  Tropospheric ozone is a criteria
air pollutant under the U.S. Clean Air Act.

Emissions of ozone precursors and other substances also contribute  to changes in levels of the reactive
gas OH (the hydroxyl  free radical).  OH is a key chemical species that influences the lifetimes and thus
radiative forcing values of CH4, HFCs, HCFCs and ozone; it also plays an important role in the formation
of sulfate, nitrate and some organic aerosol species. (Forster et al. 2007).

Anthropogenic emissions of aerosols contribute to both positive and negative radiative forcing.  Aerosols
are non-gaseous substances other than water or ice that are  suspended in the atmosphere, and are either
solid particles or liquid droplets.  Most aerosols, such as sulfates (which are  mainly the result of SO2
emissions from fossil fuel burning), exert a negative forcing or cooling effect, as they reflect and scatter
incoming solar radiation.  Some aerosols, such as black carbon, cause a positive forcing by absorbing
incoming solar radiation.  IPCC (2007d) estimated that the net effect of all anthropogenic increases in
aerosols (primarily sulfate, organic carbon, black carbon, nitrate and dust) produce a cooling effect, with a
total direct radiative forcing of-0.5 (-0.9 to -0.1) W/m2 and an additional indirect cloud albedo  (i.e.,
enhanced reflectivity)14 forcing of-0.7 (-1.8 to -0.3) W/m2.  These forcings are now better understood
than at the time of the IPCC Third Assessment Report  (2001), but nevertheless remain the dominant
uncertainty in radiative forcing (IPCC, 2007d).  The direct radiative forcing  of the individual aerosol
species is less certain than the total direct aerosol  radiative forcing. The estimates are: sulphate, -0.4 (+/-
0.2)  Wm"2; fossil fuel organic carbon, -0.05 (+/-0.05)Wm"2; fossil fuel black carbon, +0.2(+/-0.15) Wm"2;
biomass burning, +0.03(+/-0.12) Wm"2; nitrate, -0.1(+/-0.1) Wm"2; and mineral dust, -0.1(+/-0.2) Wm"2.
Including both fossil fuel and biomass burning sources, the total black carbon aerosol forcing is estimated
to be 0.34 (0.09 to .59) W/m2.  In addition, black carbon can cause another positive radiative forcing
effect (+0.1 (0.0 to +0.2) W/m2) by decreasing the surface  albedo of snow and ice with a low level of
scientific understanding  (Forster et al., 2007).  A more recent estimate suggests a direct black carbon
effect of 0.9 (0.4 to 1.2) W/m2, or more than half that of CO2 (Ramanathan and Carmichael., 2008).  The
spatial distribution of aerosol forcing is very different from that of the well-mixed GHGs, and they do not
exert simple compensating  or additive effects on climate (CCSP, 2008d).  The total forcing associated
with anthropogenic aerosols is less certain than that for GHGs,  due to the indirect effects of aerosols,
including cloud formation and albedo change.

The  radiative  forcing  from increases  in stratospheric water vapor  due to oxidation of anthropogenic
increases in CH4 is estimated to be +0.07 ± 0.05 W/m2 (Solomon et al., 2007).  The level of scientific
14 In addition to directly reflecting solar radiation, aerosols cause an additional, indirect negative forcing effect by
enhancing cloud albedo (a measure of reflectivity or brightness). This occurs because aerosols act as particles
around which cloud droplets can form; an increase in the number of aerosol particles leads to a greater number of
smaller cloud droplets, which leads to enhanced cloud albedo. Aerosols also influence cloud lifetime and
precipitation but no central estimates of these indirect forcing effects are estimated by IPCC. These aerosol indirect
effects remain some of the biggest uncertainties of the climate forcing/feedback processes (CCSP 2009a).
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understanding is low because the contribution of CH4 to the corresponding vertical structure of the water
vapor change near the tropopause is uncertain.

Changes in surface albedo due to human-induced land cover changes exert a forcing of-0.2 (-0.4 to 0.0)
W/m2. Changes in solar irradiance since 1750 are estimated to cause a radiative forcing of+0.12 (+0.06
to +0.30) W/m2. This is less than half of the estimate given in IPCC's Third Assessment Report (2001),
with a low level of scientific understanding (Solomon et al., 2007).   Uncertainties remain large because
of the lack of direct observations and incomplete understanding of solar variability mechanisms over long
time scales.  Empirical associations have been reported between solar-modulated cosmic ray ionization of
the  atmosphere and global average low-level clouds cover but evidence for a systematic indirect solar
effect remains ambiguous. The lack of a proven physical mechanism and the plausibility of other causal
factors make the association between galactic cosmic ray-induced changes in aerosol and cloud formation
controversial (Solomon et al., 2007).

Although water vapor is the most abundant naturally occurring greenhouse gas, direct emissions of water
vapor due to human activities make a negligible contribution to radiative forcing (hence its  absence in
Figure 3.1).  However,  as temperatures  increase,  tropospheric water vapor concentrations  increase
representing a key positive feedback (enhances warming) but not a forcing of climate change (Solomon et
al.,  2007).  Feedbacks are defined as processes in the climate system (such as a change in water vapor
concentrations) that can  either  amplify or dampen the system's  initial response to radiative forcing
changes (NRC, 2003).

4(b)    Global Changes in Temperature

Multiple lines of evidence lead to the robust conclusion that the  climate system is warming.  The IPCC
(2007d) stated in its Fourth Assessment Report:

"Warming of the climate system is unequivocal, as is now  evident from observations  of increases in
global average air and ocean temperatures, widespread melting of snow and ice, and rising global average
sea level."

Air temperature  is a main property of climate and the most easily measured, directly  observable, and
geographically consistent indicator of climate change.  The extent to which observed changes in global
and continental temperature, and other climate factors,  can be attributed to anthropogenic emissions of
GHGs is addressed in Section 5.

Global Surface Temperatures

Surface  temperature is calculated by processing data from thousands of world-wide observation sites on
land and sea. Parts of the globe have no data, although data coverage has improved with time. The  long-
term mean temperatures are calculated by  interpolating within areas with no measurements using  the
collected data available. Biases may exist in surface temperatures due to changes in station exposure and
instrumentation over land, or changes in measurement techniques by ships and buoys in the ocean. It is
likely that these biases are largely random and therefore cancel out over large regions such as the globe or
tropics (Wigley et al., 2006).  Likewise, urban heat island effects are real but local, and have not biased
the  large-scale trends (Trenberth et al., 2007).

The following trends in global surface temperatures have been observed, according to the IPCC
(Trenberth etal, 2007):
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    Global mean surface temperatures have risen by 0.74°C ±0.18°C when estimated by a linear trend
    over the last 100 years (1906-2005) as shown by the magenta line in Figure 4.2. The warmest years
    in the instrumental record of global surface temperatures are 1998 and 2005, with 1998 ranking first
    in one estimate, but with 2005 slightly higher in the other two estimates. 2002 to 2004 are the 3rd, 4th
    and 5th  warmest years in the  series  since 1850. Eleven of the last 12 years (1995 to 2006) - the
    exception being 1996 - rank among  the 12 warmest years on record  since 1850.  Temperatures in
    2006 were similar to the average of the past 5 years.
    The warming has not been steady, as shown in Figure 4.2. Two periods of warming stand out: an
    increase of 0.35°C occurred from the 1910s to the 1940s and then a warming of about 0.55°C from
    the  1970s up to the end of 2006.  The remainder of the past 150 years has included short periods of
    both cooling and warming. The rate of warming over the last 50 years is almost double that over the
    last 100 years (0.13°C ± 0.03°C vs. 0.07°C  ± 0.02°C per decade).
Figure 4.2

      0.6

  o   0.4
  O5
  O5
  _L   0.2

      0.0
      CD
      O)
      O  -0.2
      o

       §-0.4
       O
      J5  -0.6
          -0.8
               Annual global mean temperatures (black dots) with linear fits to the data.

                                                                                  14.6
                14.4
                      3 m
                14.2   s a
                      g |
                      CD r-J-
                                                                                  14.0
                                                                                          CD
                                                                                   CD 03
                                                                                   53 a
                                                                             13.8   £• §
                                                                                   l«
                                                                             13.6  -3&
                                                                                   o QL
                                                                             13.4
                                                                             13.2
                   1860    1880    1900    1920    1940    1960    1980    2000
                                                            Period    Rate
                 •  Annual mean
                ^ Smoothed series
                I   l 5-95% decadal error bars
                                                        Year?
                                                        25
                                                        50
                                                        100
                                                        150
 °C per decade
0.177±0.052
0.128±0.026
0.074±0.018
0,045±0.012
     Source: Solomon et al., (2007). The left hand axis shows temperature anomalies relative to the 1961 to 1990
     average and the right hand axis shows estimated actual temperatures, both in °C. Linear trends are shown for
     the last 25 (yellow), 50 (orange), 100 (magenta) and 150 years (red). The smooth blue curve shows decadal
     variations with the decadal 90% error range shown as a pale blue band about that line. The total temperature
     increase from the period 1850 to 1899 to the period 2001 to 2005 is 0.76°C± 0.19°C (1.37°F ± 0.34°F).
    Land regions have warmed at a faster rate than the oceans. Warming has occurred in both land and
    oceans  and in both sea surface temperature (SST) and nighttime marine air temperature over the
    oceans. However, for the globe as a whole, surface air temperatures over land have risen at about
    double  the ocean rate  after 1979 (more than 0.27°C per decade vs. 0.13°C per  decade), with the
    greatest warming during winter (December to February) and spring (March to May) in the Northern
    Hemisphere. Recent warming is strongly evident at all latitudes in SSTs over each of the oceans.
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•   Average Arctic temperatures increased at almost twice the global average rate in the past 100 years.
    Arctic temperatures have high decadal variability, and a warm period was also observed from  1925 to
    1945.

•   Between 1901 and 2005, warming is statistically significant over most of the world's surface with the
    exception of an area south of Greenland and three smaller regions over the southeastern U.S. and
    parts of Bolivia and the Congo basin. The lack of significant warming at about 20% of the locations,
    and the  enhanced warming in other places, is  likely  to be  a result of changes in atmospheric
    circulation.  Warming is strongest  over the  continental interiors  of Asia and northwestern North
    America and over some  mid-latitude  ocean regions  of the Southern  Hemisphere  as well as
    southeastern Brazil.

•   Since 1979, warming has been strongest over western North America, northern Europe and China in
    winter, Europe and northern and eastern Asia in spring, Europe and North  Africa in summer and
    northern North America, Greenland and eastern Asia in autumn.

Box 4.1: Updated Global Surface Temperature Trends through 2008

The global surface temperature trend  analysis in IPCC (2007a)  includes data  through  2005.   Three
additional years of data have become available  since then  (2006-2008).  According to NOAA's 2008
State of the Climate Report (NOAA, 2009a):

    •    Eight of the ten warmest years on record have occurred since 2001.

    •    The year 2008 tied with 2001 as the eighth warmest year on record for the Earth. The combined
        global  land and ocean surface temperature from January-December was 0.88 degree F  (0.49
        degree C) above the 20th Century average of 57.0 degrees F (13.9 degrees  C).

    •    Since 1880, the annual combined global  land and ocean surface temperature has  increased at a
        rate of 0.09 degree F  (0.05 degree C)  / decade.  This rate has increased  to 0.29 degree F (0.16
        degree C) / decade over the past 30 years.

Data analyzed by NASA through 2008  show similar trends (NASA, 2009).  It found 2008 was the ninth
warmest year in the period of instrumental measurements, which extends back to  1880. In both analyses
1998 and 2005 remain the two warmest years on record.
Global Upper Air Temperatures

Temperature measurements have also been made above the Earth's surface over the past 50 to 60 years
using radiosondes  (balloon-borne  instruments) and  for  the  past  28  years using  satellites. These
measurements support the analysis of trends and variability in the troposphere (surface to 10-16 km) and
stratosphere (10-50 km above the earth's surface).

The U.S. Climate Change Science Program prepared a report which assessed temperature changes in the
atmosphere, differences in these changes at various levels in the atmosphere, and our understanding of the
causes of these changes and differences. It concluded (Wigley et al., 2006): ".. .the most recent versions
of all available data sets show that both the  surface and troposphere have warmed, while the stratosphere
has cooled. These changes are in accord with our understanding of the effects of radiative forcing agents
and with the results from model simulations."
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The IPCC (Trenberth et al., 2007) re-affirmed the major conclusions of this CCSP report finding:

•  New analyses of radiosondes and satellite measurements of lower- and mid-tropospheric temperature
   show warming rates that are similar to those of the surface temperature record and are consistent
   within their respective uncertainties.

•  The satellite tropospheric temperature record is broadly consistent with surface temperature trends.
   The range (due to different data sets) of global surface warming since 1979 is 0.16°C to 0.18°C per
   decade  compared to 0.12°C to 0.19°C per  decade for estimates  of tropospheric temperatures
   measured by satellite.

•  Lower-tropospheric temperatures measured by radiosondes have slightly greater warming rates than
   those at the surface over the period 1958 to 2005. The radiosonde record is markedly less spatially
   complete than the surface record and increasing evidence suggests that it is very likely that a number
   of records have a cooling bias, especially in the tropics.

Lower stratospheric temperatures have cooled since 1979. Estimates from adjusted radiosondes, satellites
and re-analyses are in qualitative agreement, suggesting a lower-stratospheric cooling of between 0.3°C
and 0.6°C per decade since 1979.

The global upper air temperature trend analysis in IPCC (2007a) described above includes data through
2005.  Three  additional years of data have become available since then (2006-2008).  The addition of
these three years does not significantly alter the above trends. For example, in NOAA (2009) the satellite
tropospheric temperature trend computed through 2008 ranges from  + 0.11°C to + 0.15°C  per decade
compared to the estimate of + 0.12°C to + 0.19°C per decade given in IPCC (2007a).
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                             Figure 4.3: Reconstructions of (Northern Hemisphere average or
                             global average) surface temperature variations from six research
                             teams
                                0.6
                                                                                             --0.2
                                                                                             --0.4
                                -1.2
                                                                                             --0.6
                                                                                             --0.8
                                                                                             --1.0
                                                                                              -1.2
                                  900
                                                                                      1900
Global Surface
Temperatures Over the
Last 2,000 Years

Instrumental       surface
temperature  records only
began  in  the   late  19th
century,      when      a
sufficiently  large   global
network of measurements
was  in  place to  reliably
compute   global    mean
temperatures.  To estimate
temperatures  further back
in time, scientists  analyze
proxy   evidence    from
sources such as tree  rings,
corals,   ocean  and  lake
sediments,  cave  deposits,
ice    cores,    boreholes,
glaciers, and  documentary
evidence.      A   longer
temperature   record  can
help place the 20th century
warming  into a  historical
context.

The  National   Research
Council conducted a study
to describe and assess the  state of scientific efforts to reconstruct surface temperature records for the Earth
over approximately the last 2,000 years and the implications of these efforts for our understanding of
global climate change. It found (NRC, 2006b):

•   Large-scale  surface  temperature reconstructions, as illustrated  in Figure 4.3, yield a generally
    consistent picture of temperature trends during the preceding millennium, including relatively warm
    conditions centered around A.D. 1000 (identified by some as the "Medieval Warm Period") and a
    relatively cold period  (or "Little Ice Age") centered around 1700.

•   It can be said with a high level of confidence that  global mean surface temperature was higher during
    the last few decades of the 20th century than during any comparable period during the preceding four
    centuries.   The observed warming in the instrumental record shown in Figure  4.2  supports this
    conclusion.

•   Less confidence can be placed in large-scale surface  temperature reconstructions for the period from
    A.D. 900 to 1600. Presently available proxy evidence indicates that temperatures at many, but not all,
    individual locations were higher during the past 25 years than during any period of comparable length
    since A.D. 900. The uncertainties associated with reconstructing  hemispheric mean or global mean
    temperatures  from these data increase substantially backward in time through this period and are not
    yet fully quantified.
                                     Borehole temperatures (Huang et al. 2000) —Glacier lengths (Oerlemans 2005)
                                   —Multiproxy (Mann and Jones 2003)       —Multiproxy (Moberg et al. 2005)
                                     Multiproxy (Hegerl et al. 2006)          —Tree rings (Esper et al. 2002)
                                   —Instrumental record (Jones et al. 2001)

                             Source: NRC (2006b) Reconstructions of (Northern Hemisphere average or global
                             average) surface temperature variations from six research teams (in different color
                             shades) along with the instrumental record of global average surface temperature
                             (in black). Each curve illustrates a somewhat different history of temperature
                             changes, with a range of uncertainties that tend to increase backward in time (as
                             indicated by the shading).
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•   Very little confidence can be assigned to statements concerning the hemispheric mean or global mean
    surface temperature prior to about A.D.  900 because of sparse data  coverage  and because the
    uncertainties associated with proxy data and the methods used to analyze and combine them are larger
    than during more recent time periods.

Considering this study and additional research, the IPCC (2007d) concluded:  "Paleoclimatic information
supports the interpretation that the warmth of the last half century is unusual in at least the previous 1,300
years."

4(c)   U.S. changes in temperatures

Like global mean temperatures, U.S. temperatures also warmed during the 20th and into the 21st century.
According to NOAA (2009b) and data from NOAA15:

•   U.S. average annual temperatures are now approximately 1.25°F (0.69°C) warmer than at the start of
    the 20th century, with an increased rate of warming over the past 30 years. The rate of warming for
    the entire period of record  (1895-2008) is 0.13°F/decade while  the rate of warming increased to
    0.58°F/decade (0.32°C/decade) for the period from 1979-2008.

•   2005-2007 were exceptionally warm years (among the top 10 warmest on record), while 2008 was
    slightly warmer than average (the 39th warmest year on record), 0.2°F (0.1°C) above the 20th century
    (1901-2000) mean.

•   The last ten 5-year periods (2004-2008, 2003-2007, 2002-2006, 2001-2005, 2000-2004, 1999-2003,
    1998-2002,  1997-2001, 1996-2000, and 1995-1999), were the warmest 5-year periods (i.e. pentads) in
    the 114 years of national records, demonstrating the anomalous warmth of the last 15 years.
15 Data obtained from NOAA's National Climatic Data Center. Data may be downloaded from:
http://www.epa.gov/climatechange/anpr/data.html (see file: AnnualUSTemp_through 2008.xls)
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Regional data analyzed from NOAA's
National Climatic Data  Center  U.S.
Historical     Climate     Network16
(USHCN),  as illustrated in Figure 4.4,
indicate    warming   has    occurred
throughout most of the  U.S., with all
but three of the eleven climate regions
showing an increase  of more than 1°F
since  1901  through 2006  (NOAA,
2007). As  shown in Figure 4.4, the
greatest temperature  increase occurred
in Alaska  (3.3°F per century).  The
Southeast shows  essentially no trend
over the entire period, but has warmed
since 1979.

Including all of North America in its
assessment  of regional  temperatures,
the IPCC (Field et al, 2007) stated:

•   For  the  period  1955-2005,  the
    greatest  warming   occurred   in
    Alaska and north-western Canada,
    with substantial  warming  in  the
    continental interior  and  modest
    warming in the south-eastern U.S.
    and eastern Canada.

•   Spring   and   winter  show   the
    greatest changes in temperature and
    daily    minimum    (night-time)
    temperatures  have warmed more
    than daily  maximum  (daytime)
    temperatures.
Figure 4.4: Map of the United States, depicting regional
U.S. temperature trends for the period 1901 to 2006.
       Northwest
   Wesl
North Central           Central
     i       East
     I    North Central
Northeast
         Wesl
          Soilhwwt
                        Alaska
           Temperature change f F percenliry):
            -3-2-1    0    1    23
                Gray interval:-0,1 to0.1°F

 Red shades indicate warming over the period and blue shades
 indicate cooling over the period.
4(d)   Global changes in precipitation

A consequence of rising temperature is increased evaporation, provided that adequate surface moisture is
available (e.g., over the oceans and other moist surfaces).  The average atmospheric water vapor content
has increased since at least the 1980s over land and ocean as well as in the upper troposphere (IPCC,
2007d). When evaporation increases, more water vapor is available for precipitation producing weather
systems  leading to  precipitation increases  in  some areas.  Conversely, enhanced  evaporation  and
evapotranspiration  from warming accelerates land surface drying and increases the  potential incidence
and severity of droughts in other areas.
16 Data for map obtained from NOAA's National Climatic Data Center. Data may be downloaded from:
http://www.epa.gov/climatechange/anpr/data.html (files are: CONUS mean temp anomaly 2.5X3.5_through
2006.xls and AK-HI mean temp anomaly_through 2006.xls)
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Observations  show  that  changes are  occurring  in the amount, intensity,  frequency  and type  of
precipitation. According to the IPCC (Trenberth et al., 2007):

•   Long-term trends from 1900 to 2005 have been observed in precipitation amount over many large
    regions. Significantly increased precipitation has been observed in eastern  parts of North and South
    America, northern Europe and northern and central Asia. Drying has been observed in the  Sahel, the
    Mediterranean, southern Africa and parts of southern Asia. Precipitation is highly variable spatially
    and temporally, and data are limited in some regions.

•   More intense and longer droughts have been observed over wider areas since the 1970s, particularly
    in  the  tropics and  subtropics.  Increased drying linked  with higher temperatures and  decreased
    precipitation has contributed to changes in drought. The regions where droughts have occurred seem
    to  be determined largely by changes in sea  surface temperatures  (SSTs),  especially in the tropics,
    through associated changes in the atmospheric  circulation and precipitation.  Decreased  snowpack
    and snow cover have also been linked to droughts.
•   It  is  likely  that  there  have  been
    increases  in  the number of heavy
    precipitation   events   (e.g.,   95th
    percentile) within many land regions,
    even in those where there has been a
    reduction   in   total   precipitation
    amount, consistent  with  a  warming
    climate   and   observed  significant
    increasing amounts of water vapor in
    the atmosphere.

•   Rising temperatures have generally
    resulted in rain  rather than snow in
    locations   and    seasons    where
    climatological average  (1961-1990)
    temperatures were close to 0°C.

4(e)   U.S. changes in precipitation

Data  analyzed from NOAA's  National
Climatic   Data  Center  U.S.  Historical
Climate Network  (USHCN)17 show that
over the  contiguous U.S.,  total  annual
precipitation increased at an average rate
of 6.5% per century  from 1901-2006. As
shown in Figure 4.5, the greatest increases
in precipitation were in the  East North
Central    climate   region   (11.2%   per
century)   and   the   South   (10.5%).
Precipitation in the Northeast increased by
Figure 4.5: Map of the United States, depicting
precipitation trends for the contiguous U.S. 1901-2006,
Hawaii 1905-2006 and Alaska 1918-2006.
         North west
  West
North Central
          East
        North Central
Central
   Northeast
           West
             Change In precipitation (% per century):
             I	I
           -35-28-21-14 -7  0  7 14 21 28 35
                    Grav interval:-2 to 2%
Green shades indicate a trend towards wetter conditions over the
period, and brown shades indicate a trend towards dryer conditions.
No data are available for areas shaded in white.
17 Data for maps obtained from NOAA's National Climatic Data Center. Data may be downloaded from:
http://www.epa.gov/climatechange/anpr/data.html (files are: CONUS precip anomaly 2.5X3.5_through 2006.xls and
AK-HI precip anomaly_through 2006.xls)
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8.3%, in the Southeast by  1.9%,  the  Central U.S. by 8.1%, the West North Central by  1.9%,  the
Southwest by 1.3%, the West by 9.1%, and the Northwest by 6.0%.

Outside the contiguous U.S., Alaska experienced a precipitation increase of about 5.9% per century (since
records  began in 1918) and Hawaii experienced a decrease of 7.2% per century (since records begin in
1905).

Despite the overall national trend towards wetter conditions, a severe drought has affected the southwest
U.S. from 1999 through 2008 (see  Section 4(1)) which is indicative of significant variability in regional
precipitation patterns overtime and space.

4(f)     Global sea level rise

There is strong evidence that global sea level gradually rose in the 20th century  and is currently rising at
an increased rate, after a period of little change between AD 0 and AD 1900 (IPCC, 2007a).

According  to Bindoff et al. (2007), there is  high confidence that the rate of sea level rise increased
between the mid-19th and mid-20th centuries. The average rate of sea level rise measured by tide gauges
from 1961 to 2003 was 1.8 ± 0.5 mm per year (Bindoff et al., 2007). The global average rate of sea level
rise measured by satellite altimetry  during 1993 to 2003 was 3.1 ±0.7 mm per year (Bindoff et al., 2007).
Coastal tide gauge measurements confirm this observation. It is unclear whether the faster rate for 1993 to
2003 is  a reflection of short-term variability or an increase in the longer-term trend (Bindoff et al., 2007).
The total 20th century sea level rise is estimated to be 0.17 ± 0.05 m (Bindoff et al., 2007).

Two major processes lead to changes in global mean  sea level on decadal and longer time scales: i)
thermal expansion, and ii) the exchange of water between oceans and other reservoirs  (glaciers and ice
caps, ice sheets, and other land water reservoirs). It is believed that on average, over the period from
1961 to 2003, thermal expansion contributed about one-quarter  of the observed sea  level rise, while
melting of land ice accounted for less than half; the full magnitude of the observed sea level rise was not
satisfactorily explained by the available data sets (Bindoff et al., 2007). During this period, global ocean
temperature rose by 0.10°C from the surface to a depth of 700 m, contributing an average of 0.4 ±0.1 mm
per year to sea level rise (Bindoff et al., 2007).  The contribution from ice was  approximately 0.7 ± 0.5
mm per year (Lemke et al., 2007).

For recent years (1993-2003) for which the observing system is  much  better, thermal expansion and
melting of land ice each account for about half of the observed sea level  rise, although there is some
uncertainty in the estimates. Thermal expansion contributed about 1.6 ± 0.5 mm per year, reflecting a
high rate of warming for the period relative to 1961 to 2003  (Bindoff et al., 2007). The total contribution
from melting ice to sea level change between 1993 and 2003 ranged from 1.2 ± 0.4 mm per year. The rate
increased over the 1993 to 2003 period primarily due to increasing losses from mountain glaciers and ice
caps,  from increasing surface  melt on the Greenland Ice Sheet  and from  faster flow of parts of the
Greenland and Antarctic Ice Sheets  (Lemke et al., 2007).

Thermal expansion  and exchanges of water between oceans and other reservoirs cause changes in the
global mean as well as geographically non-uniform sea level change. Other factors influence changes at
the regional scale, including changes in ocean circulation or atmospheric pressure, and geologic processes
(Bindoff et al., 2007). Satellite measurements (for the period 1993-2003) provide unambiguous evidence
of regional variability of sea level change (Bindoff et al., 2007). In some regions, rates of rise have been
as much as several times the global mean, while sea level is falling  in other regions. According to IPCC
(Bindoff et al.,  2007), the largest sea level rise since  1992 has taken place in  the western Pacific and
eastern Indian Oceans, while nearly all of the Atlantic Ocean shows sea level rise during the past decade
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with the rate of rise reaching a maximum (over 2 mm yr1) in a band running east-northeast from the U.S.
east coast. Sea level in the eastern Pacific and western  Indian Oceans has been falling.

4(g)   U.S. sea level rise

Sea level18 has been rising  0.08-0.12 inches per year  (2.0-3.0 mm per year) along most of the U.S.
Atlantic and Gulf coasts. The rate of sea level rise varies from about 0.36 inches per year (10 mm per
year) along the Louisiana Coast (due to land sinking), to a drop of a few inches per decade in parts of
Alaska (because land is rising). Records from the coast of California indicate that sea levels have risen
almost 18 cm  during the past century (California Energy Commission, 2006).  According to the  CCSP
(2009b), in the mid-Atlantic region from New York to North Carolina, tide-gauge observations indicate
that relative sea-level rise (the combination of global sea-level rise and land subsidence) rates were higher
than the global mean and generally ranged between 2.4 and 4.4 millimeters per year, or about 0.3 meters
(1 foot) over the twentieth century.

Rosenzweig et al. (2007) document studies that find 75% of the shoreline removed from the influence of
spits, tidal inlets and engineering structures is eroding  along the U.S. East Coast probably due to sea level
rise. They also cite studies reporting losses in coastal wetlands observed in Louisiana, the mid-Atlantic
region, and in parts of New England and  New  York, in spite  of recent  protective  environmental
regulations.

4(h)   Global ocean acidification

Ocean waters can absorb large amounts of CO2 from the atmosphere, because the gas is weakly acidic and
the minerals dissolved in the ocean have over geologic time created a slightly alkaline  ocean, with surface
pH ranging from 7.9 to 8.25.  The amount of carbon contained in the oceans has increased due  to the
elevated atmospheric pressure of CO2 from anthropogenic  emissions (Denman et  al.,  2007).   IPCC
estimates that the total  inorganic carbon content of the oceans increased by 118 ± 19  GtC between 1750
and 1994  and  continues to  increase (Bindoff et al., 2007).  This absorptive capacity of the oceans has
resulted in atmospheric CO2 concentrations substantially lower than they otherwise would be.  Since the
beginning of the industrial revolution, sea surface pH has dropped by about 0.1 pH units, corresponding
to a 30% increase in the concentration of hydrogen ions (Denman et al., 2007).

Ocean acidification is causing a series of cascading changes to the chemistry of ocean water, including a
decrease in the saturation state of calcium carbonate. Marine calcifiers, such as corals, are dependent
upon this  mineral  to form  shells,  skeletons, and other  protective  structures.   Reduced  availability of
calcium carbonate  can slow or even halt calcification  rates amongst these organisms (Fischlin  et al.,
2007).  The availability of carbonate is also important because it controls the maximum amount of CO2
that the ocean is  able to absorb (Bindoff et al. 2007, p. 406).   More information regarding  ocean
acidification projections  and impacts  to  marine  ecosystems  can be found in sections 6(b) and  14(a),
respectively.  It  is  important to note that ocean acidification is a direct consequence of fossil  fuel CO2
emissions, which are also the main driver of the anticipated climate change (Denman et al., 2007).

4(i)   Global changes in physical and biological systems

Physical and biological systems on all continents and in most oceans are already being affected by  recent
climate changes, particularly regional temperature increases (very high confidence) (Rosenzweig.  et al.,
2007).  Climatic effects on human systems, although more difficult to discern due to adaptation and non-
18 U.S. sea level data obtained from the Permanent Service for Mean Sea Level < http://www.pol.ac.uk/psmsl/> of
the Proudman Oceanographic Laboratory.

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climatic drivers, are emerging (medium confidence) (Rosenzweig. et al., 2007). The majority of evidence
comes from mid-  and high latitudes in the Northern Hemisphere,  while  documentation of observed
changes in tropical regions and the Southern Hemisphere is sparse (Rosenzweig. et al., 2007). Hence, the
findings presented in this section  apply generally to the  globe but most directly  to Europe and North
America (including the U.S.) where these observational studies were conducted.  The  extent to which
observed changes discussed here  can  be attributed to anthropogenic  GHG emissions is discussed in
Section 5.

Cryosphere (Snow and Ice)

Observations of the cryosphere (the "frozen" component of the climate system) have revealed changes in
sea ice, glaciers and snow cover, freezing and thawing, and permafrost.  According  to IPCC, the
following physical changes have been observed:

Satellite data since 1978 show that annual average  Arctic sea ice  extent has shrunk by  2.7 ± 0.6 % per
decade, with larger decreases in summer of 7.4 ± 2.4% per decade. The latest data from NASA indicate
Arctic sea ice  set a record low in September 2007, 38 percent below the  1979-2007  average (NASA
Goddard Space Flight Center, 2007). The extent of the sea ice loss between 1979 and 2007  can be seen in
Figure 4.6.  In September 2008,  Arctic sea ice reached its second lowest extent on record (NASA
Goddard Space Flight Center,  2008).   The size and  speed of recent summer sea ice loss  is highly
anomalous relative to the previous few thousands of years (Polyak et al., 2009).

Figure 4.6 Arctic Sea Ice Concentrations Comparisons
                     1979                                           2007
These two images, constructed from satellite data, compare arctic sea ice concentrations in September of 1979 and
2007 (Images courtesy of NASA).

•   Antarctic sea ice extent shows no statistically significant average trends according to IPCC (2007d).
    However, the U.S. National and Snow and Ice Data Center states that Antarctic sea ice underwent a
    slight increase from 1979 to 2007 (NSIDC, 2009).

•   The average sea ice thickness in the central Arctic has very likely decreased by up to 1 m from 1987
    to 1997, based upon submarine-derived data.  Model-based reconstructions support this, suggesting
    an arctic-wide reduction of 0.6 to 0.9 m over the same period (Lemke et al., 2007).

•   Mountain glaciers  and snow cover have declined on average  in both  hemispheres.   Northern
    hemisphere snow cover observed by satellite over the 1966 to 2005 period decreased in every month
    except November and December, with a stepwise drop of 5% in the annual mean in the late  1980s. In
    the Southern Hemisphere, the few long records or proxies mostly show either decreases or no changes
    in the past 40 years or more.  The strongest mass losses of mountain glaciers (per unit area) have been
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    observed in  Patagonia, Alaska and the northwestern U.S.  and southwest Canada. Because of the
    corresponding large areas, the biggest contributions to sea level rise came from Alaska, the Arctic and
    the Asian high mountains (Lemke et al., 2007).

•   Freeze-up date  for river and lake ice has  occurred  later at a rate of 5.8 ± 1.6 days per century,
    averaged over available data for the Northern Hemisphere spanning the past 150 years. Breakup date
    has occurred earlier at a rate of 6.5 ±1.2 days per century (Lemke et al., 2007).

•   Temperatures at the top of the permafrost layer have generally increased since the 1980s in the Arctic
    (by up to 3°C).  The permafrost  base has been thawing at  a rate ranging up to 0.04 m per year in
    Alaska since 1992 and 0.02 m per year on the Tibetan Plateau since the 1960s. The maximum area
    covered  by seasonally frozen ground has decreased by 7%  in the Northern Hemisphere since 1900,
    with a decrease in spring of up to  15% (Lemke et al., 2007).

There are  additional effects related  to changes in the cryosphere.  Melting of highly reflective snow and
ice reveals darker land and ocean surfaces, creating a positive feedback that increases absorption of the
sun's heat and further warms the planet. Increases in glacial melt and river runoff add more freshwater to
the ocean, raising global sea level.

Hydrosphere

The term  "hydrosphere"  refers to the component of the  climate system  comprising liquid  surface and
subterranean water,  such as rivers, lakes, and underground water.  Several changes in these features have
been observed, as summarized by the IPCC (Rosenzweig et al., 2007):

•   Documented trends in severe  droughts and  heavy  rains  show that hydrological  conditions are
    becoming more  intense in some regions.  Globally, very dry areas (Palmer Drought Severity Index—
    PDSI—less than or equal to -3.0)  have more than doubled since the 1970s due to a combination  of El
    Nino-Southern Oscillation  events and surface warming.  Very wet areas (PDSI greater than or equal
    to +3.0) declined by  about 5% since the 1970s, with precipitation as the major contributing factor
    during the early 1980s and temperature more important thereafter.  The areas of increasing wetness
    include the Northern Hemisphere high latitudes and equatorial regions.

•   Climate  change  signals related to  increasing runoff and stream flow have been observed over the last
    century  in many regions, particularly in basins fed by glaciers, permafrost, and snowmelt. Evidence
    includes increases in  average  runoff of Arctic rivers in Eurasia, which has  been at  least partly
    correlated with  climate warming, and earlier spring  snowmelt and increase in winter base flow in
    North America and Eurasia due to enhanced seasonal snow melt associated with climate warming.

•   Freshwater lakes and rivers are  experiencing increased water temperatures and changes in water
    chemistry. Surface and deep lake-waters are warming, with advances and lengthening of periods of
    thermal  stability in some cases associated with physical and chemical changes such as increases in
    salinity  and  suspended solids, and a decrease in nutrient content.  Lake  formation and subsequent
    disappearance in permafrost have been reported in the  Arctic.

Changes  in  river discharge as well as in droughts and  heavy rains  in  some  regions indicate that
hydrological conditions have become more intense but significant trends in floods and in evaporation and
evapotranspiration have not been detected globally. Some local trends in  reduced groundwater and lake
levels have been  reported, but studies have been unable to  separate the effects of variations in temperature
and precipitation from the effects of human interventions  such as groundwater management (Rosenzweig
et al., 2007).
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Biosphere

According to IPCC, terrestrial ecosystems and marine and freshwater systems show that recent warming
is strongly affecting natural biological systems (very high confidence) (Rosenzweig et al, 2007):

•   The overwhelming majority of  studies  of regional climate effects on  terrestrial  species reveal
    consistent responses to warming trends, including poleward and elevational range shifts of flora and
    fauna.   Changes  in  abundance  of certain species, including  limited  evidence  of a  few local
    disappearances, and changes  in  community composition over the  last few decades  have been
    attributed to climate change.

•   Responses of terrestrial species to warming across the northern hemisphere are well documented by
    changes in the  timing of growth stages, especially the earlier onset of spring events, migration, and
    lengthening of the growing season.  Changes in phenology (the  timing  of annual  phenomena  of
    animal and plant life) include  clear temperature-driven  extension of the growing season by up to 2
    weeks in the second half of the 20th century in mid- and high northern latitudes, mainly due to  an
    earlier spring, but partly due also to a later autumn.  Egg-laying dates have advanced in many bird
    species, and many small mammals have been found to come out of hibernation and to breed earlier in
    the spring now  than they did a few decades ago.

•   Many observed changes in phenology and distribution of marine species have been associated with
    rising water temperatures,  as well as other climate-driven changes in salinity, oxygen  levels, and
    circulation. For example, plankton has moved poleward  by 10° latitude over a period of 4 decades in
    the North Atlantic. While  there is increasing evidence for climate change  impacts on coral reefs,
    discerning the impacts of climate-related stresses from other stresses (e.g. over fishing and pollution)
    is difficult. Warming of lakes and  rivers is affecting  abundance  and  productivity, community
    composition, phenology, distribution and migration of freshwater species (high confidence).

4(j)    U.S. changes in physical and biological systems

Many of the global changes in physical  and biological systems mentioned in  4(h) broadly apply to the
U.S.  Some  U.S.-specific changes in these  systems cited in IPCC's Fourth Assessment  Report are
described in this subsection, as well as in section 1 l(a) for physical systems related to water resources and
section 14(a) related to biological systems. Of all the observed changes to physical systems assessed by
IPCC (Rosenzweig et al., 2007) for North America (totaling 355),  94%  of them  were consistent with
changes one  would expect  with average warming.  Similar consistency  was found between observed
biological system changes and warming for North America (see discussion below under biosphere).

Furthermore, a CCSP (2008e) assessment reported that climate changes are very likely  already affecting
U.S. water resources, agriculture, land resources, and biodiversity as a result of climate  variability and
change.  It found, "The number and frequency of forest fires  and insect outbreaks are  increasing in the
interior  West, the Southwest,  and Alaska.  Precipitation, streamflow,  and  stream  temperatures are
increasing in most  of the continental  United  States. The western United States is experiencing reduced
snowpack and earlier peaks in  spring runoff.  The growth of many crops and weeds is being stimulated.
Migration of plant  and animal  species is changing  the composition and structure of arid, polar, aquatic,
coastal, and other ecosystems" (Backlund et al., 2008a)

Additional  findings  from  this CCSP  assessment  along  with  results  presented in  IPCC's  Fourth
Assessment Report are described below.

Cryosphere (Snow and Ice)
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In North America, from 1915 to 2004, snow covered area increased in November, December and January
due to increases in precipitation. However, snow  cover decreased  during the latter half of the 20th
century, especially during the spring over western North America (Lemke et al., 2007). Shifts towards
earlier melt by about eight days since the mid-1960s were also observed in northern Alaska (Lemke et al.,
2007). Consistent with these findings, Lettenmaier et al. (2008) note a trend toward reduced mountain
snowpack, and earlier spring snowmelt runoff peaks across much of the western U.S.

The IPCC (Lemke et al., 2007) cites a study documenting glacier mass balance loss in the northwest U.S.
and Alaska, with losses especially rapid in Alaska after the mid-1990s. Rosenzweig et al. (2007) refer to
a study documenting evidence of present crustal uplift in response to recent glacier melting in Alaska.

Hydrosphere

Lettenmaier et  al. (2008) document increases  in U.S. streamflow during the second half of the 20th
century consistent with increases in precipitation described in 4(e).

Rosenzweig et  al. (2007) indicate surface water temperatures have warmed by  0.2 to  2°C in lakes and
rivers in North  America since the 1960s. They also discuss evidence for an earlier occurrence of spring
peak river flows and an increase in winter  base flow in basins with important  seasonal snow cover in
North America.

Biosphere

The IPCC (Rosenzweig  et al., 2007) assessed a multitude of studies that  find changes in terrestrial
ecosystems and marine and freshwater systems in North America.  Of 455  biological observations
assessed from these studies, 92% were consistent with the changes expected due to average warming.

Backlund et al.  (2008a) find:

    •   There has been a significant lengthening of the growing season and increase in net primary
       productivity (NPP) in the  higher latitudes  of North America. Over the  last 19 years, global
       satellite data indicate an earlier onset of spring across the temperate latitudes by  10 to 14 days.

    •   In an analysis of 866  peer-reviewed papers exploring the ecological consequences  of climate
       change, nearly 60 percent of the 1598 species studied exhibited shifts in their distributions and/or
       phenologies over the 20- and 140-year time frame.

    •   Subtropical  and tropical corals in shallow waters have already suffered major bleaching events
       that are clearly driven by increases in sea surface temperatures.

In addition, Ryan et al. (2008) note, "Climate change has very likely increased the  size and  number of
forest fires, insect outbreaks, and tree mortality in the interior west, the Southwest, and Alaska."

4(k)   Global  extreme events

Climate is defined not simply as average temperature and precipitation but also by  the type, frequency
and intensity of extreme  events. The IPCC  documents observed changes  in climate  extremes related to
temperature, precipitation, tropical cyclones, and sea level. The changes described apply generally to all
parts of the globe,  including the U.S., although there are some  regional and local exceptions due to
patterns of natural climate variability.   Current observations are summarized here, projected trends are
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covered in Section 6, and the sectoral impacts of these changes are covered as relevant in Sections 7 to
15.

Temperature

Widespread changes in extreme temperatures have been observed in the last 50 years.  Cold days, cold
nights, and frost have become less frequent, while hot days, hot nights, and heat waves have become more
frequent (IPCC, 2007d). A widespread reduction in the number of frost days in mid-latitude regions, an
increase in the number of warm extremes  and a reduction in the number of daily cold extremes are
observed in 70 to 75% of the land regions where data are available. The most marked changes are for cold
(lowest 10%, based on 1961-1990)  nights, which have become rarer over the 1951 to 2003 period. Warm
(highest 10%) nights have become more frequent.

Precipitation and Storms

It is likely that there have been increases in the number of heavy precipitation events19 within many land
regions, even in those where there  has been a reduction in total precipitation amount, consistent with a
warming  climate and  observed significant increasing amounts  of water vapor in the  atmosphere.
Increases have also been reported for rarer precipitation events (1 in 50 year return period), but only a few
regions have sufficient data to assess such trends reliably (Trenberth et al., 2007).

More intense and longer droughts have been observed over wider areas since the 1970s, particularly in the
tropics and subtropics (IPCC, 2007d).   Increased drying linked with higher temperatures and decreased
precipitation has contributed to changes in drought (IPCC, 2007d).

The CCSP (2008i) report on extreme events, in its section on  tropical cyclones  (i.e. tropical storms and
hurricanes), states that there have been spatially inhomogeneous increases in the power dissipation index,
a measure of potential tropical cyclone  destructiveness, over the last few decades (Kunkel et al., 2008).
However, there remain reliability issues with historical data. Kunkel et al. (2008) refer to a study that was
not able to corroborate the presence of upward intensity trends over the last two decades in ocean basins
other than the North Atlantic. The report cautions that quantifying tropical cyclone  variability is limited,
sometimes seriously, by a large suite of problems with the historical record of tropical cyclone activity.
Correspondingly, there is no clear trend in the annual numbers of tropical cyclones (IPCC, 2007d).

High Sea Level

Apart from non-climatic events such as tsunamis, extreme sea levels occur mainly  in the form of storm
surges generated by tropical or extra-tropical cyclones.  There is evidence for an increase in extreme high
sea level since 1975 based upon an  analysis  of 99th percentiles of hourly sea level at 141  stations over the
globe (Bindoff et al., 2007).

4(1)     U.S. extreme events

Many of the global changes in extreme events mentioned in 4(j) broadly apply to the U.S.  Additionally,
the U.S. CCSP (2008i)  published a report that focused on changing climate extremes in the U.S. and
North America. It concluded (Karl  et al., 2008 in CCSP, 2008i):

    Many extremes and their associated impacts are now changing. For example, in recent decades most
    of North America has been experiencing more unusually hot days and  nights, fewer unusually cold
19
  Heavy precipitation events refer to those in the 95th percentile of precipitation events.
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    days and nights, and fewer frost days. Heavy downpours have become more frequent and intense.
    Droughts are becoming more severe in  some regions, though there are no clear trends for North
    America as a whole. The power and frequency of Atlantic hurricanes have increased substantially in
    recent  decades, though North American mainland land-falling hurricanes do  not  appear to have
    increased over the past century. Outside the tropics, storm tracks are shifting northward and the
    strongest storms are becoming even stronger.

Many of these changes were also assessed in IPCC's Fourth Assessment Report and are described in this
subsection.

Temperature

The IPCC (Trenberth et al., 2007) cites North America regional studies that all show patterns of changes
in temperature extremes consistent with a general warming.  Karl et al. (2008) find the number of heat
waves (extended periods of extremely hot weather) has been increasing over the past 50 years but note the
heat waves of the 1930s remain the most severe in the U.S. historical record.

Extreme cold has been decreasing.  Trenberth et al., 2007 cite a study finding intense  warming of the
lowest daily minimum temperatures over western and central North America. Trenberth et al. (2007)
caution the observed changes of the tails of the temperature distributions are often more complicated than
a simple shift of the entire distribution would suggest. Karl et al. (2008) note, "The last 10 years [1998-
2007] have seen fewer severe cold snaps than for any other 10-year period in the historical record, which
dates back to 1895." Karl et al. also indicate a decrease in frost days and a lengthening of the frost-free
season over the past century.

Precipitation and Storms

In the contiguous U.S., Trenberth et al. (2007) cite studies finding statistically significant increases in
heavy precipitation (the heaviest  5%) and very heavy precipitation (the heaviest 1%) of 14 and 20%,
respectively. Much of this increase occurred during the last three decades of the 20th century and is most
apparent over the eastern parts of the country. There  is also evidence from Europe and the U.S. that the
relative  increase in precipitation extremes is  larger than the increase in mean precipitation (Trenberth et
al., 2007).

Lettenmeir et  al. (2008)  find,  "With respect to  drought, consistent with streamflow and  precipitation
observations, most  of the  continental  United States experienced reductions in drought  severity and
duration over  the 20th century. However, there is  some indication of increased drought  severity and
duration in the western and southwestern United States...."

Diminishing snow pack and subsequent reductions in soil moisture appear to be factors in recent drought
conditions in the western U.S. (Trenberth et al., 2007). This drought has also been attributed to changes
in atmospheric circulation associated with warming of the western tropical Pacific and Indian oceans as
well as multidecadal fluctuations (Trenberth et al., 2007).

Karl et al. (2008) indicate a northward shift in the tracks of strong low-pressure systems (also known as
mid-latitude storms and/or extratropical cyclones) in both the North Atlantic and North Pacific over the
past fifty years with  increases in storm intensity noted in the Pacific (data inconclusive in the Atlantic).
Correspondingly, they also  find northward shift in snow storm occurrence, which is also consistent with
the warming temperatures and a decrease in snow cover extent over the U.S.
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IPCC (2007d) reports there is observational evidence for an increase in intense tropical cyclone (i.e.
tropical storms and/or hurricanes) activity in the North Atlantic (where cyclones develop that affect the
U.S.  East and Gulf Coasts) since about  1970,  correlated  with  increases of tropical  sea surface
temperatures.  Similarly, Kunkel et al.  (2008) conclude  (for the North Atlantic):  "There have been
fluctuations in the number of tropical storms and hurricanes from decade to decade, and data uncertainty
is larger in the early part of the record compared to the satellite era beginning in 1965. Even taking these
factors  into account,  it is  likely that the annual numbers of tropical storms, hurricanes, and major
hurricanes in the North Atlantic have increased over the past 100 years, a time in which Atlantic sea
surface temperatures also increased."

High Sea Level

Studies  of the longest records of extremes in sea level are  restricted to  a small number of locations.
Consistent with global  changes, U.S.-based studies  document increases  in extreme sea level closely
following the rise in mean sea level (Bindoff et al., 2007).
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Section 5

Attribution of Observed Climate Change to Anthropogenic Greenhouse Gas
Emissions at the Global and Continental Scale

This section addresses the extent to which observed climate change at the  global and continental or
national scale (described in Section 4) can be attributed to global anthropogenic emissions of GHGs.
Section 2 describes the share of the U.S. transportation sector to U.S. and global anthropogenic emissions
of GHGs, and the resultant share of U.S. transportation emissions to global increases in atmospheric
concentrations of GHGs.

Evidence of the effect of anthropogenic GHG emissions on the climate system, as well as climate-
sensitive systems and sectors, has increased over the last 15 years or so and even since the previous IPCC
assessment published  in 2001. The evidence in the  recent IPCC  Fourth Assessment Report (2007) is
based on analyses of global-  and continental-scale temperature  increases,  changes  in  other  climate
variables and physical and biological systems, and the radiative forcing caused by anthropogenic versus
natural factors.

5(a)   Attribution of observed climate change to anthropogenic emissions

Computer-based climate models are the primary tools used for simulating the  likely patterns of response
of the climate system to different forcing mechanisms (both natural and anthropogenic).  Confidence in
these  models comes  from their foundation in  accepted  physical principles  and from their ability to
reproduce observed features of current climate and past climate changes (IPCC, 2007a). For additional
discussion on the strengths and limitations of models, see  Section 6(b). Attribution studies evaluate
whether observed changes are  consistent  with  quantitative  responses  to  different forcings (from
greenhouse gases, aerosols and natural forcings such as changes solar intensity) represented in well-tested
models, and are not consistent with alternative physically plausible explanations.

Studies to detect climate change and attribute its causes using patterns of observed temperature  change
show  clear evidence of human influences on the climate system (Karl et al., 2006).  Discernible human
influences  extend to  additional aspects  of climate including ocean warming,  continental-average
temperatures, temperature extremes and wind patterns (Hegerl et al., 2007).

Temperature

IPCC statements on the linkage  between greenhouse gases and temperatures have strengthened since its
early assessments (Solomon et al., 2007).  The IPCC's First Assessment Report in 1990 contained little
observational evidence of a detectable  anthropogenic influence on climate (IPCC, 1990). In its  Second
Assessment Report in  1995, it stated the balance of evidence suggests a discernible human influence on
the climate of the 20th century (IPCC, 1996).  The  Third Assessment Report in 2001 concluded that most
of the observed warming over the last 50 years  is  likely to have been due to the  increase in greenhouse
gas concentrations (IPCC, 2001b). The conclusion in IPCC's 2007 Fourth Assessment Report (2007b) is
the strongest yet:

    Most of the observed increase  in global average temperatures since the mid-20th century  is very
    likely10 due to the observed increase in anthropogenic greenhouse gas concentrations.
20 According to IPCC terminology, "very likely" conveys a 90 to 99% probability of occurrence.  See Box 1.3 on
page 5 for a full description of IPCC's uncertainty terms.
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The  increased confidence in the greenhouse gas  contribution  to the observed  warming results from
(Hegerl. et al., 2007):

•   an expanded and improved range of observations allowing attribution of warming to be more fully
    addressed jointly with other changes in the climate system
•   improvements  in the simulation of many aspects  of present mean  climate and its variability on
    seasonal to inter-decadal time scales
•   more detailed representations of processes related to aerosol and other forcings in models
•   simulations of 20th-century climate change that use many more models and much  more complete
    anthropogenic and natural forcings
•   multi-model ensembles  that increase  confidence in attribution results by providing  an  improved
    representation of model uncertainty

Climate model simulations run by the IPCC, shown in Figure 5.1, suggest natural forcings alone cannot
explain the observed warming (for the globe, the global land and global ocean).  The observed warming
can only be reproduced with models that contain both natural and anthropogenic forcings.
Figure 5.1: Comparison of observed global-scale changes in surface temperature with
results simulated by climate models using natural and anthropogenic forcings.
              Global
  Global Land
Global Ocean
  IO.O
                               1.0

                               0.5

                               0.0
                     1.0

                     0.5

                     0.0
   1900
               1950
               Year
                          2000   1900
      1950
      Year
                                                       2000  1900
     1950
     Year
                                                                                   2000
           models using only
           natural forcings
models using both natural
and anthropogenic forcings
    observations
Source: IPCC (2007d).  Decadal averages of observations are shown for the period 1906 to 2005 (black
line) plotted against the centre of the decade and relative to the corresponding average for 1901-1950.
Lines are dashed where spatial coverage is less than 50%. Blue shaded bands show the 5-95% range
for 19 simulations from five climate models using only the natural forcings due to solar activity and
volcanoes. Red shaded bands show the 5-95% range for 58 simulations from 14 climate models using
both natural and anthropogenic forcings.
Additional evidence documented in the IPCC report supports its statement linking warming to increasing
concentrations of greenhouse gases (Hegerl et al., 2007):

•   Warming of the climate system has been detected in changes of surface and atmospheric temperatures
    in the upper several hundred meters of the ocean, and in contributions to sea level rise. Attribution
    studies have established anthropogenic contributions to all of these changes.
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•   Analyses of paleoclimate data have increased confidence in the role of external influences on climate.
    Coupled climate models used to predict future climate have been used to reproduce key features of
    past climates using boundary conditions and radiative forcing for those periods.

The IPCC states that it is very unlikely that the global pattern of warming observed during the past half
century is due to only known natural external causes (solar activity  and volcanoes) since the warming
occurred in both the atmosphere and ocean and took place when natural external forcing factors would
likely have produced cooling (Hegerl et al, 2007).  It also  states  greenhouse gas forcing  alone would
likely have resulted in warming greater than observed if there had not been an offsetting cooling effect
from aerosols and natural forcings during the past half century (Hegerl et  al., 2007).  Solomon et al.
(2007) indicate the sum of solar and volcanic forcing in the past half century  would likely have produced
cooling, not warming.       |—
                             Figure 5.2: Comparison of observed  North American changes in
                             surface temperature with results simulated  by climate models using
                             natural and anthropogenic forcings.
Not    only    has    an
anthropogenic  signal been
detected  for  the  surface
temperatures, but evidence
has also accumulated of an
anthropogenic    influence
through the vertical profile
of     the     atmosphere.
Fingerprint studies21  have
identified  greenhouse  gas
and sulfate aerosol signals
in    observed    surface
temperature   records,    a
stratospheric        ozone
depletion     signal     in
stratospheric temperatures,
and the combined effects
of these forcing agents in
the vertical structure   of
atmospheric    temperature
changes (Karl et al., 2006).
However,   an   important
inconsistency   may  have
been   identified  in   the
tropics. In the tropics, most
observational    data   sets
show  more warming at the
surface   than   in    the
troposphere,  while almost
all model simulations have
larger warming aloft  than at the surface.  A possible explanation for this  inconsistency is error in the
observations, but the issue is still under investigation (Karl et al., 2006).
                                               1900
                                      models using only
                                      natural forcings
                                                                                2000
models using both natural
and anthropogenic forcings
observations
                             Source: Hegerl et al. (2007).  Decadal averages of observations are shown for the
                             period 1906 to 2005 (black line) plotted against the centre of the decade and
                             relative to the corresponding average for 1901-1950. Lines are dashed where
                             spatial coverage is less than 50%. Blue shaded bands show the 5-95% range for
                             19 simulations from five climate models using only the natural forcings due to solar
                             activity and volcanoes. Red shaded bands show the 5-95% range for 58
                             simulations from 14 climate models using both natural and anthropogenic forcings.
21 Fingerprint studies use rigorous statistical methods to compare the patterns of observed temperature changes with
model expectations and determine whether or not similarities could have occurred by chance. Linear trend
comparisons are less powerful than fingerprint analyses for studying cause-effect relationships, but can highlight
important differences and similarities between models and observations (as in Figures 5.1 and 5.2).
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The substantial  anthropogenic  contribution to surface temperature increases likely applies  to  every
continent except Antarctica (which has insufficient observational coverage to make an assessment) since
the middle of the 20th century (Hegerl.  et  al., 2007).  Figure  5.2 indicates North America's  observed
temperatures over the last century can  only be reproduced using model simulations containing both
natural and anthropogenic forcings. In the CCSP (2008g) report "Reanalysis of Historical Climate Data
for Key Atmospheric  Features: Implications for Attribution of Causes of Observed Change", Dole et al.
(2008) find that for North America "more than half of this warming [for the period 1951-2006] is likely
the result of human-caused greenhouse gas forcing of climate change."

Difficulties remain in attributing temperature changes on smaller than continental scales and over time
scales  of less than 50 years. Attribution at these scales, with limited exceptions,  has  not  yet  been
established (Hegerl et al., 2007).

Temperature extremes have also likely been influenced by anthropogenic forcing. Many indicators of
climate extremes, including the annual numbers of frost days, warm and cold  days, and warm and cold
nights, show changes that are consistent with warming (Hegerl et al., 2007). An anthropogenic  influence
has been detected in some of these indices, and there is evidence  that anthropogenic forcing may have
substantially increased the risk of extremely warm  summer conditions  regionally,  such as  the 2003
European heat wave (Hegerl et al., 2007).  Karl et al. (2008) conclude the increase in human-induced
emissions of GHGs is estimated to have substantially increased the risk of a very hot year in  the U.S.,
such as that experienced  in 2006.  They add that other aspects of observed increases in temperature
extremes, such as changes in warm nights and frost days, have been linked to human influences.

Additional Climate Variables

There is  evidence of anthropogenic influence in other parts of the  climate system. The IPCC  noted the
following examples (Hegerl et al., 2007):

•   Trends over recent decades in the Northern and Southern Annular Modes22, which correspond to sea
    level pressure reductions over the  poles, are likely related in part to human activity, affecting storm
    tracks, winds and temperature patterns in both hemispheres. Models reproduce the sign  of the
    Northern Annular Mode trend,  but the simulated response is smaller than observed. Models  including
    both  greenhouse gas  and stratospheric ozone changes simulate  a realistic trend in  the  Southern
    Annular Mode, leading to a detectable human influence on global sea level pressure patterns.

It is more likely than not that anthropogenic influence has contributed to increases in the frequency of the
most intense tropical cyclones. Gutowski et al. (2008), as cited in the CCSP (2008i) report, likewise find
evidence suggesting a human contribution to recent hurricane activity. However, they caution that a
confident assessment  of human influence  on hurricanes will require further studies using models  and
observations, with emphasis on distinguishing natural from human-induced changes in hurricane activity
through their influence on factors such  as historical sea surface temperatures, wind shear, and atmospheric
vertical stability.

•   The latitudinal pattern of change in land precipitation and observed increases in heavy precipitation
    over  the 20th century appear to be consistent with the anticipated response to anthropogenic forcing.
22 Annular modes are preferred patterns of change in atmospheric circulation corresponding to changes in the
zonally averaged mid-latitude westerly winds. The Northern Annular Mode has a bias to the North Atlantic and has
a large correlation with the North Atlantic Oscillation (see footnote 36). The Southern Annular Mode occurs in the
Southern Hemisphere.
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Attributing changes in precipitation to anthropogenic forcing at continental or smaller scales is more
challenging. Clark et al. (2008) state that recent drought in the Southwest is consistent with projections of
increasing  subtropical aridity and recent trends in increasing precipitation intensity are also consistent
with projected trends. However, Clark et al. caution that there is considerable natural variability in the
hydroclimate in the Southwest and conclude that:  "There is no clear evidence to date of human-induced
global climate change on North American precipitation amounts."  Similarly, Karl et al. (2008) find heavy
precipitation events averaged over North America have increased over the past 50 years at a rate higher
than total precipitation  increased, consistent with the observed increases in atmospheric water vapor,
which have been associated with human-induced increases in greenhouse gases.

5(b)   Attribution of observed changes in physical and biological systems

In addition to attributing the observed changes in  average global- and continental-scale temperature and
other climate  variables  to anthropogenic GHG forcing,  a similar attribution can be made between
anthropogenic GHG forcing and observed changes in physical systems (e.g., melting glaciers) and
biological systems and species (e.g., geographic shift of species) which are shown to change as a result of
recent warming.

This section includes the observed changes  in physical and biological systems in North America and in
other parts of the world.

The IPCC  (2007b) concluded that, "Observational evidence from all continents and most oceans shows
that many natural systems  are being affected by regional climate changes,  particularly  temperature
increases." Furthermore, the IPCC states that, "A global assessment of data since  1970 has shown it is
likely that anthropogenic  warming has  had a discernible influence on  many physical and biological
systems." As detailed above in Section 5(a), recent warming of the  last 50 years is very likely the result
of the accumulation of anthropogenic GHGs in the  atmosphere.

Climate variability  and  non-climate drivers (e.g., land-use change, habitat fragmentation)  need to be
considered in  order to  make  robust conclusions about the role of  anthropogenic climate  change  in
affecting biological and physical systems.   IPCC  (Rosenzweig et al. 2007)  reviewed a number of joint
attribution studies that linked responses in some physical and biological systems directly to anthropogenic
climate change using climate, process, and statistical models. The conclusion of these studies is that "the
consistency of observed significant changes in physical and biological systems and  observed significant
warming across the globe  likely cannot  be  explained  entirely due to natural  variability or other
confounding non-climate factors (Rosenzweig et al. 2007)."

The physical systems undergoing  significant change include the cryosphere (snow  and ice systems),
hydrological systems, water resources, coastal zones  and the oceans.  These effects (reported with high
confidence by IPCC (Rosenzweig et al. 2007) include ground  instability in  mountain and permafrost
regions, shorter travel season for vehicles over frozen roads in the  Arctic, enlargement and increase of
glacial lakes in mountain regions and destabilization of moraines damming these lakes, changes in Arctic
flora  and fauna  including the sea-ice biomes and predators higher in the food chain,  limitations on
mountain sports in lower-elevation alpine areas, and changes in indigenous livelihoods in the Arctic.

Regarding biological systems, the IPCC (Rosenzweig et al. 2007) reports with very high confidence that
the overwhelming majority of studies of regional climate effects on terrestrial species reveal trends
consistent with warming, including poleward and  elevational range shifts of flora and fauna, the earlier
onset of spring events, migration, and lengthening of the growing season, changes in abundance of certain
species,  including  limited  evidence  of a few  local  disappearances,  and  changes  in   community
composition.
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Human system responses to climate change are more difficult to identify and isolate due to the larger role
that non-climate factors play (e.g., management practices in agriculture and forestry,  and adaptation
responses to protect human health against adverse climatic conditions) (Rosenzweig et al, 2007).
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Section 6
Projected Future Greenhouse Gas Concentrations and Climate Change

According to the IPCC (2007d),  "continued greenhouse gas emissions at or above current rates would
cause further warming and induce many changes in the global climate system during the 21st century that
would very likely23 be larger than those observed during the 20th century."  This section describes future
GHG emission scenarios, the associated changes in atmospheric concentrations and radiative forcing, and
the resultant changes in temperature, precipitation and sea level at global  and U.S. scales. Scenarios are
story lines regarding possible  futures.  These storylines are designed to be internally consistent in their
assumptions regarding population and economic growth, implementation  of policies, technology change
and adoption, and other factors that will influence  emissions. Scenarios are not projections of the future,
but are  used to illustrate how the future might  look if a given set of events occurred and policies
implemented. All future GHG emission scenarios described in this section assume no new explicit GHG
mitigation policies  ~   neither in the U.S. nor in other countries ~ beyond those which were already
enacted  at the time the scenarios were developed. Future risks and impacts associated with the climate
change projections are addressed in Part IV for domestic impacts and Part V for international impacts.

6(a)     Global emission scenarios and associated changes in concentrations and radiative forcing

Greenhouse Gas Emissions

As described in Section 4(a),  a number of different GHGs and other factors, including  aerosols, cause
radiative forcing changes and thus contribute to climate  change. This section discusses the  range of
published global reference (or  baseline) future emission projections for which no explicit GHG mitigation
policies  beyond those currently enacted are assumed.

The  IPCC's most recent future climate change projections from the Fourth Assessment Report (2007)
(discussed in Section 6(b) below) are based on the GHG emission scenarios from the IPCC Special
Report on Emission Scenarios (IPCC, 2000).  Box 6.1 provides background information on the  different
SRES emission scenarios.  The SRES developed a  range  of long-term  (out to the year 2100) global
reference scenarios for the major GHGs directly emitted by human activities and for some aerosols.  The
IPCC SRES scenarios do not  explicitly account for implementation of the Kyoto Protocol.  Figure 6.1
presents the global IPCC  SRES  projections for  the two  most significant anthropogenic GHGs: CO2
emissions primarily from the burning of fossil fuels, and CHt emissions.

Figure 6.1  Observed, and Projected Global CO2 and CH4 Emissions for the IPCC SRES Scenarios
            History        A18         A1FI          All          Kt           •           it'
   _ 30 j FossiI CO, Emissions
       1900   1950  2000  2050  21002000 2050  21002000 2050  21002000  2050  21002000 2050 21002000 2050   2100
23 According to IPCC terminology, "very likely" conveys a 90 to 99% probability of occurrence.  See Box 1.3 on
page 5 for a full description of IPCC's uncertainty terms.
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Source: Meehl et al. (2007).  Projected fossil CO2 and CH4 emissions for six illustrative SRES non-mitigation
Box 6.1:  IPCC Reference Case Emission Scenarios from the Special Report on Emission Scenarios

Al. The Al storyline and scenario family describes a future world of very rapid economic growth, global population that
peaks in mid-century and declines thereafter, and the rapid  introduction of new  and more efficient  technologies. Major
underlying  themes are convergence among regions, capacity building and increased cultural and social interactions, with a
substantial  reduction in regional differences in per capita income. The Al scenario family  develops into three groups that
describe alternative directions of technological change in the energy system. The three Al groups are distinguished by their
technological emphasis: fossil intensive (A1FI), non fossil energy sources (AIT), or a balance across all sources (A1B) (where
balanced is defined as not relying too heavily on one particular energy source, on the assumption that similar improvement
rates apply  to all energy supply and end use technologies).

A2. The A2 storyline and scenario family describes a  very heterogeneous world. The underlying theme is self reliance and
preservation of local identities. Fertility patterns across regions  converge very slowly, which results in continuously increasing
population. Economic development is primarily regionally oriented and per capita economic growth and technological change
more fragmented and slower than other storylines.

Bl. The Bl storyline and scenario family describes a convergent world with the same global population, that peaks in mid-
century and declines thereafter, as in the A 1 storyline, but with rapid change  in economic  structures toward a service and
information economy, with reductions in material intensity  and the introduction of clean and resource efficient technologies.
The emphasis  is on global solutions to economic, social and  environmental sustainability,  including improved equity, but
without additional climate initiatives.

B2. The B2 storyline and scenario family describes a world in which the emphasis  is on local solutions to economic, social
and environmental sustainability. It is a world with continuously increasing  global population, at a  rate lower than A2,
intermediate levels of economic development, and less rapid and more diverse technological change than in the Bl and Al
storylines. While the scenario is also oriented towards environmental protection and social equity, it focuses on local and
regional levels.

An illustrative scenario was  chosen for each of the six scenario groups A1B, A1FI, AIT,  A2, Bl and B2. All should be
considered  equally sound.

The SRES  scenarios do not include additional climate  initiatives, which means that no  scenarios are included that explicitly
assume implementation of the United Nations Framework Convention on Climate Change  or the emissions targets of the
Kyoto Protocol.
Box 6.2:  CCSP (2007b) Reference Case Emission Scenarios from Synthesis and Assessment Product 2.1

The scenarios in  this report were  developed using three integrated assessment models (lAMs). These  models integrate
socioeconomic and technological determinants of the emissions of GHGs with models of the natural science of Earth system
response, including the atmosphere, oceans, and terrestrial biosphere. The three lAMs used are:

         •    The Integrated Global Systems Model (IGSM) of the Massachusetts Institute of Technology's Joint Program on
             the Science and Policy of Global Change.
         •    The Model for Evaluating the Regional and Global Effects (MERGE) of GHG reduction policies developed
             jointly at Stanford University and the Electric Power Research Institute.
         •    The MiniCAM Model of the  Joint Global Change Research Institute, a partnership between the  Pacific
             Northwest National Laboratory and the University of Maryland.  The MiniCAM model was also used to
             generate IPCC SRES scenarios.

Each modeling group produced a reference scenario under the assumption that no climate policies are imposed beyond current
commitments, namely the 2008-12 first period of the Kyoto Protocol and the U.S. goal of reducing GHG emissions per unit of
its gross domestic product by 18% by 2012. The resulting reference cases are not predictions or best-judgment forecasts but
scenarios designed to provide clearly defined points of departure for  studying  the implications of alternative stabilization
goals. The modeling teams used model input assumptions  they considered meaningful and plausible. The resulting scenarios
provide insights into how the world  might evolve without additional efforts to constrain  GHG emissions,  given various
assumptions about principal drivers  of these emissions  such as population increase, economic growth, land and labor
productivity growth, technological options, and resource endowments.
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The main drivers of emissions are population, economic growth, technological change, and land-use
activities including  deforestation.  The detailed underlying assumptions (including final and  primary
energy by major fuel types)  across all  scenarios, and  across all modeling teams that produced the
scenarios, can be found in IPCC (2000). The range of GHG emissions in the scenarios widen over time to
reflect uncertainties in the underlying drivers. Similar future GHG emissions can result from different
socio-economic developments.  The IPCC (2000) SRES report did not assign probabilities or likelihood
to the scenarios, as it was stated that there is no single most likely, central, or best-guess scenario, either
with respect to  SRES scenarios or to the underlying scenario literature.  This is why IPCC (2000) has
recommended using  a range of SRES scenarios with a variety of underlying  assumptions  for use in
analysis.

Despite the range in future emission scenarios, the majority of all reference-case scenarios  project an
increase of GHG emissions across the century, and show that CO2 remains the dominant GHG over the
course of the 21st century. Total cumulative (1990 to 2100)  CO2 emissions  across the SRES scenarios
range from 2,826 gigatonnes of CO2
GtC).24
     (GtCO2) (or 770 GtC) to approximately 9,322  GtCO2 (or 2,540
Since the  IPCC SRES  (2000),
new scenarios in the literature
have emerged.  The emission
scenario range from the recent
literature is similar to the range
from  the  IPCC  SRES.   The
IPCC  (2007c)  reported  that
baseline    annual    emission
scenarios    published   since
SRES are  comparable in range
to those presented in the SRES
scenarios (25 to 135 GtCO2eq.
per year  in 2100).    Studies
since  SRES used lower values
for  some drivers for emissions,
notably population projections.
However,   for  those  studies
incorporating   these    new
population       projections,
changes in other drivers, such
as economic growth, resulted
in  little  change  in  overall
emission levels (IPCC, 2007c).
| Figure 6.2:  Projected Global Emissions of CO2 from Fossil Fuels
 and Industrial Sources across CCSP Reference Scenarios
                2020
                          2040
                 IGSM REF
                                    2060
                                MERGE REF
                                              2080
                                                        2100
                                                MINICAM REF
 Source: CCSP (2007b). Global emissions of CC>2 from fossil fuel combustion
 and other industrial sources, mainly cement production, increase over the
 century in all three reference scenarios.  By 2100 emissions reach 22.5 GtC/yr
 24.0 GtC/yr.
For comparison, Figure 6.2 provides global projections of CO2 emissions from the burning of fossil fuels
and industrial sources from the three reference-case  scenarios  developed by the U.S. Climate Change
Science Program  (CCSP,  2007b). Box  6.2 provides background  information on the  reference case
scenarios developed by the CCSP. The CCSP scenarios, because they were developed more recently than
the IPCC  SRES scenarios, do  account for the implementation of the Kyoto Protocol for participating
countries, but no explicit GHG mitigation policies beyond the Kyoto Protocol.  The emissions in 2100 are
approximately 88 GtCO2 (24 GtC).  This level of emissions is above the post-SRES IPCC median of 60
GtCO2 (16 GtC), but well within the 90th percentile of the IPCC range.
  1 Gigatonne (Gt) = 1 billion metric tons.
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Figure 6.3 illustrates reference case emission projections for CO2, CH/t, N2O, and the fluorinated gases in
aggregate (HFCs, PFCs, and SF6 or "F-gases"). The emissions projections in Figure 6.3 are from the 21st
Study of Stanford University's Energy Modeling Forum on multigas mitigation as referenced by Fisher et
al. (2007).  Eighteen models participated in the EMF-21 study and the emissions ranges in Figure 6.3  are
representative of the  literature. The  broad ranges of EMF-21 emissions projections  in Figure  6.3,
especially for N2O and the F-gases, illustrate the uncertainties in projecting these future emissions, which
is generally consistent with the range found in SRES.

Modeling groups have developed a multiplicity of projections for the concentrations of aerosol species.
Within the IPCC process, all the SRES scenarios specified sulfate emissions.  The inclusion, magnitude
and temporal evolution of other forcing agents such as nitrates and carbonaceous aerosols were left to the
discretion of the individual modeling groups. There are still large uncertainties associated with current
inventories of BC and OC, the ad hoc scaling methods used to produce future emissions, and considerable
variation among estimates of the optical properties of carbonaceous aerosols. Given these uncertainties,
future projections of forcing by BC and OC are quite dependent on the model and emissions assumptions
(Meehl et al., 2009). Similarly, CCSP (2008d) concluded that one of the most important uncertainties in
characterizing the potential climate impact of aerosols is the projection of their future emissions.
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Figure 6.3:  EMF-21 and IPCC Global Emissions Projections for CO2, CH4, N2O, and the
Fluorinated Gases
                                                           Grey area indicates
                                                           EMF21 range
         2000   2020    2040   2060
                                   2080   2100
                                                       2000    2020   2040   2060    2080
                                                                                        2100
     50
     40
     20
   £ 10
   LU
           CH4
                                                      50
                                    Grey area indicates
                                    EMF21 range
        2000    2020    2040   2060    2080   2100
                                                       2000    2020    2040   2060
                                                                                  2080    2100
                                                      12


                                                    I"
                                                    O  8

                                                    |  6


                                                    I  2
                                    Grey area indicates
                                    EMF21 range
        2000    2020   2040    2060    2080   2100
                                                       2000   2020    2040    2060   2080    2100
  6

I5
o 4

I 3


£ 1
          F-gases
                                     Grey area indicates
                                     EMF21 range
       2000    2020    2040    2060    2080    2100
                                                       2000    2020
                                                                     2040
                                                                           2060    2080
                                                                                         2100
         -AIM
          EDGE
         -GEMINI-E3
          IMAGE
          MESSAGE
          POLES
-AMIGA
-EPPA
-GRAPE
 IPAC
 MiniCAM
-SGM
                                     COMBAT
                                    -FUND
                                    -GTEM
                                     MERGE
                                     PACE
                                     W1AGEM
Source: CCSP (2007b). Development of baseline emissions in EMF-21 scenarios developed by  a
number of different modeling teams (left) and a comparison between EMF-21 and SRES scenarios (right).
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                            Figure 6.4  Projected Global CH4 and N2O Emissions across three
                            CCSP Reference Scenarios
                                     CH4 Emissions
                                   2020  2040   2060   2080  2100   2000  2020  2040   2060   2080   2100
                                         ' IGSM REF
                                                          MERGE REF
                                                                            MINICAM REF
For comparison, Figure 6.4
provides the  global  CFi4
and N2O projections  from
the  three   U.S.  CCSP
reference-case    scenarios
(CCSP, 2007b).

Future Concentration  and
Radiative Forcing
Changes

Figure 6.5 shows the  latest
IPCC  projected  increases
in atmospheric  CO2,  CFi4
and N2O concentrations for
the SRES  scenarios, and
Figure  6.6   shows   the
associated radiative forcing
for these CO2 scenarios. In
general,          reference
concentrations of CO2 and
other  GHGs  are projected to increase.   Concentrations of long-lived gases increase  even for those
scenarios where annual emissions toward the end of the century are assumed to be lower than current
annual emissions.  The CCSP scenarios show a similar picture of how atmospheric concentrations of the
main GHGs and total radiative forcing change over time.

Carbon dioxide is projected to be the largest contributor to total radiative forcing in all periods and the
radiative forcing associated with CO2  is projected to be the fastest growing. The  radiative forcing
associated with the non-CO2 GHGs is still significant and growing over time.
                            Source: CCSP (2007b).  Global anthropogenic emissions of CH4 and N2O vary
                            widely among the reference scenarios. There is uncertainty in year 2000 ChU
                            emissions, with MIT's IGSM reference scenario ascribing more of the emissions to
                            human activity and less to natural sources. Differences in scenarios reflect, to a
                            large extent, different assumptions about whether current emissions rates will be
                            reduced significantly for other reasons, for example, whether higher natural gas
                            prices will stimulate capture of CH4for use as a fuel.	
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Figure 6.5  Projected Global CO2, CH4 and N2O
Concentrations for the IPCC SRES Scenarios
   1200
   1000
 g- 800
 | 600

 I
 § 400
 o
   200
     0
      2006

   4000
2026
2046
2066
2086
   3500
 _a
 £ 3000
 o

 I 2500

 I
 8 2000
 ^r
 O
   1500
   1000
       2006
 2026
2046
2066
2086
   500
 g
 ra

 §  400

 8
o
CM
   350
   300
      2006
2026
 2046
2066
2086
        — A1B --A1T
         Scenarios
        , ..A1FI  —A2  —B1  	B2
Source: Meehl et al. (2007). Projected fossil CO2, CH4, and
N2O concentrations for six illustrative SRES non-mitigation
emission scenarios as produced by a simple climate model
tuned to 19 atmosphere-ocean general circulations models
(AOGCMs).

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Figure 6.6  Projected Radiative Forcing from CO2 for the IPCC SRES Scenarios
       History
                   A1B
      Radiative Forcing
   1900   1950   201
                   2050  21002000  2050 21002000  2050  21002000 2050  21002000 2050  21002000 2050  2100
Source: Meehl et al. (2007). Projected radiative forcing from CO2 for six illustrative SRES non-
mitigation emission scenarios as produced by a simple climate model tuned to 19 AOGCMs.  The
lighter shaded areas depict the change in this uncertainty range, if carbon cycle feedbacks are
assumed to be lower or higher than in the medium setting.	
6(b)   Projected changes in global temperature, precipitation patterns, sea level rise, and ocean
acidification

Using the emissions scenarios  described in Section 6(a), computer models project future changes in
temperature, precipitation and sea level at global and regional scales.  According to the IPCC (Meehl at
al., 2007):

"[Confidence in models comes from their physical basis, and their skill in representing observed climate
and past climate changes. Models have proven  to be extremely important tools for simulating  and
understanding climate, and there  is  considerable confidence  that they  are  able to  provide credible
quantitative  estimates of future climate change, particularly at larger scales. Models continue to have
significant limitations, such as in their representation of clouds, which lead  to uncertainties in the
magnitude and timing, as well as regional details, of predicted climate change. Nevertheless, over several
decades of model development, they have  consistently provided a robust and unambiguous picture of
significant climate warming in response to increasing greenhouse gases."25

Confidence decreases in changes projected by global models at smaller spatial scales.   Many important
small-scale processes cannot be represented explicitly in models, and so must be included in approximate
form as they interact with larger-scale features (Randall  et al., 2007).  Some of the most challenging
aspects  of understanding  and projecting regional climate changes relate to possible changes in the
circulation of the  atmosphere  and oceans,  and their patterns of variability  (Christensen  et al., 2007).
Nonetheless, the IPCC (2007d) concluded that recent advances in regional-scale modeling lead to higher
confidence in projected patterns of warming and other regional-scale features, including changes in wind
patterns, precipitation and some aspects of extremes and of ice.

The CCSP (2008c) report "Climate  Models: An  Assessment of Strengths  and Limitations" finds  that
models "have been steadily improving over the past several decades", "show many consistent features in
their simulations  and projections  for the future",  and "are able to simulate the recorded  20th Century
global mean temperature in a plausible way."  However,  it cautions that  projections of precipitation in
25 A number of climate models are developed and run at academic institutions and government supported research
laboratories in the U.S. and other countries.  The IPCC helps coordinate modeling efforts to facilitate comparisons
across models, and synthesizes results published by several modeling teams.
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some cases remain "problematic" (especially at the regional scale) and that "uncertainties in the climatic
effects of manmade aerosols (liquid and solid particles suspended in the atmosphere) constitute a major
stumbling block" in certain modeling experiments. It adds "uncertainties  related to clouds increase the
difficulty in simulating the climatic effects of aerosols, since these aerosols are known to interact with
clouds and potentially can change cloud radiative properties and cloud cover."

Global Temperature

The latest IPCC assessment uses a larger number of simulations available from a broader range of models
to project future climate relative to earlier assessments (IPCC, 2007d).  All of the simulations performed
by the IPCC project warming, for the full range of emissions scenarios.

For the next two decades, a warming of about 0.2°C (0.36°F) per decade is projected for a range of SRES
emission scenarios (IPCC, 2007d).  Even if the concentrations of all greenhouse gases and aerosols had
been kept constant at year 2000 levels (see the "Year 2000 Constant Concentrations" scenario in Figure
6.8), a further warming of about 0.1°C (0.18°F) per decade would be expected because of the time it takes
for the climate system, particularly the oceans, to reach equilibrium  (with year 2000  greenhouse gas
levels). Through about 2030, the warming rate is mostly insensitive to choices between the A2, A1B, or
Bl scenarios, and is consistent with that observed for the past few decades. Possible future variations in
natural forcings (e.g., a large volcanic eruption) could change these values somewhat (Meehl et al., 2007).
Large changes in emissions  of short-lived gases could also  have a near-term effect on temperatures,
especially on the regional scale (CCSP, 2008d).

According to IPCC (see Figure 6.8), by mid-century (2046-2065), the choice of scenario becomes more
important for the magnitude of the projected warming, with average  values of  1.3°C (2.3°F),  1.8°C
(3.2°F) and  1.7°C (3.1°F) from the models for scenarios  Bl (low emissions growth), A1B (medium
emissions growth) and A2 (high emissions growth), respectively (Meehl et al., 2007).  About a third of
that warming is projected to be due to climate change that is already committed (as shown in the "Year
2000 Constant Concentrations" scenario). By the 2090-2099 period (relative  to the 1980-1999 range),
projected warming varies significantly by emissions scenario.  The full suite of SRES scenarios  (given
below) provides a warming range of 1.8°C to 4.0°C (3.2°F to 7.2°F) with an uncertainty range of 1.1°C
to 6.4°C (2.0°F to 11.5°F). The multi-model average warming and associated uncertainty ranges  for the
2090-2099 period (relative to 1980-1999) for each scenario, as illustrated in Figure 6.8 are:

Scenario           Average Global Warming by End of       Uncertainty Range
                   Century Relative to -1990
Bl                  1.8°C(3.2°F)                              l.rCto2.90C(2.0°Fto5.2°F)
AIT               2.4°C(4.3°F)                              1.4°C to 3.8°C (2.5°F to 5.7°F)
B2                2.4°C (4.3°F)                              1.4°C to 3.8°C (2.5°F to 5.7°F)
A1B               2.8°C(5.0°F)                              1.7°C to 4.4°C (3.1°F to 7.9°F)
A2                3.4°C (6.1°F)                              2.0°C to 5.4°C (3.6°F to 9.7°F)
A1FI              +4.0°C (+7.2°F)                           2.4°C to 6.4°C (4.3°F to  11.5°F)

The  wide range  of  uncertainty in these estimates  reflects  the  different assumptions  about future
concentrations of greenhouse gases  and aerosols in the various scenarios considered by the IPCC and the
differing  climate sensitivities of the various climate models used in the simulations (NRC, 200 la; Meehl
et al., 2007).
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Figure 6.8 Multi-Model Averages and Assessed Ranges for Surface Warming
O
    6.0  -


    5.0  -
    4.0  -
A2
A1B
B1
Year 2000 Constant
Concentrations
20th century
                                               ©IPCC 2007:WG1-AR4
         1900
            2000
             Year
2100
Source: IPCC (2007d). Solid lines are multi-model global averages of surface warming (relative to 1980-
1999) for the scenarios A2, A1B and B1, shown as continuations of the 20th century simulations. Shading
denotes the ±1 standard deviation range of individual model annual averages. The orange line is for the
experiment where concentrations were held constant at year 2000 values. The grey bars at right indicate the
best estimate (solid line within each bar) and the likely range assessed for the six SRES marker scenarios.
The assessment of the best estimate and likely ranges in the grey bars includes the AOGCMs in the left part
of the figure, as well as results from a hierarchy of independent models and observational constraints.
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  Box 6.3: Climate Sensitivity
  The sensitivity of the climate system to a forcing is commonly expressed in terms of the global mean temperature
  change  that would be expected after a time sufficiently long for both the atmosphere  and ocean to  come to
  equilibrium with the change in climate forcing  (NRC, 2001).   Since IPCC's Third Assessment Report (IPCC,
  200 Ib), the levels of scientific understanding and confidence in quantitative estimates  of equilibrium climate
  sensitivity have increased substantially (Meehl et al. 2007).

  Solomon et al. (2007) indicate there is increased confidence of key  processes that are important  to climate
  sensitivity due to improved comparisons of models to one another and to observations.   Water vapor changes
  dominate the feedbacks  affecting climate sensitivity  and are now better understood.  Observational  and model
  evidence support a combined water vapor-lapse  rate (the rate at which air temperature decreases with altitude)
  feedback that corresponds to about a 50% amplification of global mean warming.  Cloud feedbacks  remain the
  largest source of uncertainty.

  Basing their assessment  on a combination of several independent lines of evidence, including  observed climate
  change and  the strength  of known feedbacks simulated in general circulation models, the  authors concluded that
  the global  mean equilibrium warming  for doubling  CO2 (a  concentration  of approximately 540 ppm),  or
  'equilibrium climate sensitivity', very likely greater than 1.5°C (2.7°F) and likely to lie in  the range 2°C to 4.5°C
  (3.6°F to 8.1°F), with a most likely value of about 3°C (5.4°F).  For fundamental physical reasons, as well as data
  limitations, the IPCC states a climate sensitivity higher than 4.5°C cannot be ruled out, but that agreement for these
  values with  observations and proxy data is generally worse compared to values in the 2-4.5°C range (Meehl et al.,
  2007).

  IPCC Climate Sensitivity Probabilities

  Less than 1.5°C                                      10% or less probability
  Less than 2.0°C                                      5-17% probability
  2°C to 4.5°C                                        66-90% probability
  Greater than 4.5°C                                   5-17% probability
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Geographical patterns of projected warming show greatest temperature increases over land (roughly twice
the global average temperature increase) and at high northern latitudes, and  less warming  over the
southern oceans and North Atlantic, consistent with observations (see Section 4b) during the latter part of
the 20th century (Meehl et al., 2007).

Global Precipitation

Models simulate  that global mean precipitation increases  with global warming  (Meehl et al., 2007).
However, there are substantial spatial and seasonal variations. Increases in the amount of precipitation are
very likely in high latitudes, while  decreases are likely in most subtropical land  regions, continuing
observed patterns in recent trends in observations. According to Solomon et al. (2007):

    •  In the northern hemisphere, a robust pattern of increased subpolar and  decreased  subtropical
       precipitation dominates the projected precipitation pattern  for the 21st century  over North
       America and Europe, while subtropical drying is less evident over Asia.
    •  In the southern hemisphere, there are few land areas in the zone of projected supolar moistening
       during the 21st century, with the subtropical drying more prominent.
    •  Projections of the precipitation over tropical land regions are more uncertain than those  at higher
       latitudes.

Global Sea Level Rise

By the end of the century (2090-2099), sea level is projected by IPCC (2007d) to  rise between  0.18 and
0.59 meters relative  to  the base period (1980-1999). These numbers represent the lowest  and highest
projections of the 5  to 95% ranges for all SPvES  scenarios considered collectively and include neither
uncertainty in carbon cycle feedbacks nor rapid dynamical changes in ice sheet flow.  In all scenarios, the
average rate of sea level rise during the 21st century very likely exceeds the 1961 to  2003 average rate (1.8
±0.5 mm per year).  Even if greenhouse  gas concentrations were to be stabilized, sea  level rise would
continue for centuries due to the time scales associated  with climate processes and feedbacks (IPCC,
2007d). Thermal expansion of ocean water contributes 70 to 75% of the central estimate for the rise in
sea level for all scenarios (Meehl et al., 2007).  Glaciers, ice caps and the Greenland Ice Sheet are also
projected to add to sea level.  The IPCC projects a range of sea level rise contributions from all glaciers,
ice caps,  and ice sheets between 0.04 meters to 0.23  meters, not  including the possibility  of rapid
dynamical changes. The Antarctic ice sheet is estimated to be a negative contributor to sea level  rise over
the next century under these assumptions (Meehl et al., 2007).

General Circulation Models indicate that the Antarctic Ice Sheet will receive increased snowfall without
experiencing substantial surface melting, thus gaining mass and reducing sea level rise according to IPCC
(Meehl et al., 2007). However, Meehl et al. (2007) note further accelerations  in ice flow of the kind
recently observed in some Greenland outlet glaciers and West Antarctic ice  streams could substantially
increase the contribution from the ice sheets, a possibility  not  reflected in the projections  above.  For
example, if ice discharge from these processes were to increase in proportion to global average surface
temperature change,  it would add  0.1 to 0.2 m to the upper bound of sea level rise by 2090  to 2099.
Dynamical processes related to  ice flow not included in current  models but suggested by  recent
observations could increase the vulnerability of the ice sheets to warming, increasing future sea level rise.

In the CCSP (2008a) report on abrupt climate change, Clark et al. (2008) find, "Recent  rapid changes at
the edges of the Greenland and West Antarctic ice sheets show acceleration of flow and thinning, with the
velocity of some  glaciers  increasing more than twofold."  They add, "Inclusion  of these processes in
models will likely lead to sea-level projections for the end of the 21st century that substantially exceed the
projections presented in the IPCC AR4 report."
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The  CCSP (2009b) sea level rise report notes, "It has been suggested by Rahmstorf (2007) and other
climate scientists that a global sea-level rise of 1 m (3  ft)  is plausible within this century if increased
melting of ice sheets in Greenland and Antarctica is added to the factors included in the IPCC estimates.
Therefore, thoughtful precaution suggests that  a global sea-level rise of 1m to the year 2100 should be
considered for future planning and policy discussions."

The  CCSP (2008c) report on the strengths and limitations of models notes that models of glacial ice are
"in their infancy" and that "recent evidence for rapid variations in this glacial outflow indicates that more-
realistic glacial models are needed to estimate the evolution of future sea level."

Sea level rise during the 21st century is projected by IPCC to have substantial geographic variability due
to factors that influence changes at the regional scale,  including changes in  ocean circulation or
atmospheric pressure, and geologic processes (Meehl et al.,  2007).  The patterns in different models are
not generally similar in detail, but have some common features, including smaller than average sea level
rise  in the Southern Ocean, larger than average sea level rise  in  the Arctic,  and a narrow  band of
pronounced sea level rise stretching across the southern Atlantic and Indian Oceans.

Global Ocean Acidification

The oceans have absorbed, and will continue to absorb, carbon dioxide emissions associated with
anthropogenic activities.  Surface ocean pH has decreased by 0.1 units due to oceanic absorption of CO2,
and it is predicted to decrease by an additional 0.3-0.4 units by 2100 (Fischlin et al.,  2007). This
projected rate of decline may lead to ocean pH levels within a few centuries that have not been observed
for a few hundred million years (Denman et al., 2007).  Acidification is affecting calcium carbonate
saturation in ocean waters, and is thereby reducing calcification rates of organisms who rely on the
minerals for development. Future acidification is projected to result in under-saturated ocean waters (see
Box  14.1 for information on the effects of this undersaturation). Polar and sub-polar surface waters and
the Southern Ocean will be aragonite (a form of calcium carbonate) under-saturated by 2100, and Arctic
waters will be similarly threatened (Fischlin et al., 2007).  According to a model experiment using a
'business as usual' emission scenario (IPCC -IS92a), bio-calcification will be reduced by 2100, in
particular within the Southern Ocean, and by 2050 for aragonite-producing organisms (Denman et al.,
2007).

6(c)     Projected changes in U.S. temperature, precipitation patterns, and sea level rise

IPCC's Fourth Assessment Report includes projections for changes in temperature, precipitation and sea
level rise  for North America ~ which  can be  generalized for the U.S - as well as some U.S. specific
information. These projections are summarized in this section.

U.S.  Temperatures

According to the IPCC,  all  of North America is very likely to warm during this century as shown in
Figures in 6.9 and 6.10, and  warm more than the global mean warming in most areas (Christensen et al.,
2007). For scenario A1B (moderate emissions growth), the largest warming through 2100 is projected to
occur in winter over northern parts of Alaska, reaching 7-10°C (13-18°F) in the northernmost parts as
shown in  Figure 6.10, due to the positive feedback from a shorter season of snow cover.  In  western,
central and eastern regions of North America, the projected warming has less seasonal variation and is not
as large, especially near the coast, consistent with less warming over the oceans. The average warming in
the U.S. through 2100 is projected by nearly all the models  used in the IPCC assessment to exceed 2°C
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(3.6°F) for all scenarios (see Figure 6.9), with 5 out of 21 models projecting average warming in excess of
4°C (7.2°F) for the A1B (mid-range) emissions scenario.

The CCSP (2008e)  report "The Effects of Climate Change  on Agriculture, Land Resources, Water
Resources,  and Biodiversity" provides  shorter-term temperature projections for the U.S.  for the year
2030.  It projects a warming of approximately 1°C in the southeastern U.S., to more than 2°C in Alaska
and northern Canada, with other parts of North America having intermediate values (Backlund  et al.,
2008b).
Figure 6.9: Temperature anomalies with respect to 1901 to 1950 for four North American
land regions
                  Alaska
Western North America
°C 4
   1900    1950    2000     2050    2100    1900    1950    2000     2050    2100
           Central North America
 Eastern North America
°C 4
   1900    1950    2000     2050    2100    1900
 1950    2000
2050    2100
Source: Christensen et al. (2007). Temperature anomalies with respect to 1901 to 1950 for
four North American land regions for 1906 to 2005 (black line) and as simulated (red envelope)
by multi-model dataset (MMD) models incorporating known forcings; and as projected for 2001
to 2100 by MMD models for the A1B scenario (orange envelope). The bars at the end of the
orange envelope represent the range of projected changes for 2091 to 2100 for the B1
scenario (blue), the A1B scenario (orange) and the A2 scenario (red). The black line is dashed
where observations are present for less than 50% of the area in the decade concerned.
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     Figure 6.10: Projected temperature and precipitation changes over North America from
     the MMD-A1B simulations.
                  Annual
December/January/February     June/July/August
     30"N
     1ITN
        180°   140°W   100°W   60°W   20°W180°   140°W  100°W   60°W   20°W180°   140°W   100°W   60°W   20°W
                                    10 7  5 « 35 325 ! 11 1 OS 0 -09-1
                                       Temperature Response (°C)
     70«N
     50-N
     30°N
     10»N
        180°
             140°W   100°W   60°W   20°W180°   14O°W  100°W   60°W   20°W180°   140°W   100"W   60°W
                                    50 30 20 15 10 5 0 -5-10-15-20-30-50
                                          Prec Response {%)

     Source: Christensen et al. (2007). Top row: Annual mean, December-January-February, and June-July-
     August temperature between 1980 to 1999 and 2080 to 2099, averaged over 21 models. Bottom row:
     same as top, but for fractional change in precipitation.
U.S. Precipitation

A widespread increase in annual precipitation is projected by IPCC over most of the North American
continent except the south and south-western part of the U.S. and over Mexico largely consistent with
trends in recent decades (as described in Section 4) (Christensen et al., 2007).  The largest increases are
projected over northern North America (i.e. Canada and Alaska) associated with a poleward shift in storm
tracks where precipitation increases by the largest amount in autumn and by the largest fraction in winter
as shown in Figure 6.10.  In western North America, modest changes in annual mean precipitation are
projected, but the majority of models indicate an increase in winter and a decrease in summer.   Models
show greater consensus on winter increases to the north and on summer decreases to the south. These
decreases are consistent with enhanced subsidence  and flow of drier air masses in the southwest U.S. and
northern Mexico.  Accordingly, some models project drying in the southwest U.S., with more than 90%
of the models projecting drying in northern and particularly western Mexico. On the windward slopes of
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the mountains in the west, precipitation increases are likely to be enhanced due to orographic lifting26. In
the northeastern U.S., annual mean precipitation is very likely to increase.

U.S.  Sea Level Rise

For North American coasts, emissions scenario A IB shows sea level rise values close to the global mean,
with slightly higher rates in eastern Canada and western Alaska, and stronger positive anomalies in the
Arctic.  The projected rate of sea level rise off the low-lying U.S. South Atlantic and Gulf coasts is also
higher than the global  average. Vertical land motion from geologic processes may decrease (uplift) or
increase (subsidence) the relative sea level rise at any site (Nicholls et al., 2007).

Impact of Short-lived Species on U.S. Temperature and Precipitation

Modeling results suggest that changes in short-lived species (mainly sulfates and black carbon) may
significantly influence  21st century climate.   A GFDL  simulation of SRES scenario A IB  shows that
changes in short lived  species could be responsible for up to 40% of the continental U.S. summertime
warming projected to occur in this scenario by 2100 along with  a statistically significant decrease in
precipitation, mainly due to a combination of domestic sulfate emissions reductions and increases in
Asian black carbon emissions (CCSP, 2008d).  However, the CCSP study concludes that "we could not
find  a consensus in this report on the duration, magnitude, or even sign (warming or cooling) of the
climate change due to future levels of the short-lived gases and  particles"  due to uncertainties about
different pollution control storylines.

6(d)     Cryosphere (Snow and Ice) projections, focusing on North America and the U.S.

Snow season length and snow depth are very likely to decrease in most of North America as illustrated in
Figure 6.11, except in the northernmost part of Canada where maximum snow depth is likely to increase
(Christensen et al., 2007). Widespread increases in thaw depth are projected over most permafrost regions
globally (IPCC, 2007d).

Lettenmaier et al. (2008) find where shifts to earlier snowmelt peaks and reduced summer and fall low
flows have already been detected, continuing shifts in this direction are very likely.

Meehl et al (2007) conclude that  as the climate warms,  glaciers will lose mass owing to dominance of
summer melting over winter precipitation increases,  contributing to sea level rise.
26 Orographic lifting is defined as the ascent of air from a lower elevation to a higher elevation as it moves over
rising terrain
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Sea  ice  is  projected  to
shrink  in  both the Arctic
and the Antarctic under all
SRES  scenarios.  In some
projections,   Arctic   late-
summer sea ice disappears
almost entirely by the latter
part  of the  21st  century
(IPCC, 2007d).    Taking
into  account  recent  late
summer   sea  ice   loss,
Polyak   et   al    (2009)
indicate that  the   Arctic
Ocean   may   become
seasonally  ice  free  as
early as 2040.
                            Figure 6.11 Percent Snow Depth Changes in March
DS

100
50
25
10
5
1
-1
-5
-10
-25
-50
-100
                            Source: Christensen et al. (2007).  Percent snow depth changes in March (only
                            calculated where climatological snow amounts exceed 5mm of water equivalent),
                            as projected by the Canadian Regional Climate Model (CCRM), driven by the
                            Canadian General Circulation Model (CGCM), for 2041 to 2070 under SRES A2
                            compared to 1961 to 1990.
6(e)    Extreme   events,
focusing    on     North
America and the U.S.

Models    suggest    that
human-induced    climate
change is expected to alter
the prevalence and severity
of many extreme  events
such as  heat  waves,  cold
waves, storms, floods, and
droughts.  This section describes CCSP (2008i) and IPCC's projections for extreme events focusing on
North America and the U.S. Sections 7-14 summarize some of the sectoral impacts of extreme events for
the U.S.

Temperature

According to  the IPCC,  it is very likely that heat waves globally will become more intense,  more
frequent, and longer lasting in a future warm climate, whereas cold episodes are projected to  decrease
significantly.  (Meehl, GA. et al., 2007).  Meehl et al., 2007 report on a study finding that the pattern of
future changes in heat waves, with greatest intensity increases over western Europe, the Mediterranean
and the southeast and western U.S., is related in part to circulation changes resulting from an increase in
greenhouse gases.

The IPCC cites a number of studies that project changes in temperature extremes in the U.S. (Christensen
et al., 2007).  One finds that the frequency and the magnitude of extreme temperature  events changes
dramatically under a high-end emission scenario (SRES A2), with increases  in extreme hot events and
decreases in  extreme cold events.     Another examines changes in temperature  extremes  in their
simulations centered on California and finds increases  in extreme temperature events, prolonged hot
spells and increased diurnal temperature range.  A third finds increases in diurnal temperature range  in six
sub-regions of the western U.S. in summer.
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Karl et al.  (2008) find for a mid-range scenario (A1B) of future GHG emissions, a day so hot that it is
currently experienced only once every 20  years would occur every three years by the middle of the
century over much of the continental U.S. and by the end of the century, it would occur every other year
or more.

Some implications for human health resulting from these projected changes in temperature extremes are
discussed in Section 7(b).

Precipitation and Storms

Intensity of precipitation events is projected to increase globally, particularly in tropical and high latitude
areas that experience  increases in mean precipitation (Meehl et al., 2007).  Even  in areas where mean
precipitation decreases (most subtropical and mid-latitude regions), precipitation intensity is projected to
increase  but there would be longer periods  between rainfall events.  Meehl  et al.  (2007)  note that
increases in heavy precipitation events have been linked to increases in flooding.

The IPCC projects a tendency for drying in mid-continental areas during summer, indicating a greater risk
of droughts in those regions (Meehl et al., 2007). Extreme drought increases from 1% of present-day land
area to 30% by the end  of the century in the A2 (high emissions growth) scenario according to a study
assessed in Meehl et al.  (2007). Karl et al. (2008) indicate that for a mid-range emission scenario (A1B),
daily precipitation  so heavy  that  it now  occurs  only once every  20 years is projected  to  occur
approximately every eight years by the end of this century over much of Eastern North America.

Future projections in Gutowski et al. (2008) indicate strong mid-latitude (or extratropical) storms will be
more frequent though the overall number of storms may decrease.

Several regional studies  in the IPCC project changes in precipitation extremes in parts of the U.S ranging
from a decrease in heavy precipitation in California to an increase during winter in the northern Rockies,
Cascades and Sierra Nevada mountain ranges (Christensen et al., 2007).  For the contiguous U.S., a study
in Christensen et al. (2007)  finds widespread  increases in extreme  precipitation events under SRES A2
(high emissions growth).

Based on a range of models, it is likely that tropical cyclones (tropical storms and hurricanes) will become
more intense, with stronger peak winds and more heavy precipitation associated with ongoing increases
of tropical sea surface temperatures (IPCC, 2007d).  Karl et al. (2008) analyze model simulations and find
that for each 1°C (1.8°F) increase in tropical sea surface temperatures, core rainfall  rates will increase by
6-18% and the surface wind speeds of the strongest hurricanes will  increase by about 1-8%. Storm surge
levels are likely to increase due to projected sea level rise, but note the degree of projected increase has
not been adequately studied.

Karl et al.  (2008)  indicate  projections in  frequency changes in  tropical  cyclones  are  currently too
uncertain for confident projections.  Some modeling  studies have projected a decrease in the number of
tropical cyclones globally due to increased stability of the tropical atmosphere in a warmer climate,
characterized by fewer  weak storms and greater numbers of intense storms (Meehl et al., 2000).  A
number of modeling studies have also projected a general tendency for more intense but fewer storms
outside the tropics, with  a tendency towards more extreme wind events and higher ocean waves in several
regions associated with these deepened cyclones (Meehl et al., 2007).

Possible implications of extreme precipitation events in the U.S. for health  are described in  Chapter 7, for
food production and  agriculture in Section 9, for water resources in Section 11, for coastal areas in
Section 12, and for ecosystems and wildlife in Section 14.
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6(f)    Abrupt Climate Change and High Impact Events

CCSP (2008a), in its report on abrupt climate change, defines it as a "large-scale change in the climate
system that takes place over a few decades or less, persists (or is anticipated to persist) for at least a few
decades,  and causes substantial disruptions in human and natural systems."  Abrupt climate changes are
an important consideration because, if triggered, they could occur  so  quickly and unexpectedly that
human or natural systems would have difficulty adapting to them (NRC, 2002). Potential abrupt climate
change implications in the U.S. are not  discussed in the sections 7 through 14 (the U.S. sectoral impacts)
because they cannot be predicted with confidence, particularly for specific regions. This section therefore
focuses on the general risks of abrupt climate change globally, with some discussion of potential regional
implications where information is available.

According to the National Research Council (2002): "Technically, an abrupt climate change occurs when
the climate system is forced to cross  some threshold, triggering a transition to a new  state at a rate
determined by the climate system itself and faster than the  cause." Crossing systemic thresholds may lead
to large and widespread consequences  (Schneider et al., 2007).   The triggers  for abrupt  climate change
can be forces that are external and/or internal to the climate system including (NRC, 2002):

•   changes in the Earth's orbit27
•   a brightening or dimming  of the sun
•   melting or surging ice sheets
•   strengthening or weakening of ocean currents
•   emissions of climate-altering gases and particles into the atmosphere

More than one of these triggers can operate simultaneously,  since all components of the  climate system
are linked.

Scientific data  show that abrupt changes in the climate at the  regional scale  have occurred throughout
history and are characteristic of the Earth's climate system (NRC, 2002).  During the last glacial period,
abrupt regional warmings  (8 to 16°C within decades over Greenland) and coolings occurred repeatedly
over the North Atlantic region (Jansen  et al., 2007). These warmings  likely had some large-scale effects
such as major shifts in tropical rainfall patterns and redistribution of heat within the climate system but it
is unlikely that they were associated with large changes in global mean surface temperature.

The National Research Council concluded that anthropogenic forcing may increase the risk of abrupt
climate change (NRC, 2002):

"...greenhouse warming and other human alterations of the Earth system may increase the possibility of
large, abrupt, and unwelcome regional  or global climatic  events. The abrupt changes  of the past are not
fully  explained yet,  and climate models typically underestimate the size, speed, and extent of those
changes.  Hence, future abrupt changes  cannot be predicted with confidence, and climate  surprises are to
be expected."

Changes  in weather patterns (sometimes referred to as weather regimes or natural modes)  can result from
abrupt changes that might occur spontaneously due to dynamical interactions in the atmosphere-ice-ocean
system, or from the crossing of a threshold from slow external forcing (as described above) (Meehl et al.,
27 According to the National Research Council (2002), changes in the Earth's orbit occur too slowly to be prime
movers of abrupt change but might determine the timing of events.  Abrupt climate changes of the past were
especially prominent when orbital processes were forcing the climate to change during the cooling into and warming
out of ice ages (NRC, 2002).
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2007). In a warming climate, changes in the frequency and amplitudes of these patterns might not only
evolve rapidly, but also trigger other processes that lead to abrupt climate change (NRC, 2002). Examples
of  these  patterns  include  the  El Nino  Southern Oscillation  (ENSO)28  and the  North  Atlantic
Oscillation/Arctic Oscillation (NAO/OA).29

ENSO has important linkages to patterns of tropical sea surface temperatures, which historically have
been strongly tied to drought, including "megadroughts" that likely occurred between 900-1600 A.D. over
large  regions of the southwestern U.S. and  Great Plains (Clark et al.,  2008).  The possibility  of severe
drought as an abrupt  change resulting from changes in sea surface temperatures in a warming world is
assessed by Clark et al. (2008). They find that under greenhouse warming scenarios, the cause of model-
projected sub-tropical drying is an overall widespread warming of the ocean and atmosphere, in contrast
to the causes of historic droughts (linked specifically to sea surface temperature). But they note models
may not correctly represent the ENSO patterns of tropical SST change that could create impacts on global
hydroclimate (e.g., drought) in addition to those caused by overall warming. The current model results do
show drying over the southwestern U.S., potentially increasing the likelihood of severe and persistent
drought there in the future.  Clark et al. (2008) note this drying has already begun (see also section 4k) but
caution it is not clear if the present drying is outside  the  range  of natural variability and  linked  to
anthropogenic causes.

Scientists have investigated the possibility of an abrupt slowdown or shutdown of the  Atlantic meridional
overturning circulation (MOC) triggered by greenhouse gas forcing.  The MOC transfers large quantities
of heat to the North Atlantic and Europe so  an abrupt  change  in  the MOC  could have important
implications for the climate of this region  (Meehl et al.,  2007).  However, according to  Meehl et al.
(2007), the probability of an abrupt change in (or shutdown of) the MOC is low: "It is very unlikely that
the  MOC  will undergo a large abrupt transition during the 21st century. Even further into the  future,
Clark et al. (2008) note "it  is unlikely that  the Atlantic MOC will collapse beyond  the end of the 21st
century because of global warming, although the possibility cannot be entirely excluded." While models
project a slowdown in the  MOC over the  21st  century and  beyond, it is so  gradual that  the resulting
decrease in heat transport to the North Atlantic and Europe would not be large enough to reverse the
warming that results from the increase in GHGs (Clark et al., 2008).  Clark et al. (2008) do caution that
while a collapse of the MOC is unlikely, the potential consequences of this  event could be severe if it
were to happen. Potential impacts include a southward shift  of the tropical rainfall belts, additional sea
level rise around the North Atlantic, and disruptions to marine ecosystems.

The rapid disintegration  of the  Greenland Ice  Sheet (GIS),  which would raise sea levels 7 meters,  is
another commonly discussed abrupt change. Clark et al. (2008) report that observations demonstrate that
it is extremely likely  that the Greenland Ice Sheet is losing mass and that this loss has very likely been
accelerating since the mid-1990s. In the CCSP (2009b) report "Past  Climate Variability and Change in the
Arctic and at High Latitudes", Alley et al. (2009)  find a threshold for ice-sheet removal from  sustained
summertime warming of 5°C, with a range of uncertainties  from 2° to 7°C. Meehl et al. (2007) in IPCC
  ENSO describes the full range of the Southern Oscillation (see-saw of atmospheric mass or pressure between the
Pacific and Indo-Australian areas) that includes both sea  surface temperature (SST) increases as well as SST
decreases when compared to a  long-term average. It has sometimes been used by scientists to  relate only  to the
broader view of El Nino or the warm events, the warming of SSTs in the central and eastern equatorial Pacific. The
acronym, ENSO, is composed of El Nino-Southern Oscillation, where El Nino is the oceanic component and the
Southern Oscillation is the atmospheric component of the phenomenon.
29 The North Atlantic Oscillation (NAO) is the dominant mode of winter climate variability in the North Atlantic
region ranging from central North America to Europe and much into Northern Asia. The NAO is a large scale
seesaw in atmospheric mass or pressure between the subtropical high and the polar low. Similarly, the Arctic
Oscillation (AO) refers to opposing atmospheric pressure patterns in northern middle and high latitudes.  The NAO
and AO are different ways of describing the same phenomenon.
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suggest the complete melting of the GIS would only require sustained warming in the range of 1.9°C to
4.6°C (relative to the pre-industrial temperatures) but suggest it would take many hundreds of years to
complete.

A collapse of the West Antarctic  Ice Sheet  (WAIS), which would raise seas 5-6 meters,  has been
discussed as a low probability, high impact response to global warming (NRC, 2002; Meehl et al.,  2007).
The weakening or collapse of ice shelves, caused by melting on the surface or by melting at the bottom by
a warmer ocean, might contribute  to a potential destabilization of the WAIS.  Recent satellite and  in situ
observations of ice streams behind disintegrating ice shelves highlight some rapid reactions of ice sheet
systems (Lemke et al., 2007).  Clark et al. (2008) indicate that while  ice is thickening over some  higher
elevation regions of Antarctica, substantial ice losses from West Antarctica and the Antarctic  Peninsula
are very likely occurring and that Antarctica is losing ice on the whole. Ice sheet  models are only
beginning to capture the small-scale dynamical processes that involve complicated interactions with the
glacier bed and the ocean at the perimeter of the  ice sheet (Meehl et al., 2007).  These processes are not
represented in the models used by IPCC to project sea level rise. These models suggest Antarctica will
gain mass due to increasing snowfall, (although recent studies find no significant continent-wide trends in
snow accumulation over the past several decades; Lemke et al., 2007), reducing sea level  rise.  But it is
possible that acceleration of ice discharge could become  dominant, causing a net positive contribution.
Given these competing factors, there is presently no consensus on the long-term future of the WAIS or its
contribution to sea level rise (Meehl et al., 2007).

Considering the Greenland  and  West Antarctic  ice  sheets together, Schneider  et al. (2007)  find
paleoclimatic evidence suggests that Greenland and possibly the WAIS contributed to a sea-level  rise of
4-6 meters during the last  interglacial, when polar temperatures were  3-5 degrees C  warmer, and the
global  mean was  not notably warmer,  than at present.  Accordingly,  they  conclude  with medium
confidence that at least partial deglaciation of the Greenland  ice sheet, and possibly the  WAIS,  would
occur over a period of time ranging from centuries to millennia for a global average temperature increase
of 1-4  degrees Celsius (relative to 1990-2000), causing a contribution to sea-level rise of 4-6  meters or
more.

Another potential abrupt change  of concern assessed by  CCSP (2008a) is the catastrophic release of
methane from clathrate hydrates in the sea floor and to a lesser extent in permafrost soils.  Clark et al.
(2008) find the following:

    •   The size of the hydrate reservoir is uncertain, perhaps by up to a factor of 10 making judgments
       about risk difficult to assess.

    •   Although there are  a number of suggestions in the literature  about the possibility of a dramatic
       abrupt release  of methane to the atmosphere, modeling and  isotopic fingerprinting of ice-core
       methane do not support such a release to the atmosphere over the last 100,000 years or in the near
       future.

Clark et al (2008) conclude:

    "While the risk of catastrophic release of methane to the atmosphere in the next century appears very
    unlikely, it  is very likely that climate change will accelerate the  pace of persistent emissions from
    both hydrate sources and wetlands. Current models suggest that wetland emissions could  double in
    the next century. However, since these models do not realistically  represent all the processes thought
    to  be  relevant to future northern  high-latitude QrU emissions, much larger (or smaller)  increases
    cannot be discounted. Acceleration of persistent release  from hydrate reservoirs  is  likely, but its
    magnitude is difficult to estimate."
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6(g)   Effects on/from Stratospheric Ozone

Substances that deplete stratospheric ozone, which protects the Earth's surface from much of the sun's
biologically harmful ultraviolet radiation, are regulated under Title VI of the Clean Air Act. According to
the World Meteorological Organization (2007), climate change that results from changing greenhouse gas
concentrations will affect the  evolution of the ozone layer  through changes in chemical  transport,
atmospheric composition, and  temperature.   In turn,  changes in the  stratospheric  ozone  can have
implications for the  weather and climate of the troposphere.   The coupled interactions between the
changing climate and ozone layer are complex and scientific understanding is incomplete (WMO, 2007).
Specific information on climate change effects  on/from stratospheric ozone  in the U.S. has not been
assessed.  Except where indicated, the findings in this section apply generally to the globe with a focus on
polar regions.

Effects of Elevated Greenhouse Gas Concentrations on Stratospheric Ozone

The  World Meteorological  Organization's  (WMO) 2006  Scientific Assessment of Ozone Depletion
(2007) concluded that future concentrations of stratospheric ozone are sensitive  to future levels of the
well-mixed greenhouse gases. According to the WMO (2007):

    •  Future increases of greenhouse gas concentrations, primarily CO2, will contribute to the average
       cooling in the stratosphere.  Stratospheric cooling is expected to slow gas-phase ozone depletion
       reactions and increase ozone.
    •  Enhanced  methane emission  (from warmer and wetter soils) is expected to enhance ozone
       production in the lower stratosphere.
    •  An increase  in nitrous  oxide emissions is  expected to  reduce ozone in the middle and  high
       stratosphere.

Two-dimensional models that include coupling between all of these well-mixed greenhouse gases and
temperature project that ozone levels between 60° S and 60° N will return to 1980 values up to 15 years
earlier than in models that are uncoupled (Bodeker et al., 2007).  The impact of stratospheric cooling on
ozone might be the opposite in  polar regions where cooling could cause increases in polar stratospheric
clouds, which, given enough halogens, would increase ozone loss (Bodeker et al., 2007).

Concentrations of stratospheric ozone are also sensitive to stratospheric water vapor concentrations which
may remain relatively constant or increase (Baldwin et al., 2007).  Increases in water vapor would cause
increases  in hydrogen oxide (HOX) radicals,  affecting ozone  loss processes (Baldwin  et  al.,  2007).
Several studies  cited in Baldwin et al. (2007) suggest increasing stratospheric water vapor would delay
ozone  layer recovery.  Increases in stratospheric water vapor could also increase spring-time ozone
depletion in the polar regions by raising the temperature threshold for the formation of polar stratospheric
clouds (WMO, 2007).

The possible effects of climate change on stratospheric ozone are further complicated by possible changes
in climate  dynamics.  Climate  change  can  affect temperatures, upper level winds  and storm patterns
which, in turn, impact planetary waves that affect the stratosphere (Baldwin et al., 2007).  Changes in the
forcing and propagation of planetary waves30 in the polar winter are a major source of uncertainty for
predicting future levels of Arctic ozone loss (Baldwin et al., 2007).
30 A planetary wave is a large horizontal atmospheric undulation that is associated with the polar-front jet stream and
separates cold, polar air from warm, tropical air.
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The CCSP (2008h) report "Trends in Emissions of Ozone-Depleting Substances, Ozone Layer Recovery,
and Implications for Ultraviolet Radiation Exposure" includes results from two-dimensional chemistry
transport models and three-dimensional climate chemistry models estimating the recovery of the ozone
layer under a greenhouse gas scenario.  It finds:

    •   From 60°N to 60°S, global ozone is expected to return to its 1980 value up to 15 years earlier
       than the halogen recovery date because of stratospheric cooling and changes in circulation
       associated with GHG emissions.  Global ozone abundances are expected to be 2 percent above
       the 1980 values by 2100 with values at mid-latitudes as much as 5 percent higher.

    •   Model simulations show that the ozone amount in the Antarctic will reach the 1980 values 10 to
       20 years earlier (i.e. from 2040 to 2060) than the 2060 to 2070 time frame of when the ozone-
       depleting substances reach their 1980 levels in polar regions.

    •   Most climate chemistry models show Arctic ozone values by 2050 larger than the 1980 values,
       with the recovery date between 2020 and 2040.

Climate Change Effects from Stratospheric Ozone

The WMO (2007) found changes to the temperature and circulation of the stratosphere affect climate and
weather in the troposphere.   The dominant tropospheric response, simulated in models and identified in
analyses  of observations,  comprises changes in the  strength of mid-latitude westerly winds.   The
mechanism for this response is not well-understood.

Modeling experiments (that simulate observed changes in stratospheric ozone and combined stratospheric
ozone depletion and GHG increases)  also suggest that Antarctic ozone depletion, through its effects on
the lower stratospheric vortex, has contributed to the observed surface cooling over interior Antarctica
and warming of the Antarctic Peninsula, particularly in summer (Baldwin et al., 2007). While the physics
of these effects are not well-understood, the simulated pattern of warming  and cooling is a robust result
seen in many different models, and well-supported by observational studies.

As the ozone layer recovers, tropospheric changes that have occurred as a result of ozone depletion are
expected to reverse (Baldwin et al., 2007).

6(h) Land-Use and Land Cover Change

Changes  in land surface (vegetation, soils, water) resulting from human activities can significantly affect
local climate through shifts in radiation, cloudiness, surface roughness, and surface temperature.

Solomon et al. (2007) find the impacts of land use change on climate are expected to be locally significant
in some regions, but are small at the global scale in comparison with greenhouse warming. Similarly, the
release of heat from anthropogenic energy production  can be  significant over urban areas, but is not
significant globally (Solomon et al., 2007).

The CCSP report (2008e) on the effects of climate change on agriculture, land resources, water resources,
and biodiversity in the U.S. concludes that global climate change effects  will be superimposed on and
modify those resulting from land use and land cover patterns in ways that are as of yet uncertain.
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                               Part IV

 U.S. Observed and Projected Human Health and Welfare Effects from
                          Climate Change
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Section 7

Human Health

Warm temperatures and extreme weather already cause and contribute to adverse human health outcomes
through heat-related mortality and morbidity, storm-related fatalities and injuries, and disease.  In the
absence of effective adaptation, these effects are likely to increase with climate change. Depending on
progress in health care and access, infrastructure, and technology, climate change could increase the  risk
of heat wave deaths, respiratory illness through exposure to aeroallergens and ozone (discussed in Section
8), and certain diseases (CCSP,  2008b; Confalonieri et al, 2007).  Studies in temperate areas (which
would include large portions of the U.S.) have shown that climate change is  projected to bring some
benefits, such as fewer deaths from cold exposure.  The balance of positive and negative health impacts as
a result of climate change will vary from one location to another, and  will alter over time as climate
change continues (CCSP, 2008b).

In its Third Assessment Report (TAR), the IPCC produced a number of key findings summarizing the
likely climate change health effects in North America.  These effects, which were reaffirmed in the IPCC
Fourth Assessment Report (Field  et al., 2007), include:

•   Increased deaths,  injuries, infectious diseases, and stress-related disorders and other adverse effects
    associated with social disruption and migration from more frequent extreme weather.
•   Increased frequency and severity of heat waves leading to more illness and death, particularly among
    the young, elderly and frail.
•   Expanded ranges of vector-borne and tick-borne diseases in  North America but with moderating
    influence by public health measures and other factors.

The more  recent CCSP (2008b) report on human health stated as one of its conclusions that, "The United
States is certainly capable of adapting to the collective impacts of climate change. However, there will
still be certain individuals and locations where the adaptive capacity is less and these individuals and their
communities will be disproportionally impacted by climate change."

There are few studies which address the interactive effects of multiple climate  change impacts or of
interactions between climate change health impacts and other kinds of local, regional, and global socio-
economic  changes (Field et al., 2007).  For example, climate change impacts on human health in urban
areas will  be compounded by aging infrastructure, maladapted urban form and building stock, urban heat
islands, air pollution, population growth and an aging population (Field et al., 2007).

Vulnerability is the  summation of all the factors of risk and resilience that determine whether individuals
experience adverse health  impacts. Specific subpopulations may experience heightened vulnerability for
climate-related health effects.  Climate change is very likely to accentuate the disparities already evident
in the  American health  care systems as many  of the expected  health effects  are  likely to  fall
disproportionately on the poor, the elderly, the disabled, and the uninsured (Ebi et al., 2008).

This section describes the literature on the impacts of climate change  on human health in four  areas:
temperature effects, extreme events, climate sensitive diseases,  and aeroallergens.  The health impacts
resulting from climate change effects on air quality are discussed in Section 8.

7(a)    Temperature Effects
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According to the IPCC (2007d), it is very likely31 that there were warmer and fewer cold days and nights
and warmer and more frequent hot days over most land areas during the late 20th century (see section
4(b)). It is virtually certain that these trends will continue during the 21st century (see Section 6(b)).  As a
result of the projected warming, the IPCC projects increases in  heat-related mortality and morbidity
globally (IPCC, 2007b).   The projected warming is expected to result in fewer deaths due to reduced
exposure to the cold.  It is not clear whether reduced mortality from  cold will be greater or less than
increased heat-related mortality in the U.S. due to climate change (Gamble et al., 2008).

Increased heat exposure

Heatwaves are associated with marked short-term increases in mortality (Confalonieri et al, 2007). Hot
temperatures have also been associated with increased morbidity. A study  cited in Field et al. (2007)
indicates increased hospital admissions for cardiovascular disease and emergency room visits have been
documented in parts of North  America during heat events.  The populations most  vulnerable to hot
temperatures  are older  adults, the  chronically sick, the very  young,  city-dwellers,  those taking
medications that disrupt thermoregulation, the mentally ill, those lacking access to air conditioning, those
working or playing outdoors, and the socially isolated (Ebi et al., 2008; IPCC, 2007b).

Ebi et al. (2008) report statistics from the Centers for Disease Control and Prevention (CDC, 2005a) that
indicate exposure to excessive natural heat caused 4,780  deaths during the period 1979 to 2002 in the
U.S., and  that an additional 1,203 deaths had hyperthermia reported as a contributing factor.  They state
these numbers are underestimates of the total mortality associated with heat waves because the person
filling out the death certificate may not always list heat as a cause.

Given projections for climate warming, heat-related morbidity and mortality are  projected to increase
globally (including in the U.S.) compared to a future with no climate change (Confalonieri et al, 2007).
Heat exposures vary widely,  and current studies do  not quantify  the years of life  lost  due to  high
temperatures.  Estimates  of heat-related mortality  attributable  to  climate change are reduced but not
eliminated when assumptions about acclimatization and adaptation are included in models.  Confalionieri
et al. (2007) cite  a series of studies that suggests populations  in the U.S.  became  less sensitive to high
temperatures over the period  1964  to 1988, in part, due  to these  factors. On the other hand,  growing
numbers of older adults will increase  the size of the population at  risk because of a decreased ability to
thermo-regulate is a normal part of the aging process (Confalonieri et al, 2007). In addition, according to
a study  in Confalonieri et al. (2007), almost all the growth in population in the next 50 years is expected
to occur in cities where temperatures tend to be higher due to the urban heat island32 effect increasing the
total number of people at risk of adverse health outcomes from heat.  In other words, non-climatic factors
related to demographics will have a significant influence on future heat-related mortality.

Across North America, the population over the age of 65 ~ the segment of the population most at-risk of
dying from heat waves ~ will increase slowly to 2010, and then grow dramatically as the Baby Boomers
age (Field et al., 2007). Severe heat waves are projected to intensify in magnitude and duration over the
portions of the U.S.  where these events  already occur (high confidence).   The IPCC documents the
following  U.S. regional scenario projections of increases in heat and/or heat-related effects (Confalonieri
et al, 2007; Field et al., 2007):
31 According to IPCC terminology, "very likely" conveys a 90 to 99% probability of occurrence. See Box 1.3 on
page 5 for a full description of IPCC's uncertainty terms.
32 A heat island refers to urban air and surface temperatures that are higher than nearby rural areas. Many U.S. cities
and suburbs have air temperatures up to 10°F (5.6°C) warmer than the surrounding natural land cover.
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•   By the 2080s, in Los Angeles, the number of heat wave days (at or above 32°C or 90°F) increases 4-
    fold under the Bl emissions scenario (low growth) and 6-8-fold under A1FI emissions scenario (high
    growth). Annual number of heat-related deaths in Los Angeles increases from about 165 in the 1990s
    to 319 to 1,182 for a range of emissions scenarios.
•   Chicago is projected to experience  25% more frequent heat waves annually by the period spanning
    2080-2099 for a business-as-usual (AIB) emissions scenario.

Reduced cold exposure

Cold waves continue to pose health risks in northern latitudes in temperature regions where  very low
temperatures can be reached in a few  hours  and extend over long periods (Confalonieri et al, 2007).
Accidental cold exposure occurs mainly outdoors,  among  socially deprived people (alcoholics,  the
homeless), workers,  and the elderly in temperate and cold climates but cold waves also affect health in
warmer climates (Confalonieri et al, 2007).  Living in cold environments in polar regions is associated
with a range of chronic conditions in the non-indigenous population with acute risk from frostbite and
hypothermia (Confalonieri et al, 2007).  In countries with populations well-adapted to cold conditions,
cold waves can  still cause  substantial increases  in mortality if electricity  or  heating systems  fail
(Confalonieri et al, 2007).

 Ebi et al.  (2008) cite a study reporting that from 1979 to 2002, an average of 689 reported deaths per year
(range 417-1,021) in the  U.S., totaling  16,555 over the  period, were attributed to exposure to excessive
cold temperatures.

The IPCC projects reduced human mortality from cold exposure through 2100  (Confalonieri et al, 2007).
It is not clear whether reduced mortality from  cold  will be  greater or less than increased heat-related
mortality  in the U.S. due to climate change.   Projections of cold-related deaths, and the potential for
decreasing their numbers due to warmer winters, can be overestimated unless they take into account the
effects of season and influenza, which is not strongly associated with monthly winter temperature (Ebi et
al., 2008;  Confalonieri et al, 2007).

Aggregated changes  in heat and cold exposure

The IPCC (2007) does not explicitly assess studies since the TAR which analyze changes in both heat-
and cold-related mortality in the U.S. in the observed climate or for different future climate scenarios.
However, a study cited in Confalonieri et al. (2007) find existing mortality patterns in U.S.  cities are
relatively  insensitive to temperature variability.  In a future warming climate, this study projects some
mortality  could be reduced  with a  winter-dominant  warming and mortality increase with pronounced
summer warming. Given the paucity of recent literature on the subject and the challenges in estimating
and projecting weather-related mortality, IPCC concludes additional research is needed to understand
how the balance of heat-and cold-related deaths might change globally under different climate  scenarios
(Confalonieri et al, 2007).

7(b)   Extreme Events

In addition to the direct effects of temperature on heat and cold-related  mortality, projected  trends in
climate change-related exposures of importance to human health  will increase the number of people
(globally,  including in the U.S.) suffering from disease and injury due to floods,  storms, droughts and
fires (high confidence) (Confalonieri et al, 2007).  Vulnerability to weather disasters depends on the
attributes  of the people at risk (including where they live, age, income, education, and disability) and on
broader social and environmental factors  (level of disaster preparedness, health sector responses, and
environmental degradation) (Ebi et al., 2008).
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Floods and storms

The  IPCC projects a very likely increase  in heavy precipitation event frequency over most areas  as
described in Sections 6(b and c).  Increases in the frequency of heavy precipitation events are associated
with increased risk of deaths and injuries  as well  as infectious, respiratory and skin diseases (IPCC,
2007b).  Floods  are low-probability, high-impact events that  can  overwhelm physical infrastructure,
human resilience, and social organization (Confalonieri et al, 2007). Flood health impacts include deaths,
injuries,  infectious diseases,  intoxications  and mental  health  problems (Confalonieri  et al,  2007).
Flooding may also lead to contamination of waters with dangerous chemicals, heavy metals, or other
hazardous  substances, from storage or from chemicals already in the environment (Confalonieri et al,
2007).

The  IPCC (2007d) also  projects likely increases in intense tropical cyclone activity as  described  in
Section 6(b). Increases in tropical cyclone intensity  are linked to increases in the risk  of deaths, injuries,
water and foodborne diseases as well as post-traumatic  stress disorders (IPCC, 2007b).  Drowning by
storm surge, heightened by rising sea levels and more intense storms  (as projected by IPCC), is the major
killer in coastal storms where there are large numbers of deaths (Confalonieri et al, 2007).  High-density
populations in low-lying coastal regions such as the U.S.  Gulf of Mexico experience a  high health burden
from weather disasters, particularly among lower income groups.  In 2005,  Hurricane Katrina claimed
over  1800 lives  in  the  vicinity  of the  low-lying  U.S. Gulf  Coast and lower income  groups were
disproportionately affected (Graumann et al., 2005; Nicholls et al., 2007; Confalonieri et al.,  2007). While
Katrina was a Category 3  hurricane and its path was forecast well in advance, there was  a secondary
failure of the levee system. This illustrates that multiple factors contribute to making a disaster and that
adaptation measures may not fully avert adverse consequences (Ebi et al., 2008). Additional information
about U.S. vulnerability to the potential for more intense tropical cyclones can be found in Section 12(b).

Droughts

Areas affected by droughts are likely to increase according to IPCC (2007d) as noted in Section 6(e). The
health impacts  associated with drought tend to most affect semi-arid and arid regions, poor areas and
populations, and areas with human-induced water scarcity;  hence many of these effects are likely to be
experienced in developing countries and not directly in the U.S.  Information about the effects  of
increasing drought on U.S. agriculture can be found in section 9(c).

Wildfires

In some  regions,  changes in the mean and variability of temperature and  precipitation are  projected  to
increase  the size  and severity of fire  events,  including in parts of the U.S.  (Easterling et al.,  2007).
Wildfires can increase  eye and respiratory illnesses and injuries, including burns and smoke inhalation
(Ebi, et al., 2008). A study cited in Confalonieri et al. (2007) indicates large fires are also accompanied by
an increased number of patients seeking emergency  services for inhalation of smoke and ash. The IPCC
(Field et  al., 2007) noted a number of observed changes in  U.S.  wildfire size and frequency. Additional
information on the effects of forest fires can be found in Sections 8(b) and 10(b).

7(c)    Climate-sensitive diseases

The IPCC (2007b) notes that many human diseases  are sensitive to weather.  The incidence of airborne
infectious  diseases (e.g.,  coccidioidomycosis)  varies seasonally and annually, due partly to  climate
variations such as drought, which is projected to increase in the southwestern U.S. (Field  et al.,  2007;
Karl et al., 2008).
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Waterborne disease outbreaks are distinctly seasonal (which suggests potential underlying environmental
or weather control), clustered in particular watersheds, and associated with heavy precipitation. The risk
of infectious disease following flooding in high-income countries is generally low, although increases in
respiratory and diarrheal diseases have been reported after floods (Confalonieri et al, 2007). For example,
after Hurricanes Katrina and Rita in 2005, contamination of water supplies with fecal bacteria led to many
cases of diarrheal illness and some deaths (Ebi et al., 2008; CDC, 2005b; Confalonieri et al, 2007).

Foodborne diseases show some relationship with temperature (e.g., increased temperatures  have been
associated with increased cases of Salmonellosis) (Confalonieri et al, 2007). Vibrio spp. infections from
shellfish  consumption may also be influenced by temperature (Confalonieri et al, 2007).  For example,
Confalonieri et al. (2007) cited a study documenting a 2004 outbreak of Vparahaemolyticus linked to
atypically high temperatures in Alaskan coastal waters.

According to the CCSP (2008b) report, there will likely be an increase in the spread of several food and
water-borne pathogens among susceptible populations depending on the pathogens' survival, persistence,
habitat range and transmission under changing climate and environmental conditions. While the U.S. has
successful programs to protect water quality under the Safe Drinking Water Act and the Clean Water Act,
some contamination pathways and routes of exposure do not fall under regulatory programs (e.g., dermal
absorption from  floodwaters, swimming in lakes and ponds with elevated pathogen  levels, etc.).  The
primary climate-related factors that affect these pathogens include temperature,  precipitation, extreme
weather events,  and shifts in their ecological regimes.   Consistent with our understanding  of  climate
change on human health, the impact of climate on food and water-borne pathogens will seldom be the
only factor determining the burden of human injuries, illness, and death  (CCSP 2008b).

The sensitivity of many zoonotic33 diseases to climate fluctuations is also highlighted by the IPCC (Field
et al., 2007).   A study in Field et al.  (2007)  linked above average temperatures  in the U.S.  during the
summers of 2002-2004 to the greatest transmissions of West Nile virus. Saint Louis  encephalitis has a
tendency to appear during hot, dry La  Nina years according to a study cited in Field et al.  (2007).
Associations between temperature and precipitation and tick-borne Lyme disease are also  noted by IPCC
(Field et al., 2007).  A study cited in Field et al. (2007) found that the northern range limit of Ixodes
scapularis, the tick that carries Lyme disease,  could shift north by 200  km by the 2020s and 1000 km by
the 2080s.

Although large portions of the U.S. may be at potential risk for diseases such as malaria based on the
distribution of competent disease vectors, locally acquired cases have  been virtually eliminated, in part
due to effective public health interventions, including vector and disease  control activities.  (Ebi et al.,
2008; Confalonieri et al, 2007).

The IPCC concludes that human health risks from climate change will be strongly modulated by changes
in health care,  infrastructure, technology, and accessibility to health care (Field et al., 2007).  The aging of
the population and patterns of immigration and/or emigration will also strongly influence risks (Field et
al., 2007).

7(d)   Aeroallergens

Climate change, including changes in CO2 concentrations, could impact the production, distribution,
dispersion and allergenicity of aeroallergens and the growth and distribution of weeds, grasses and trees
that produce them (McMichael. et al., 2001; Confalonieri et al., 2007). These changes in aeroallergens
33A zoonotic disease is any infectious disease that is able to be transmitted from an animal or nonhuman species to
humans. The natural reservoir is a nonhuman reservoir.
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and  subsequent human  exposures  could affect  the prevalence  and  severity of allergy symptoms.
However, the scientific literature does not provide definitive data or conclusions on how climate change
might impact aeroallergens and subsequently the prevalence of allergenic illnesses in the U.S. In addition,
there are numerous other factors that affect aeroallergen levels and the prevalence of associated allergenic
illnesses, such as changes in land use, air pollution, and adaptive responses, many of which are difficult to
assess (Ebi et al., 2008).

It  has  generally been observed that  the presence  of elevated CO2 concentrations  and temperatures
stimulates plants to increase photosynthesis, biomass, water use efficiency, and reproductive effort. The
IPCC concluded that pollens are likely to increase with elevated temperature and CO2 (Field et al., 2007).
Laboratory studies cited by Field et al. (2007) stimulated ragweed-pollen production by over 50% using a
doubling of CO2   A  U.S.-based field study  referenced by  Field et al. (2007)  which  used  existing
temperature/CO2 concentration differences between urban and rural areas  as a proxy for climate change
found that ragweed grew faster, flowered earlier, and produced significantly greater aboveground biomass
and ragweed pollen at urban locations than at rural locations.

The  IPCC (Confalonieri et al, 2007) noted that climate change  has  caused an earlier onset of the spring
pollen season in North America and that there is limited evidence that the length of the pollen season has
increased for some species.  However, it is unclear whether the allergenic content of these pollens has
changed.  The  IPCC  concluded that introductions of new invasive plant species with high allergenic
pollen  present  important health risks, noting  that ragweed (Ambrosia artemisiifolia) is spreading in
several parts of the world (Confalonieri et al, 2007).
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Section 8

Air Quality

Surface air concentrations of air pollutants  are highly sensitive to winds,  temperature, humidity and
precipitation (Denman et al., 2007).  Climate change can be expected to influence the concentration and
distribution of air pollutants through a variety of direct and indirect processes, including the modification
of biogenic emissions, the change of chemical reaction rates, wash-out of pollutants by precipitation, and
modification  of weather patterns  that influence pollutant buildup.  In summarizing the impact of climate
change on ozone and particulate matter (PM), the IPCC (Denman et al., 2007) states that "future climate
change may cause significant air quality degradation by changing the dispersion rate of pollutants, the
chemical environment for ozone  and PM generation and the strength of emissions from the biosphere,
fires and dust."

This section  describes  how  climate change  may alter ambient  concentrations  of ozone and PM with
associated impacts on public health and welfare in the U.S.

8(a)    Tropospheric Ozone

According to the IPCC (Denman  et al., 2007), climate change is expected to lead to increases in regional
ozone pollution in the U.S. and other countries. Ozone impacts on pubic health and welfare are described
in EPA's Air Quality  Criteria  Document  for  Ozone  (EPA,  2006).  Breathing ozone  at  sufficient
concentrations can  reduce lung  function, thereby aggravating asthma or other respiratory conditions.
Ozone exposure at  sufficient concentrations  has been associated with increases in respiratory infection
susceptibility, medicine use by asthmatics, emergency department visits and hospital admissions. Ozone
exposure may contribute to premature  death,  especially in susceptible populations.  In contrast to human
health effects, which are associated with short-term exposures, the most significant ozone-induced plant
effects (e.g.,  biomass loss, yield  reductions)  result from the accumulation of ozone exposures over the
growing  season, with differentially greater  impact resulting from exposures to  higher concentrations
and/or longer durations.

Tropospheric ozone is  both naturally occurring and,  as  the primary constituent of urban  smog, a
secondary pollutant formed through  photochemical  reactions involving nitrogen oxides  (NOx) and
volatile organic compounds (VOCs)  in the presence of sunlight. As described below, climate change can
affect ozone by modifying (1) emissions of precursors, (2) atmospheric chemistry, and (3) transport and
removal (Denman et al., 2007).  There is now consistent evidence from models and observations that
21st-century climate change will worsen summertime surface ozone in polluted regions of North America
compared to a future with no climate change (Jacob and Winner, 2009).

The IPCC (Denman et al., 2007)  states that, for all world regions, "climate change affects the sources of
ozone  precursors through physical response (lightning),  biological response  (soils,  vegetation, and
biomass burning) and human response (energy generation, land use,  and agriculture)." Nitrogen oxides
emissions due  to  lightning  are  expected to increase  in  a warmer climate  (Denman  et al., 2007).
Additionally, studies using general circulation models concur that influx of ozone from the stratosphere to
the troposphere could increase due to large-scale atmospheric circulation shifts (i.e., the Brewer-Dobson
circulation) in response to climate warming (Denman et al., 2007). The sensitivity of microbial activity in
soils to temperature also points toward a substantial increase in the nitric oxide emissions (Brasseur et al.,
2006). As described below, biogenic VOC emissions increase with increasing temperature.
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Climate induced changes of biogenic VOC  emissions alone may be regionally substantial and cause
significant increases in ozone concentrations  (Hauglustaine et al., 2005; Hogrefe et al., 2004; European
Commission, 2003). Sensitivity simulations  for the 2050s, relative to the 1990s suggest under the A2
(high-end) climate scenario that increased biogenic emissions alone add 1-3 parts per billion  (ppb) to
summertime average daily maximum 8-hour ozone concentrations in the Midwest and along the eastern
seaboard (Hogrefe et al., 2004).  The IPCC (Meehl et al., 2007)  reports that biogenic  emissions are
projected to increase by between 27 and 59%, contributing to a 30 to 50% increase in ozone formation
over northern continental regions (for the 2090-2100 timeframe, relative to 1990-2000).

Consistent with this, for nearly all simulations in the EPA  Interim Assessment (2009), climate change is
associated with increases in biogenic VOC emissions over most of the U.S., with especially pronounced
increases in the Southeast.  These biogenic emissions increases do not necessarily correspond with ozone
concentration increases, however. The report suggests that the response of ozone to changes in biogenic
emissions depends on how isoprene chemistry is represented in the models—models that recycle  isoprene
nitrates back to NOx will tend to simulate significant O3 concentration increases in regions with biogenic
emissions increases, while models  that do not recycle isoprene nitrates will  tend to simulate small
changes, or even O3 decreases.

Climate change impacts on temperature could affect ozone  chemistry significantly (Denman et al., 2007).
A number of studies in the U.S. have shown that summer daytime ozone concentrations correlate strongly
with temperature. That is, ozone generally increases at higher temperatures. This correlation appears to
reflect contributions of comparable magnitude from  (1) temperature-dependent biogenic VOC emissions,
as mentioned above, (2) thermal decomposition of peroxyacetylnitrate (PAN), which acts as a reservoir
for NOx, as described immediately below, and (3)  association of high temperatures  with  regional
stagnation, also discussed below (Denman et al., 2007).

The EPA Interim Assessment (2009), however, reports that considering a single meteorological variable,
such as temperature, may not provide a sufficient basis  for determining future ozone  risks due to climate
change in every region. This is  consistent with the potential for different competing effects in different
regions.  The modeling studies  found some regions of the country  where simulated increases  in cloud
cover, and hence decreases in the amount of sunlight reaching the surface, partially counteracted the
effects of warming  temperatures on ozone concentrations in these regions, to go along with the many
regions where the effects of temperature and cloud cover reinforced each other in producing O3 increases.

Climate change is projected to  increase  surface  layer ozone concentrations in both urban and  polluted
rural environments  due to decomposition of PAN at higher temperatures (Sillman  and Samson, 1995;
Liao and Seinfeld, 2006). Warming enhances decomposition of PAN, releasing NOx, an important ozone
precursor (Stevenson et al., 2005).  Model simulations  (using the high-end A2 emissions scenario) with
higher temperatures for the year 2100 showed that enhanced PAN thermal  decomposition caused this
species to decrease by up to 50% over source  regions and ozone net production to increase (Hauglustaine
et al., 2005).

Atmospheric circulation can be expected to  change in a  warming  climate and, thus, modify pollutant
transport and removal.  The CCSP (2008b) reports that stagnant air masses related to climate change are
likely to degrade air quality in some densely populated  areas.  More frequent occurrences of stagnant air
events in urban or  industrial areas could enhance the intensity  of air pollution events,  although the
importance of these  effects is not yet well quantified (Denman et al., 2007). The IPCC (2007d) concluded
that  "extra-tropical  storm tracks are projected to move poleward,  with consequent changes in wind,
precipitation, and temperature patterns, continuing the broad pattern of observed trends over the last half-
century."
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The IPCC (Denman et al, 2007) cites a study for the eastern U.S. which found an increase in the severity
and persistence of regional pollution episodes due to the reduced  frequency of ventilation by storms
tracking across Canada.  This study found that surface cyclone activity decreased by approximately 10-
20% in a future  simulation (for 2050, under the mid-range IPCC A1B scenario),  in general agreement
with a number of observational studies over the northern midlatitudes and North America. Northeast U.S.
summer pollution episodes are projected in this study to increase in severity and duration; pollutant
concentrations in episodes increase 5-10% and episode durations increase from 2 to 3-4 days.  Analysis of
historical data supports both the trend in decreasing frequency of ventilation and the increase in summer
pollution episodes (Leibensperger et al., 2008).

Regarding the role water vapor plays in tropospheric ozone formation, the IPCC (Denman et al., 2007)
reports that simulations for the 21st century indicate a decrease in the lifetime of tropospheric ozone due
to increasing  water vapor.   The  projected  increase  in  water vapor both decelerates  the  chemical
production and accelerates the chemical destruction of ozone (Meehl et al., 2007). Overall, the IPCC
states that climate change  is expected to decrease background tropospheric ozone due to higher water
vapor and to increase regional and urban-scale ozone pollution due to higher temperatures and weaker air
circulation (Denman et al., 2007; Confalonieri et al., 2007).

For North America, the IPCC (Field et al., 2007) reports that surface ozone concentration may increase
with a warmer climate.  For the continental U.S., the CCSP  (2008b) report states that the northern
latitudes are likely to experience the largest increases in average temperatures and they will also bear the
brunt of increases in ground-level ozone and other airborne pollutants.

Modeling  studies discussed in EPA's Interim Assessment (2009) show that simulated climate change
causes increases  in  summertime O3 concentrations over substantial regions of the  country,  though this
was  not uniform, and some areas  showed  little change or decreases. For  those regions that showed
climate-induced increases, the increase in Maximum Daily 8-hour Average O3 concentration, a key metric
for regulating U.S.  air quality, was in the range  of 2-8 ppb, averaged over the  summer season.  The
increases were substantially greater than this during the peak pollution episodes that tend to occur over a
number of days each summer. While the results  from the different research groups agreed on the above
points, their modeling systems did not always simulate the same regional patterns of climate-induced O3
changes across the U.S. Certain regions show greater agreement than others: for example, there is more
agreement on climate-induced increases for the eastern half of the country than for the West.  Parts of the
Southeast  also show strong disagreements  across the modeling groups. Where  climate-change-induced
increases in  ozone do occur, damaging effects on ecosystems, agriculture, and health are expected to be
especially pronounced, due to increases in the frequency of extreme pollution events.

The EPA Interim Assessment (2009) suggests that climate change effects on ozone grow continuously
over time, with evidence for significant increases emerging  as early as the 2020s.  The EPA Interim
Assessment  (2009) and the IPCC (Field et al., 2007; Wilbanks et al., 2007) cite a study which evaluates
the effects of climate change on regional ozone in  15 U.S. cities, finding that average summertime daily
8-hour maximum ozone concentrations could increase by 2.7 ppb in the 2020s and by 4.2 ppb in the
2050s under the A2 (high-end) scenario.

Studies reviewed in EPA's Interim Assessment (2009) and Jacob and Winner (2009) indicate the largest
increases in  ozone concentrations due to climate change occur during peak pollution events.  Mickley et
al. (2004) find that climate change projected to occur under the A IB (mid-range) scenario results in
significant changes that occur at the high end of the pollutant  concentration distribution (episodes) in the
Midwest  and Northeast between 2000 and  2050 given constant levels of criteria pollutant emissions.
Using the A2 (high-end) emissions scenario, Hogrefe et al. (2004) find that while regional climate change
in the eastern U.S. causes the summer average daily maximum 8-hour ozone concentrations to increase by
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2.7, 4.2, and 5.0 ppb in 2020s, 2050s, and 2080s (compared to 1990s), regional climate changes causes
the fourth highest summertime daily maximum 8-hour ozone concentrations to increase by 5.0, 6.4, and
8.2 ppb for the 2020s,  2050s, and 2080s, respectively (compared to  1990s) (Hogrefe et al., 2004).  The
CCSP (2008b) also reports climate change is projected to have a much greater impact on extreme values
and to shift the distribution of ozone concentrations towards higher values, with larger relative increases
in future decades. In addition, simulations reviewed in the EPA Interim Assessment (2009) showed that,
for parts of the country with a defined summertime O3 season, climate change expanded its duration into
the fall and spring. These findings raise particular health concerns.

The IPCC (Field et al.,  2007) states that, "warming and climate extremes are likely to increase respiratory
illness, including exposure to pollen and ozone."  And the IPCC further  states that "severe heat waves,
characterized by stagnant, warm air masses and consecutive nights with high minimum temperatures will
intensify in magnitude  and duration over the portions of the U.S. and Canada, where they already occur
(high confidence) (Field et al., 2007)." Further, as described in CCSP (2008b), there is some evidence that
combined effects of heat stress and air pollution may be greater than simple additive effects and historical
data show relationships between mortality and temperature extremes.

Holding population, dose-response characteristics, and pollution prevention measures constant, ozone-
related deaths  from climate change in the New York City metropolitan area are projected to increase by
approximately 4.5% from the 1990s to the 2050s (under the high-end IPCC A2 scenario) (Field  et al.,
2007).  According to the IPCC (Field et al., 2007), the "large potential population exposed to outdoor air
pollution, translates this small relative risk into a substantial attributable health risk." In New York City,
health impacts could be further exacerbated by climate change interacting with urban heat island effects
(Field et al., 2007).  For A2 scenario in the 2050s, Bell et al. (2007) report that the projected effects of
climate change on ozone in 50 eastern U.S. cities increased the number of summer days exceeding  the 8-
hour U.S.  EPA standard by 68%.  On average across the 50 cities, the summertime daily 8-h maximum
increased 4.4 ppb. Elevated ozone levels correspond to approximately a 0.11% to 0.27% increase in daily
total mortality.  The  largest ozone increases  are estimated to occur in cities with present-day high
pollution.

As noted in CCSP (2008b), the influence of climate change on air quality will play out against a backdrop
of ongoing  regulatory  control of both ozone and particulate matter (PM) that will shift the  baseline
concentrations of these two important pollutants. The range of plausible short-lived emissions projections
is very large.  For example, emission projections  used in CCSP (2008d) and in the Fourth Assessment
Report of the IPCC differ on whether black carbon particle and nitrogen oxides emissions trends continue
to increase  or decrease. Improvements in our ability to project social, economic and technological
developments affecting future emissions are needed.  However, most studies to  date that have examined
potential future climate change impacts on air quality isolate the climate  effect  by holding precursor air
pollutant emissions constant over time.

The IPCC  reports (Denman et al., 2007) that "the current generation of tropospheric ozone models is
generally successful in  describing  the principal features of the  present-day global ozone distribution."
The IPCC (Denman et  al., 2007) also states that "there are major discrepancies with observed long-term
trends in ozone  concentrations over the 20th century" and "resolving these discrepancies is needed to
establish confidence in the models."

In addition to human health effects, elevated levels of tropospheric ozone  have significant adverse effects
on crop yields in the U.S. and other world regions, pasture and forest growth and species composition
(Easterling et al., 2007). Furthermore, the effects of air pollution on  plant function may indirectly affect
carbon storage; recent research showed that tropospheric ozone resulted in significantly less enhancement
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of carbon sequestration rates under elevated CO2, due  to  negative  effects of ozone on  biomass
productivity and changes in litter chemistry (Easterling et al., 2007).

8(b)   Particulate Matter

Particulate matter (PM) impacts on public health and welfare are described in EPA's Air Quality Criteria
Document for Particulate Matter (EPA, 2004).  Particulate matter is  a complex mixture of anthropogenic,
biogenic  and natural materials, suspended as  aerosol particles in the atmosphere.  When inhaled, the
smallest of these  particles can reach the deepest regions of the lungs. Scientific studies have found an
association between exposure to  PM and significant health problems,  including: aggravated asthma;
chronic bronchitis; reduced lung function; irregular heartbeat; heart attack; and premature death in people
with heart or lung disease.  Particle  pollution also  is the  main cause of visibility impairment  in the
nation's cities and national parks.

The overall directional impact of climate change on PM levels in the U.S. remains uncertain   (National
Assessment, 2008), as too few data yet exist for PM to draw firm conclusions about the direction or
magnitude of climate impacts  (CCSP, 2008b).  However, preliminary  results of modeling  analyses
reported  in the EPA Interim Assessment (2009) are listed below.  These  analyses show a range of
increases and decreases in PM concentrations in different regions and for different component chemical
species in the same region:

    1.  Precipitation is a more important primary meteorological driver of PM than of O3, due to its role
       in removing PM from the atmosphere (wet  deposition). Precipitation, however,  is  particularly
       difficult to model and shows greater disagreement across simulations than other variables.
    2.  Aerosol chemical processes, especially those concerning the formation  of organic aerosols, are
       not fully understood and therefore not well characterized in current regional air quality models.
    3.  Preliminary simulation results suggest that,  globally, PM  generally decreases  as  a result of
       simulated climate change,  due to increased atmospheric humidity and increased precipitation.
    4.  Regionally, simulated 2050 climate change produces both increases and decreases in PM (on the
       order of a few percent), depending on region. For the U.S., the largest simulated increases are
       found in the Midwest and Northeast.
    5.  This PM response reflects the combined climate change responses of the individual species that
       make up PM (e.g., sulfate, nitrate, ammonium, black carbon, organic carbon, etc.). Depending on
       the region, these individual responses can be in competing directions.
    6.  Increase in wildfire frequency associated with a warmer climate has the potential to increase PM
       levels in certain regions.

Further, Jacob and Winner (2009) summarize the current state of knowledge as:

"The response of  PM to climate change is more complicated than that for ozone because of the diversity
of PM components, compensating effects, and general uncertainty in GCM projections of the  future
hydrological  cycle. Observations  show little useful correlation of  PM with climate variables to guide
inferences of the effect of climate change. Rising temperature is expected to have a mild negative effect
on PM due  to volatilization of  semi-volatile components (nitrate, organic),  partly  compensated by
increasing sulfate  production. Increasing stagnation should cause PM to increase. Precipitation frequency,
which  largely determines PM loss, is expected to increase globally but to decrease in southern North
America and southern Europe. PM is highly sensitive to mixing depths but there is no consensus among
models on how these will respond to climate change... Increases in wildfires driven by climate change
could significantly increase PM concentrations beyond the direct  effect of changes in  meteorological
variables."
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PM and PM precursor emissions are affected by climate change through physical response (wind blown
dust), biological response (forest fires and  vegetation type/distribution) and human response (energy
generation). Most natural aerosol sources are controlled by climatic parameters like wind, moisture and
temperature; thus, human induced  climate  change is expected to affect the natural  aerosol burden.
Biogenic organic material is both directly  emitted into the atmosphere and produced by VOCs.  All
biogenic VOC emissions are highly sensitive to changes in temperature, and are also highly sensitive to
climate-induced changes in plant species composition and biomass distributions.  Denman et al. (2007)
cite a study in which biogenic emissions rates are predicted to increase, on average across world regions,
by 10% per 1°C increase in surface temperature.  The response of biogenic secondary organic carbon
aerosol production to a temperature change,  however, could be considerably lower than the response of
biogenic VOC emissions since aerosol yields can decrease with increasing temperature (Denman et al.,
2007).

Particulate matter emissions from forest fires can  contribute  to  acute and chronic  illnesses of the
respiratory system, particularly in children, including  pneumonia, upper respiratory diseases, asthma and
chronic  obstructive pulmonary diseases (WHO, 2002; Bowman and Johnston, 2005; Moore et al., 2006;
Confalonieri et al., 2007). The IPCC (Field et al., 2007) reported with very high confidence that in North
America disturbances like wildfire are increasing and  are likely to intensify in a warmer future with drier
soils and  longer  growing seasons.   Forest  fires  with their associated decrements to air  quality and
pulmonary effects are likely to increase in frequency, severity, distribution, and duration in the Southeast,
the Intermountain West  and the West compared to  a future with no climate change  (CCSP, 2008b).
Pollutants from forest fires can affect air quality for thousands of kilometers (Confalonieri et al., 2007).
A study cited in Field et al. (2007) found that, in the last three decades, the wildfire season in the western
U.S. has increased by 78 days, and burn durations of  large fires have increased from 7.5 to 37.1 days, in
response to a spring-summer warming of 0.87°C.  It also found earlier spring snowmelt has led to longer
growing seasons and drought, especially at higher elevations, where the increase in wildfire activity has
been greatest.  Analysis by the State of California suggests that large wildfires could become up to 55%
more frequent in some areas toward the end  of the century due to continued global warming (California
Climate Change Center,  2006).

PM  chemistry is affected by changes  in temperature brought  about  by climate change  as follows.
Temperature  is one  of  the most important meteorological variables influencing  air quality in urban
atmospheres because it directly affects gas and heterogeneous chemical reaction rates and gas-to-particle
partitioning. The net effect that increased temperature has on airborne particle concentrations is a balance
between increased production rates for secondary particulate matter  (increases particulate concentrations)
and increased equilibrium vapor pressures for semi-volatile particulate compounds (decreases particulate
concentrations). Increased temperatures may either increase or decrease the concentration of semi-volatile
secondary reaction products such as ammonium nitrate depending on ambient conditions.

Denman et al., 2007 note that there has been less work on  the sensitivity of aerosols to meteorological
conditions.  It cites  a  study  that produces regional model simulations for Southern  California on
September 25,  1996 projecting decreases  in 24-hour average  PM2s  concentrations  with increasing
temperatures for inland portions of the South Coast air basin, and projecting increases for coastal regions.
In CCSP (2008b), using the NYCHP integrated model, PM25 concentrations are projected to increase
with climate  change, with the effects differing by component species, with sulfates  and primary PM
increasing markedly  and with organic and nitrated components decreasing, mainly due to movement of
these volatile species from the particulate to the gaseous phase.

The transport and removal of PM is highly sensitive to winds and precipitation. Removal of PM from the
atmosphere occurs mainly by wet deposition (NAS, 2005).  Sulfate  lifetime, for example, is estimated to
be reduced from 4.7  days to 4.0 days  as a result of increased wet deposition (Liao and Seinfeld, 2006).
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Precipitation also affects  soil  moisture,  with impacts  on  dust source  strength and on  stomatal
opening/closure of plant leaves, hence affecting biogenic emissions (Denman et al., 2007). Precipitation
has generally increased over land  north  of 30°N  over the period  1900 to 2005  and it has  become
significantly wetter in eastern parts of North America (Trenberth  et  al.,  2007).    However, model
parameterizations of wet deposition are highly uncertain and not fully realistic in their coupling to the
hydrological cycle (NAS, 2005).  For  models to simulate accurately the seasonally varying pattern of
precipitation, they must correctly simulate  a number of processes (e.g., evapotranspiration, condensation,
transport) that are difficult to evaluate at a global scale (Randall et al., 2007).

In 1997 (62 FR 38680), EPA concluded that participate matter produces adverse effects on visibility, and
that visibility impairment is experienced (though not necessarily attributed to climate change) throughout
the U.S., in multi-state regions, urban areas, and remote Federal Class I areas34. Visibility impairment
depends  strongly on ambient relative humidity (NARSTO, 2004). Although surface specific humidity
globally has generally increased after 1976 in close association with higher temperatures over both land
and ocean, observations suggest that relative humidity has remained about the same overall, from the
surface  throughout the troposphere  (Trenberth et  al., 2007).  Nevertheless,  increases in PM due to
increases in wildfires induced by climate change might increase visibility  impairment.

8(c)    Health Effects due to CO2-Induced Increases in Tropospheric O3 and Particulate Matter

In addition to  the analyses described above  of climate  change impacts  on air quality, one  study
specifically examined the more direct effect of CO2 on air pollution mortality.  As described in the CCSP
(2008b) report, using a coupled climate-air pollution three-dimensional model, a study compared the
health effects of pre-industrial vs. present-day atmospheric concentrations of CO2.  The results  suggest
that increasing concentrations of CO2 increased tropospheric ozone and PM2 5, which increased mortality
by about 1.1% per degree temperature increase over the baseline rate;  the study estimated that about 40%
of the increase was due to ozone and the rest to particulate matter.  The estimated mortality increase was
higher in locations with poorer air quality.
34 The Clean Air Act defines mandatory Federal Class I areas as certain national parks (over 6,000 acres), wilderness
areas (over 5,000 acres), national memorial parks (over 5,000 acres), and international parks that were in existence
as of August 7, 1977.
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Section 9

Food Production and Agriculture

Food production and the agricultural sector within the U.S. are sensitive to short-term climate variability
and long-term climate change.  This section addresses how observed and projected climate change may
affect U.S. food production and agriculture. Food production and agriculture here include crop yields and
production, livestock production (e.g., milk and meat), freshwater fisheries,  and key climate-sensitive
issues for this sector including drought risk and pests and weeds.

In addition to changes in average temperatures and precipitation patterns, this section also addresses how
U.S. food production and agriculture may be affected directly by elevated CO2 levels, as well as the
frequency and severity of extreme  events, such as droughts and storms. Climate change-induced effects
on tropospheric ozone levels and their impacts on agriculture are discussed briefly in Section 8 on Air
Quality.

Vulnerability of the U.S. agricultural sector  to climate change is a function of many interacting factors
including pre-existing climatic  and soil conditions, changes  in pest competition, water availability, and
the sector's capacity to cope and adapt through management  practices, seed and  cultivar technology, and
changes in economic competition among regions.

The CCSP report on U.S. agriculture (Backlund et al., 2008a) made the following general conclusions for
the U.S.:

    •  With increased CO2 and temperature, the life cycle of grain and oilseed crops will likely progress
       more rapidly. But, as temperature rises, these crops will increasingly begin to experience failure,
       especially if climate variability  increases and precipitation lessens or becomes more variable.

    •  The marketable yield of many horticultural crops - e.g., tomatoes, onions, fruits - is very likely to
       be more sensitive to climate change than grain and oilseed crops.

    •  Climate change is likely to lead  to a northern migration of weeds. Many weeds respond more
       positively to increasing CO2 than most cash crops, particularly C3 "invasive" weeds35. Recent
       research also suggests  that glyphosate, the most widely used herbicide in the U.S., loses  its
       efficacy on weeds grown at the  increased CO2 levels likely in the coming decades.

    •  Disease pressure on crops  and domestic animals will likely  increase with earlier springs and
       warmer winters,  which will allow  proliferation and  higher  survival  rates  of pathogens and
       parasites.  Regional variation  in warming and  changes in rainfall will also affect spatial and
       temporal distribution of disease.

    •  Projected increases in temperature and a lengthening of the growing season will likely extend
       forage production into late  fall and early spring, thereby decreasing need for winter season forage
       reserves. However, these benefits will very  likely be affected by regional variations in  water
       availability.
35 C3 and C4 refer to different carbon fixation pathways in plants during photosynthesis. C3 is the most common
pathway, and C3 crops (e.g., wheat, soybeans and rice) are more responsive than C4 crops such as maize.
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    •   Climate  change-induced  shifts  in  plant  species  are  already  underway  in  rangelands.
        Establishment of perennial herbaceous species  is reducing soil water availability  early in the
        growing season. Shifts in plant productivity and type  will likely also have significant impact on
        livestock operations.

    •   Higher temperatures will very likely reduce livestock  production during the  summer season, but
        these losses will very likely be partially offset by warmer temperatures during the winter season.
        For ruminants, current management systems generally  do not provide shelter to buffer the adverse
        effects of changing climate; such protection is more frequently available for non-ruminants (e.g.,
        swine and poultry).

The IPCC (2007b) made  the following  general conclusion about food production and agriculture for
North America:

    •   Moderate climate  change in the early decades of the  century is projected to increase aggregate
        yields of rainfed agriculture by 5-20%, but with important variability  among regions. Major
        challenges are projected for crops that are near the warm end of their suitable range or  depend on
        highly utilized water resources [high confidence].36

9(a)    Crop yields and productivity

    •   Observational evidence shows that, over the last century, aggregate yields of major U.S. crops
        have been increasing (USDA, 2007; Field et al., 2007), with significant regional and temporal
        variation. Multiple factors contribute to these long term  trends, including seed technology, use of
        fertilizers, management practices, and climate change (e.g., lengthening of the growing  season).

For projected climate change effects, the IPCC summary conclusion of net beneficial effects in the early
decades in the U.S. under moderate climate change, with significant regional variation, is supported by a
number of recent assessments for most major crops, and is  consistent with the previous  IPCC  Third
Assessment (2001) conclusion.37  Moderate climate change  for temperate regions  such as the U.S. is
described as local increases in temperature of 1-3°C (~2-5°F), which may occur within the next few
decades or past mid-century depending on scenario  (see Section 6 for temperature projections).  Increased
average warming leads to an extended growing  season, especially for northern regions  of the  U.S.
Further warming, however, is projected  to have increasingly negative impacts in all  regions  (meaning
both temperate, including the U.S., and tropical regions of the world) (Easterling et al. 2007).

The CCSP report on agriculture (Hatfield et al., 2008) provides further crop-specific detail about optimum
temperatures in order to assess the effects of future climate change. Crops are characterized by an upper
failure-point  temperature at which pollination and grain-set  processes fail. Considering these aspects,
Hatfield et al., (2008) detail the  following optimum mean temperatures for grain yields of the major
agronomic crops: 18-22°C  for maize, 22-24°C for  soybean, 15°C for wheat, 23-26°C  for rice, 25°C for
sorghum, 25-26°C for cotton, 20-26°C for peanut, 23-24°C for dry bean, and 22-25°C for tomato.
36 According to IPCC terminology, "high confidence" conveys an 8 out of 10 chance of being correct. See Box 1.3
on page 5 for a full description of IPCC's uncertainty terms.
37 The North America chapter from the IPCC Third Assessment Report (Cohen et al. 2007) concluded: "Food
production is projected to benefit from a warmer climate, but there probably will be strong regional effects, with
some areas in North America suffering significant loss of comparative advantage to other regions (high
confidence)."
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Given the variable responses of different crops to temperature (and other climatic) changes, and the fact
that different areas of the country specialize in different crops and have different regional climates, the
variable future climate change effects among regions and crops  are important to consider.  The  south-
eastern U.S. may be more vulnerable to increases in average temperature than more northern regions due
to pre-existing temperatures that are already relatively high.  Likewise, certain crops that are currently
near climate thresholds (e.g., wine grapes in California)  are likely to experience  decreases in yields,
quality, or both, even under moderate climate change scenarios (Field et al, 2007).

Without the benefit of CO2, the anticipated 1.2°C rise in temperature over the next 30 years (a baseline
assumption assumed in the CCSP (Hatfield et al.,  2008)  report)  is projected to decrease  maize, wheat,
sorghum,  and dry bean yields by 4.0, 6.7,  9.4, and 8.6 percent,  respectively, in  their major production
regions. For soybean, the  1.2°C temperature rise will increase yield 2.5 percent in the Midwest  where
temperatures during July, August, September average 22.5°C, but will decrease yield 3.5  percent in the
South, where mean temperature during July, August, and  September averages 26.7°C. Likewise,  in the
South, that same mean temperature will result in reduced rice, cotton, and peanut yields, which will de-
crease 12.0, 5.7, and 5.4 percent, respectively (Hatfield et al., 2008).  An anticipated CO2 increase from
380 to 440 ppm will increase maize and sorghum yield by only 1 percent, whereas the listed C3 crops will
increase yield by 6.1 to 7.4 percent, except for cotton, which shows a 9.2 percent increase (Hatfield et al.,
2008).

Changes in precipitation patterns will play a large role in determining the net impacts of climate change at
the national and sub-national  scales, where uncertainties about precipitation changes remain very large.
The IPCC (Field et al., 2007) reviewed integrated assessment modeling studies exploring the interacting
impacts of climate and economic factors on agriculture, water resources, and biome boundaries  in the
U.S. and concluded that scenarios with decreased precipitation create important challenges, restricting the
availability of water for irrigation and at the same time increasing water demand for irrigated agriculture,
as well as urban and ecological uses. The critical importance of specific agro-climatic events, such  as last
frost, also introduces uncertainty in future projections (Field et al., 2007).

There is still uncertainty about the sensitivity of crop yields in the U.S. and other world  regions  to the
direct effects of elevated CO2 levels.  The IPCC (Easterling et al., 2007) concluded that elevated  CO2
levels are expected to  contribute to small  beneficial  impacts  on  crop yields.  The IPCC  confirmed the
general conclusions from its previous Third Assessment Report in 2001. Experimental research on crop
responses to elevated CO2 through the FACE (Free Air CO2 Enrichment)38 experiments indicate that,  at
ambient CO2 concentrations of 550 ppm  (approximately  double the concentration from pre-industrial
times), crop yields increase under unstressed conditions by 10-25% for C3 crops, and by  0-10% for C4
crops (medium confidence). Crop model simulations under elevated CO2 are consistent with these ranges
(high confidence) (Easterling et al., 2007).  High temperatures, water and nutrient availability, and ozone
exposure, however, can significantly limit the direct stimulatory CO2 response.

Hatfield et al. (2008) provides  further detail about individual crop species responses to elevated  CO2
concentrations and the  interactive effects with other climate change factors. Overall, the benefits of CO2
rise over the next 30 years are projected to mostly offset the negative effects of temperature for most C3
crops except rice and bean,  while the C4 crop yields are reduced by rising temperature because they have
little response to the CO2 rise (Hatfield et al., 2008). Thus, according to Hatfield et al. (2008), the 30-year
outlook for U.S. crop production is relatively neutral. However, the outlook for U.S. crop production over
the next 100 years would not be as optimistic, if temperature  continues to rise along with climbing  CO2
concentrations, because the C3 response to rising CO2 is reaching a saturating plateau, while the negative
temperature effects will become progressively more severe (Hatfield et al.,  2008).
38
  http://www.bnl.gov/face/
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There are continual changes in the genetic resources of crop varieties and horticultural crops that will
provide increases in yield due to increased  resistance to water and pest stresses. These  need to be
considered in any future assessments of the climatic impacts; however, the genetic modifications have not
altered the basic temperature response or CO2 response of the biological system (Hatfield et al., 2008).

Although horticultural crops (fruits, vegetables and nuts) account for more than 40 percent of total crop
market value in the U.S. (2002 Census of Agriculture), there is relatively little information  on their re-
sponse to CO2, and few reliable crop simulation models for use in climate change assessments compared
to that which is available for major grain and oilseed crops (Hatfield et al., 2008). The marketable yield of
many horticultural crops is likely to be more sensitive to climate change than grain and oilseed crops
because even  short-term, minor environmental  stresses can  negatively affect visual and flavor quality
(Hatfield et al., 2008).

9(b)   Irrigation requirements

The impacts of climate change on irrigation water requirements  may be large (Easterling et al., 2007).
The IPCC considered this to be a new, robust finding since the Third Assessment Report in 2001.  The
increase in irrigation demand due to climate change is expected in the majority of world regions including
the U.S.  due to decreased rainfall in certain regions and/or increased evaporation arising from increased
temperatures.   Longer growing seasons may contribute  to  the  increased irrigation  demands as  well.
Hatfield et al.  (2008) describe in the CCSP report studies that examined changes in irrigation  requires for
the U.S. under climate  change scenarios.  For corn, a study cited  in Hatfield et al. (2008) calculated that
by  2030  irrigation requirements will change from -1 (Lower Colorado Basin) to +451 percent (Lower
Mississippi Basin), because of rainfall variation. Given the variation in the sizes and  baseline irrigation
requirements of U.S. basins, a representative figure for the  overall U.S. increase in irrigation requirements
is 64 percent if stomatal effects are ignored, or 35  percent if they are included. Similar calculations were
made for alfalfa, for which overall irrigation requirements are predicted to increase 50 and 29 percent in
the next 30 years in the cases of ignoring and including stomatal effects, respectively. These increases are
more  likely  due to the decrease in rainfall during the growing season and the  reduction in soil water
availability.

9(c)   Climate variability and extreme events

Weather  events are a major factor in annual crop yield variation. The projected impacts of climate change
often  consider changes in average temperature and precipitation patterns alone, while not reflecting the
potential  for altered variability in events such as droughts and floods.  The potential for these events to
change in frequency and magnitude introduces a key uncertainty regarding future projections of changes
in agricultural and food production due to climate change.  On this issue, the IPCC (Easterling et al. 2007)
drew  the following conclusion: "Recent studies  indicate that climate change scenarios that include
increased frequency of heat  stress,  droughts and flooding  events reduce  crop yields and livestock
productivity beyond the impacts  due to changes  in  mean variables alone, creating the possibility for
surprises. Climate variability and change also modify the risks of fires, and pest and pathogen outbreaks,
with negative consequences for food, fiber and forestry (high confidence)." The adverse effects on crop
yields due to droughts and other extreme events may offset the beneficial direct effects of elevated CO2,
moderate temperature increases over the near term, and longer growing seasons.

Drought  events are already a frequent occurrence,  especially in the  western  U.S.   Vulnerability to
extended  drought is,  according to IPCC  (Field  et al.,  2007), increasing  across North America as
population growth  and economic development increase demands from  agricultural, municipal,  and
industrial uses, resulting in frequent over-allocation of water resources.  Though droughts  occur more
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frequently  and intensely in the western part of the  U.S., the east is not immune from droughts and
attendant reductions in water supply, changes in water quality and ecosystem function, and challenges in
allocation (Field et al., 2007).

Average annual precipitation is projected to decrease  in the southwestern U.S. but increase over the rest
of North America (Christensen et al., 2007).   Some studies project widespread increases in extreme
precipitation (Christensen et al., 2007), with greater risks of not only flooding from intense precipitation,
but also droughts from greater temporal  variability in precipitation.  Increased runoff due to intense
precipitation on crop fields and animal agriculture operations may result in an increased contribution of
sediments, nutrients, pathogens, and pesticides in surface waters (Kundzewicz et al., 2007).

One economic consequence of excessive rainfall is delayed spring planting, which jeopardizes profits for
farmers paid  a premium for early season  production of high value horticultural crops such as melon,
sweet corn, and tomatoes (Hatfield et al.,  2008). Field flooding during the growing season causes crop
losses associated with anoxia, increases susceptibility to root diseases, increases  soil compaction (due to
use of heavy  farm equipment on wet soils), and causes more runoff and leaching  of nutrients and
agricultural chemicals into groundwater and surface water (Hatfield et al., 2008).

9(d)    Pests and weeds

Pests  and weeds  can reduce crop yields,  cause economic losses to farmers, and require  management
control  options.   How climate  change (elevated CO2,  increased temperatures, altered  precipitation
patterns, and changes in the frequency and  intensity of extreme events) may affect the prevalence of pests
and weeds is an issue of concern for food production  and the agricultural sector.  Recent warming trends
in the U.S. have led to earlier insect spring activity and proliferation of some species (Easterling, et al.,
2007).

The growth of many crops and  weeds is  being stimulated (Backlund et al.,  2008a). Weeds generally
respond more  positively  to increasing CO2 than most cash crops,  particularly C3 invasive weeds; and
while there are many weed species that have the C4 photosynthetic pathway and therefore show a smaller
response to atmospheric CO2 relative to C3 crops, in most agronomic situations, crops are in competition
with both C3 and C4 weeds (Backlund et al.,, 2008a).  The IPCC (Easterling et al., 2007) concluded, with
high confidence,  that climate variability and change modify the risks of fires,  and pest and pathogen
outbreaks, with negative consequences for food, fiber and forestry across all world regions.

Climate change is likely to lead to a northern migration of weeds (Backlund et al,  2008a). Recent research
also suggests that glyphosate, the most widely used  herbicide in the U.S., loses its efficacy on weeds
grown at the increased CO2  levels likely in the coming decades (Backlund et al., 2008a).

Disease pressure  on crops  and domestic animals will likely increase with earlier springs and warmer
winters, which will allow proliferation and higher survival rates of pathogens  and parasites. Regional
variation in warming and changes in rainfall  will also  affect the  spatial and temporal distribution of
diseases (Backlund et al., 2008a).

Most  studies,  however, continue  to investigate pest  damage as  a separate function of either elevated
ambient CO2 concentrations or temperature. Pests and weeds are additional factors that, for example, are
often omitted when projecting the direct stimulatory effect of elevated CO2 on crop yields.  Research on
the  combined effects of elevated CO2 and climate change on pests, weeds and disease is still insufficient
for U.S. and world agriculture (Easterling et al., 2007).
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9(e)    Livestock

Hatfield et al. (2008) describe how temperature changes and environmental stresses can result in declines
in physical activity and an associated  decline in eating and grazing activity (for ruminants and other
herbivores), or elicit a panting or shivering response, which increases maintenance requirements of the
animal and contributes to decreases in animal productivity.

Climate change has the potential to influence livestock productivity in a number of ways.  Elevated CO2
concentrations can affect forage quality; thermal stress can directly affect the health of livestock animals;
an increase in the frequency or magnitude of extreme  events can lead to livestock loss; and climate
change may affect the spread of animal diseases.  The IPCC has generated a number of new conclusions
in this area compared to the Third Assessment  Report  in 2001.  These  conclusions (Easterling et al.,
2007), along with those from the more recent CCSP report (Hatfield et al., 2008) include:

    •  Higher temperatures will very likely reduce livestock production during the summer season, but
       these losses will very likely be partially offset by warmer temperatures during the winter season.
       For ruminants, current management systems generally do not provide shelter to buffer the adverse
       effects of a changing climate;  such protection is more frequently available for non-ruminants
       (e.g., swine and poultry).

    •  Based on expected  vegetation changes  and  known environmental  effects  on forage  protein,
       carbohydrate, and fiber contents, both positive and negative changes in forage quality are possible
       as a result of atmospheric and climatic change. Elevated CO2 can increase the carbon to nitrogen
       ratio in forages and thus reduce the nutritional value of those grasses, which in turn affects animal
       weight and performance. Under elevated CO2, a decrease of C4 grasses and  an increase of C3
       grasses (depending upon the plant species that remain) may occur which could potentially reduce
       or alter the nutritional quality of the forage grasses available to grazing livestock; however the
       exact effects on both types of grasses and  their nutritional quality still needs to be determined.

    •  Increased climate variability (including extremes in both heat and cold) and droughts may lead to
       livestock loss. The impact on animal productivity due to increased variability in weather patterns
       will likely be far greater than effects associated with the average change in climatic conditions.

9(f)    Freshwater and marine fisheries

Freshwater fisheries are sensitive to changes in temperature and water supply, which affect flows of rivers
and streams, as well as lake levels.  Climate change can interact with other factors that affect the health of
fish and productivity of fisheries (e.g., habitat loss, land-use change).

The  IPCC (Field et al., 2007 and references therein) reviewed a number of North American studies
showing how freshwater fish are sensitive to, or are being affected by, observed changes in climate:

•   Cold- and cool-water fisheries, especially salmonids, have been declining as warmer/drier conditions
    reduce their habitat.  The sea-run  salmon  stocks are in steep decline  throughout much of North
    America;
•   Pacific salmon have been appearing in Arctic  rivers;39
•   Salmonid species have been affected by warming in U.S. streams;
39 Arctic includes large regions of Alaska, and the Alaskan indigenous population makes up largest indigenous
population of the Arctic (see ACIA, 2004).
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•   Success of adult spawning and survival of fry brook trout is closely linked to cold groundwater seeps,
    which  provide  preferred temperature  refuges  for  lake-dwelling populations.  Rates of fish egg
    development and mortality increase with temperature rise within species-specific tolerance ranges.

Regarding  the  impacts  of future climate change,  IPCC  concluded,  with high confidence for North
America, that cold-water fisheries will likely be negatively affected; warm-water fisheries will generally
benefit; and the results for cool-water fisheries will be mixed, with gains in the northern and losses in the
southern portions of ranges (Field et al., 2007).  A number of specific impacts by fish species and region
in North America are projected (Field et al., 2007 and references therein):

•   Salmonids, which prefer cold water, are likely to experience the most negative impacts;
•   Arctic freshwaters will likely be most affected, as they will experience the greatest warming;
•   Many warm-water and cool-water species will shift their ranges northward or to higher altitudes;
•   In the continental U.S., cold-water species will likely disappear from all but the deeper lakes, cool-
    water species will be lost mainly from shallow lakes, and warm water species will thrive except in the
    far south, where temperatures in shallow lakes will exceed survival thresholds.

Climate variability and change  can also impact fisheries in coastal and estuarine waters, although non-
climatic factors, such as  overfishing and habitat loss and degradation, are already responsible for reducing
fish stocks (Nichols et al., 2007).  Coral reefs, for example, are vulnerable to a range of stresses and for
many reefs, thermal  stress thresholds will be crossed, resulting  in bleaching, with  severe  adverse
consequences for reef-based fisheries (Nichols et al., 2007).  Increased storm intensity, temperature and
salt water intrusion in coastal water bodies can also adversely impact coastal fisheries production.
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Section 10

Forestry

This section addresses how climate change may affect forestry, including timber yields, wildfires and
drought risk, forest composition, and pests in the U.S.

The CCSP report addressing forestry and land resources (Ryan et al., 2008) made the following general
conclusions for the U.S.:

•   Climate change has very likely increased the size and number of forest fires, insect outbreaks, and
    tree mortality in the interior west, the Southwest, and Alaska, and will continue to do so. An increased
    frequency of disturbance is at least as important to ecosystem function as incremental changes in
    temperature, precipitation, atmospheric CO2, nitrogen deposition, and ozone pollution. Disturbances
    partially or completely change forest ecosystem structure and species composition, cause short-term
    productivity  and carbon storage loss, allow better opportunities for invasive alien species to become
    established, and command more public and management attention and resources.

For North America, the IPCC (Field et al., 2007) concluded:

•   Overall forest growth in  North  America will  likely increase modestly (10-20%)  as  a result of
    extended growing seasons and elevated CO2 over the next century, but with important spatial and
    temporal variation (medium confidence).40

•   Disturbances like wildfire and insect outbreaks are increasing and are likely to intensify in a warmer
    future with drier soils and longer growing seasons (very high confidence).  Although recent climate
    trends  have  increased  vegetation growth,  continuing increases in  disturbances are  likely to limit
    carbon storage, facilitate  invasive species, and disrupt ecosystem services.   Over the 21st century,
    pressure for species to shift north and to higher elevations  will  fundamentally rearrange  North
    American ecosystems. Differential capacities for range  shifts and constraints from development,
    habitat fragmentation,  invasive species, and  broken ecological connections will alter ecosystem
    structure, function, and services.

10(a)   Forest Productivity

Forestry productivity is known to be sensitive to changes in climate  variables (e.g. temperature, radiation,
precipitation, water vapor pressure in the air, and wind  speed), as these affect a  number of physical,
chemical, and biological processes in forest systems (Easterling, et al., 2007).  However, as noted in a
CCSP report addressing the forest sector (Ryan et al., 2008), it is difficult to separate the role of climate
from other potentially influencing factors, particularly because these interactions vary by location.

For the U.S.  as  a whole, forest growth and productivity have been observed to change, in part due to
observed climate change. Nitrogen deposition and warmer temperatures have very likely increased forest
growth  where water is not limiting (Ryan et al., 2008).  The IPCC (Field et al.,  2007  and references
therein) outlines a number of studies demonstrating the observed  connection between changes in U.S.
forest growth and changes in climate variables:
40 According to IPCC terminology, "medium confidence" conveys a 5 out of 10 chance of being correct. See Box
1.3 on page 5 for a full description of IPCC's uncertainty terms.
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•   Forest growth appears to be  slowly accelerating  (less than  1% per decade) in regions where tree
    growth has historically been limited by low temperatures and short growing seasons;
•   The length of the vegetation  growing season has increased an average of 2 days per decade since
    1950 in the conterminous U.S., with most of the increase resulting from earlier spring warming;
•   Growth is slowing in areas subject to drought;
•   On dry south-facing slopes in Alaska, growth of white spruce has decreased over the last 90 years,
    due to increased drought stress;
•   In semi-arid forests of the south-western U.S., growth rates have decreased since  1895, correlated
    with drought from warming temperatures;
•   Mountain forests are  increasingly encroached upon from  adjacent lowlands, while simultaneously
    losing high altitude habitats due to warming (Fischlin et al., 2007).
•   In Colorado,  aspen have advanced into the more cold-tolerant spruce-fir forests over the past 100
    years;
•   A combination of warmer  temperatures and  insect  infestations  has resulted in economically
    significant losses of forest resource base to spruce bark beetle in Alaska.

Forest productivity gains may result through: (i)  the direct stimulatory CO2 fertilization effect (although
the magnitude of this effect remains uncertain over the long term and can be curtailed by other changing
factors);  (ii)  warming  in  cold  climates,  given concomitant precipitation  increases to compensate for
possibly increasing water vapor pressure  deficits; and (iii) precipitation increases under water limited
conditions (Fischlin et al.,  2007).

New  studies  suggest that direct  CO2 effects on tree growth  may  be lower than previously assumed
(Easterling et al., 2007).   Additionally, the initial  increase in growth  increments  may  be limited by
competition,  disturbance,  air pollutants  (primarily tropospheric ozone), nutrient limitations, ecological
processes, and other factors, and the response  is site- and species-specific (Easterling et al.,  2007).
Similarly,  Ryan  et al. (2008) stated that, where  nutrients  are not limiting, rising  CO2 increases
photosynthesis and wood production (with younger stands responding most strongly), but that on infertile
soils the extra carbon from increased photosynthesis will be quickly respired.

The general findings from a number of recent syntheses using data from the  three American and one
European  CO2-enrichment FACE  study sites show that North American forests will absorb more CO2 and
might retain more carbon as atmospheric CO2 increases.  The increase in the rate of carbon sequestration
will be highest (mostly in wood)  on nutrient-rich soils with  no water limitation and will decrease with
decreasing fertility and water supply. Several yet unresolved questions prevent a definitive assessment of
the effect of  elevated CO2 on other components of the carbon cycle in forest  ecosystems (Ryan et al.,
2008).

As with  crop yields, ozone pollution will modify the effects  of  elevated CO2 and  any  changes  in
temperature and precipitation, but these multiple interactions are  difficult to predict because they have
been poorly studied (Ryan et al., 2008).  Nitrogen deposition also plays a role.  Nitrogen deposition and
warmer temperatures  have very  likely increased forest growth where  water  is not limiting and will
continue to do so in the near future. Nitrogen deposition has  likely increased forest growth rates over
large  areas, and interacts  positively to enhance the  forest growth  response to increasing CO2. These
effects are expected to continue in the future as N deposition and rising CO2 continue.

For the projected temperature increases over the next few decades, most studies  support the conclusion
that a modest warming of a few  degrees Celsius will lead to greater tree growth in the U.S. There are
many causes  for this enhancement including direct physiological  CO2 effects, a longer growing season,
and potentially greater mineralization of soil nutrients. Because different species may respond somewhat
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differently to warming, the competitive balance of species in forests may change. Trees will probably
become established in formerly colder habitats (more northerly, higher altitude) than at present (Ryan et
al., 2008).

Productivity gains in one area can occur simultaneously with productivity losses in other areas. For a
widespread species like lodgepole pine, a 3°C temperature increase would increase growth in the northern
part  of its range,  decrease growth  in the middle, and decimate southern forests  (Field et  al., 2007).
Climate change is expected to increase California timber production by the 2020s because of stimulated
growth in the standing forest.  In the long run (up  to 2100), these productivity gains were offset by
reductions in productive area for softwoods growth.   Risks of losses from Southern pine beetle likely
depend on the seasonality of warming, with winter and spring warming leading to the greatest  damage
(Easterling et al., 2007 and references therein).

According to studies reviewed by IPCC (Field et al., 2007), the effects of climate change,  in the  absence
of dramatic increases in disturbance, on the potential for commercial harvest in the 2040s ranged from
mixed for a low emissions scenario to positive for a high  emissions scenario. The tendency for North
American producers to  suffer losses increases if climate change is accompanied by increased disturbance,
with simulated losses averaging US$1-2 billion/year over the 21st century according to a 2005 study
referenced in Field et al. (2007).

U.S. forestry, in addition to  experiencing direct climate change effects, may be indirectly affected by
changing  forest productivity in different regions of the world.  Easterling et  al. (2007) cite  a study
showing two climate change  scenarios where North American forests undergo more dieback in  general
than forests in other regions of the world, and where certain North American forest yields increase but
less so compared to other regions. The implication is that forests in other parts of the world (including
tropical forests with shorter  rotations) could have a  competitive advantage within the global  forestry
sector under a changing climate.

Climate change will also substantially impact other non-timber goods and services, such as seeds, nuts,
hunting, resins, plants used in pharmaceutical and botanical  medicine, and in the cosmetics industry; these
impacts will vary  significantly across world regions (Easterling et  al., 2007).

10(b)   Wildfire and Drought Risk

While in some cases a changing climate may have positive  impacts  on the productivity of forest systems,
changes in disturbance patterns are expected to have a substantial impact on overall gains or losses. More
prevalent  forest fire disturbances have recently  been observed in the U.S. and  other  world  regions
(Fischlin,  et al., 2007).  Wildfires and droughts, among other extreme events (e.g., hurricanes) that can
cause forest damage, pose the largest threats over time to forest ecosystems.

Several lines of evidence suggest that large, stand-replacing wildfires will likely increase in frequency
over the next several decades because of climate warming (Ryan  et  al., 2008). General climate warming
encourages wildfires by extending the summer period  that dries fuels, promoting easier ignition and faster
spread (Field et al., 2007).

The IPCC (Field et al.,  2007 and references therein) noted a number of observed changes to U.S.  wildfire
size and frequency, often associating these changes with changes in average temperatures:

•   Since 1980, an average of about 22,000 km2/year (13,700 mi2/year) has burned in wildfires, almost
   twice the 1920-1980 average of about 13,000 km2/year (8,080 midyear);
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•   The forested area burned in the western U.S. from  1987-2003 is 6.7 times the area burned from 1970-
    1986;
•   Human vulnerability to wildfires  has increased, with a  rising population  in  the  wildland-urban
    interface;
•   In the last three decades, the wildfire season in the western U.S. has increased by 78 days, and burn
    durations  of fires greater than 1,000 ha (2,470 acres) have increased from 7.5 to 37.1 days, in
    response to a spring/summer warming of 0.87°C (1.4°F);
•   Earlier  spring snowmelt has  led  to  longer  growing  seasons and  drought, especially  at  higher
    elevations, where the increase in wildfire activity has been greatest;
•   In the south-western U.S., fire  activity is correlated with  El  Nino-Southern Oscillation (ENSO)
    positive phases and higher Palmer Drought Severity Indices.41  Major fire years tend to follow the
    switching  from El Nino to La Nina conditions due to buildup of material during wet years followed
    by desiccation during a dry year, whereas small fires are strongly associated directly with previous
    year drought.   Furthermore,  increased temperature in the  future will likely extend  fire seasons
    throughout the western United States,  with more fires  occurring earlier and later than is currently
    typical, and will increase the total area burned in some regions.

Though fires and extreme events are not well represented in models, current climate modeling  studies
suggest that increased temperatures and longer growing  seasons will elevate fire risk in connection with
increased aridity.  Some research identifies the possibility of a 10% increase in the seasonal severity of
fire hazard over much of the U.S. under climate  change (Easterling, et al.,  2007).  For Arctic regions,
forest fires are expected to  increase in  frequency and intensity (ACIA, 2004).  In California, the  risk of
increased wildfires as a result  of climate change has been identified as a significant issue (California
Energy Commission, 2006).

10(c)   Forest Composition

Climate change and associated changes in disturbance regimes will cause shifts in the distributions of tree
species and alter forest species composition.  With warming, forests will extend further north  and to
higher elevations.   Over currently dry regions, increased  precipitation may allow forests to displace
grasslands and savannas. Changes  in forest composition in turn can alter the frequencies, intensities, and
impacts of disturbances such as fire, insect outbreaks, and disease.

In Alaska and neighboring Arctic regions, there is strong evidence of recent vegetation  composition
change, as outlined by the IPCC (Anisimov et al., 2007 and references therein):

•   Aerial photographs show increased  shrub abundance  in 70% of 200 locations;
•   Along the Arctic to sub-Arctic  boundary, the tree-line has moved about 6 mi (10 km) northwards and
    2% of Alaskan tundra on the Seward Peninsula has been displaced by forest in the past 50 years;
•   The  pattern of northward and  upward tree-line advances  is  comparable  with  earlier Holocene
    changes;
•   Analyses of satellite images indicate that the  length of growing season is increasing by 3 days per
    decade in Alaska.

Likely rates of migration northward and to higher elevations are uncertain and depend not only on climate
change  but also  on future land-use patterns and  habitat fragmentation,  which can impede  species
41 The Palmer Drought Severity Index is used by NOAA and uses a formula that includes temperature and rainfall to
determine dryness.  It is most effective in determining long-term drought. Positive PDSI indicates wet conditions,
negative PDSI indicates dry conditions.
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migration.  Bioclimate modeling based on outputs from five general circulation models suggests increases
in tree species richness in the Northwest and decreases in the Southwest on long time scales (millennia).
Over the  next century,  however, even  positive long-term species richness may lead to short-term
decreases  because species that are intolerant of local conditions may disappear relatively quickly while
migration  of new species into the area may be quite slow (Field, et al., 2007; Currie 2001). The Arctic
Climate Impact Assessment (2004) also concluded  that vegetation zones  are  projected to migrate
northward, with forests encroaching on tundra and tundra encroaching on polar deserts. Limitations in
amount and quality of soils are likely to hinder these poleward shifts. No experiments have assessed the
effect of changes in precipitation on forest tree species composition (Ryan et al., 2008).

10(d)  Insects and Diseases

Insects and diseases are a natural  part of forested ecosystems and outbreaks often have  complex causes.
The  effects of insects and diseases can vary from defoliation and retarded growth, to timber damage, to
massive forest  diebacks. Insect life cycles can be  a factor in pest outbreaks; and insect lifecycles are
sensitive to climate  change.  Many northern insects have a two-year life-cycle, and warmer winter
temperatures allow a larger fraction of overwintering larvae to  survive.  Recently, spruce budworm in
Alaska has completed its life cycle in one year, rather than the previously observed duration of two years
(Field et al., 2007). Recent warming trends in the U.S. have led to earlier spring activity of insects and
proliferation of some species, such as the mountain pine beetle (Easterling  et al.,  2007).  During the
1990s, Alaska's Kenai Peninsula experienced an outbreak of spruce bark beetle over 16,000 km2 with 10-
20% tree mortality (Anisimov et al., 2007). Also following recent warming in Alaska, spruce budworm
has reproduced farther north reaching problematic numbers (Anisimov et al., 2007).  Climate change  may
indirectly  affect insect outbreaks by affecting the overall health and  productivity of trees.  For example,
susceptibility of trees to insects  is increased when multi-year droughts degrade  the  trees' ability to
generate defensive chemicals (Field, et al., 2007).   Warmer temperatures  have already enhanced the
opportunities for insect spread across the landscape in the U.S. and other world regions (Easterling et al.,
2007).

The  IPCC (Easterling et al., 2007) stated that modeling of future climate change impacts on insect and
pathogen  outbreaks  remains limited.   Nevertheless,  the IPCC  (Field et al., 2007) states with high
confidence that, across North America, impacts of climate change on commercial forestry potential are
likely to be sensitive to changes in disturbances from insects and diseases, as well as wildfires.

The  CCSP report (Ryan et al., 2008) states that the ranges of the mountain pine beetle and southern  pine
beetle  are  projected to  expand  northward as a result of average temperature  increases. Increased
probability of spruce beetle outbreak as  well  as increase in climate  suitability for mountain pine beetle
attack in high-elevation ecosystems has also been projected in response to warming (Ryan et al., 2008).

Climate change can shift the current boundaries of insects and pathogens and modify tree physiology and
tree  defense.  An increase in  climate extremes may also promote plant disease and pest outbreaks
(Easterling etal, 2007).
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Section 11

Water Resources

This section covers climate change effects on U.S. water supply, water quality, extreme events affecting
water resources, and water uses.  Information about observed trends as well as projected impacts is
provided.

The vulnerability of freshwater resources in the  U.S. to climate change varies from region to region.
Although water management practices in the U.S. are generally advanced, particularly in the West, the
reliance on past conditions as the basis for current and future planning will no longer be  appropriate, as
climate change increasingly creates conditions well outside of historical observations (Lettenmaier et al.,
2008).  Examples of large U.S. water bodies where climate change raises a concern include the  Great
Lakes, Chesapeake Bay, Gulf of Mexico, and the Columbia River Basin.

For North America, IPCC (Field et al., 2007) concluded:

•  Climate  change  will  constrain  North America's over-allocated  water  resources,  increasing
   competition among agricultural, municipal,  industrial, and ecological uses (very high  confidence)42  .
   Fusing temperatures will diminish snowpack and increase evaporation, affecting seasonal availability
   of water.  Higher demand from economic development, agriculture and population growth will further
   limit surface and groundwater availability.  In the Great Lakes and major river systems, lower  levels
   are  likely to  exacerbate challenges relating  to water quality, navigation, recreation,  hydropower
   generation, water transfers, and bi-national relationships.

ll(a)  Water Supply and Snowpack

Surface Water and Snow pack

The  semi-humid  conditions of the  eastern  U.S. transition to  drier conditions in the  west that are
interrupted by the Rocky Mountains.  The driest climates, however, exist in the Intermountain West and
Southwest, becoming more humid as  one proceeds west and north to more humid conditions on the
upslope areas of the  Cascade and coastal mountain ranges, especially  in the Pacific Northwest
(Lettenmaier et al., 2008).

IPCC reviewed a number of studies showing trends in U.S. precipitation patterns, surface water supply,
and snowpack, and how climate change may be contributing to some of these trends (Field  et al., 2007):

•  Annual precipitation has increased throughout most of North America.
•  Streamflow in the eastern U.S. has increased 25% in the last 60 years, but has decreased  by about 2%
   per decade in the  central Rocky Mountain region over the last century.
•  Since 1950, stream discharge in both the Colorado and Columbia river basins has decreased.
•  In regions with winter snow, warming has  shifted the magnitude and timing of hydrologic events.
   The fraction of annual precipitation falling as rain (rather than snow) increased at 74% of the weather
   stations studied in the western mountains of the U.S. from 1949-2004.
•  Spring and summer snow cover has also decreased in the U.S. West.
42 According to IPCC terminology, "very high confidence" conveys a 9 out of 10 chance of being correct.  See Box
1.3 on page 5 for a full description of IPCC's uncertainty terms.
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•   Break-up of river and lake ice across North America advanced by 0.2 - 12.9 days over the last 100
    years.

In the Arctic, precipitation has increased by about 8% on average over the past century. Much of the
increase has fallen as rain, with the largest increases occurring in autumn and winter. Later freeze-up and
earlier break-up  of river and lake ice have combined to reduce the ice season by one to three weeks in
some areas.  Glaciers throughout North America are melting, and the particularly rapid retreat of Alaskan
glaciers represents about half of the estimated loss of glacial mass worldwide (ACIA, 2004).  Permafrost
plays a large role in the hydrology of lakes and ponds.  The spatial pattern of lake disappearance strongly
suggests that permafrost thawing is driving the changes. These changes to Arctic precipitation, ice extent,
and glacial abundance will affect key regional bio-physical systems, act as climatic feedbacks (primarily
by changing surface albedo), and have  socio-economic impacts (high confidence) (Anisimov et al., 2007).

In regions  including the  Colorado  River, Columbia River,  and  Ogallala Aquifer,  surface and/or
groundwater resources are intensively used and  subject to competition from agricultural, municipal,
industrial, and ecological needs.  This increases the potential vulnerability to future changes in timing and
availability of water (Field et al., 2007).

Projections for the western mountains of the U.S. suggest that warming, and changes in the form, timing,
and amount of precipitation will very likely (high  confidence) lead to earlier melting and  significant
reductions in snowpack by the middle of the 21st century (Lettenmaier et al., 2008; Field  et al., 2007). In
mountainous snowmelt-dominated watersheds, projections suggest advances in the timing of snowmelt
runoff, increases in winter and early spring flows (raising flooding potential), and substantially decreased
summer flows.  Heavily-utilized water systems of the western U.S.  that rely  on capturing snowmelt
runoff, such as the Columbia River system, will be  especially vulnerable (Field et al., 2007).  Reduced
snowpack has been identified  as a  major concern  for  the  State  of California (California Energy
Commission, 2006).

Globally, current water management practices are very likely to be inadequate to reduce the negative
impacts of climate  change on water supply reliability, flood risk, and aquatic ecosystems (very high
confidence)  (Kundzewicz et al., 2007). Less reliable supplies of water are likely to create challenges for
managing urban water systems as well as for  industries that depend on large volumes  of water.  U.S.
water managers currently anticipate local, regional, or state-wide water shortages over the next ten years.
Threats to reliable supply are complicated by high population growth rates in western states where many
resources are at  or approaching full utilization.  In Eastern North America, daily precipitation so heavy
that it now occurs only once every 20  years is projected to occur approximately every eight years by the
end of this century, under a mid-range emission scenario (CCSP, 2008i).  Potential increases in heavy
precipitation, with expanding impervious surfaces, could increase urban flood risks and create additional
design challenges and costs for storm water management (Field et al., 2007). The IPCC (Field et al.,  2007
and references therein) reviewed several regional-level studies on  climate change impacts to U.S. water
management which showed:

•   In the Great Lakes - St. Lawrence Basin,  many, but not all, assessments project  lower net basin
    supplies and lake water levels. Lower water levels are likely to influence many sectors, with multiple,
    interacting  impacts (IPCC: high  confidence).    Atmosphere-lake interactions  contribute to the
    uncertainty in assessing these impacts though.
•   Urban water supply systems in North America often draw water from  considerable distances, so
    climate impacts need not be local to affect cities. By the 2020s, 41% of the water supply to southern
    California is likely to be vulnerable due to  snowpack loss in the Sierra Nevadas and Colorado River
    basin.
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•   The New York area will likely experience greater water supply variability. New York City's system
    can likely adapt to future changes, but the region's smaller systems may be vulnerable, leading to a
    need for enhanced regional water distribution plans.

In the Arctic, river discharge to the ocean has  increased during the past few decades, and peak flows in
the spring are occurring earlier.  These changes are projected to accelerate with  future climate change.
Snow cover extent in Alaska is projected to decrease by 10-20% by the 2070s, with greatest declines in
spring (ACIA, 2004 and reference therein).

The IPCC concluded with high confidence that under most climate change scenarios,  water resources in
small islands around the globe are likely to be seriously compromised (Mimura et al., 2007).  Most small
islands have  a limited water supply, and water resources in these islands  are especially vulnerable to
future changes and distribution of rainfall.  Reduced rainfall typically leads to decreased surface water
supply and slower recharge rates of the freshwater lens43, which can result in prolonged drought impacts.
Many islands in the Caribbean (which include U.S. territories of Puerto Rico and U.S. Virgin Islands) are
likely to experience  increased water stress as a result of climate change.  Under all SRES scenarios,
reduced rainfall in summer is projected for the Caribbean, making it unlikely that the demand for water
resources will be met.  Increased rainfall  in winter is unlikely to compensate for these water deficits due
to lack of storage capacity (Mimura et al.,  2007).

Groundwater

Groundwater systems generally respond  more slowly to  climate change than  surface water  systems.
Limited data on existing supplies of groundwater makes it difficult to understand and measure climate
effects.   In general, groundwater levels correlate  most  strongly  with precipitation, but temperature
becomes more important for shallow aquifers, especially  during warm periods.  In semi-arid  and arid
areas, groundwater resources are particularly vulnerable because  precipitation and  streamflow  are
concentrated over a few months, year-to-year variability is high, and deep groundwater wells or reservoirs
generally do not exist (Kundzewicz et al.,  2007).

With climate change, availability of groundwater is likely to be influenced by changes in withdrawals
(reflecting  development,  demand,  and   availability  of other  sources)  and  recharge (determined by
temperature, timing,  and amount of precipitation, and surface water interactions) (medium confidence).
In general, simulated aquifer levels respond to changes in temperature, precipitation, and the level of
withdrawal. According to IPCC, base flows were found to decrease in scenarios that are drier or have
higher pumping rates, and increase in wetter scenarios on  average across world regions (Kundzewicz et
al., 2007).

Projections suggest that efforts to offset  declining surface water availability by increasing groundwater
withdrawals will be hampered by decreases in groundwater recharge in some water-stressed regions, such
as the  southwest  US.  Vulnerability in these  areas is  also often exacerbated by the rapid increase of
population and water demand (high confidence) (Kundzewicz et al., 2007).  Projections for the  Ogallala
aquifer region suggest that natural groundwater recharge decreases more than 20% in all simulations with
different climate  models  and future warming scenarios  of 2.5°C  or  greater (Field et al., 2007 and
reference therein).
43 Freshwater lens is defined as a relatively thin layer of freshwater within island aquifer systems that floats on an
underlying mass of denser seawater. Numerous factors control the shape and thickness of the lens, including the
rate of recharge from precipitation, island geometry, and geologic features such as the permeability of soil layers.
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In addition, sea level rise will extend areas of salinization of groundwater and estuaries, resulting in a
decrease in freshwater availability for humans and ecosystems in coastal areas. For a discussion of these
impacts, please see Section 12.

ll(b)   Water Quality

The  IPCC concluded with  high confidence that higher water temperatures,  increased precipitation
intensity,  and  longer periods of low flows exacerbate many forms  of water pollution and  can impact
ecosystems, human health, and water system reliability and operating costs (Kundzewicz et al., 2007). A
CCSP  (2008e) report  also  acknowledges that water quality is  sensitive to both  increased  water
temperatures and changes in precipitation.

Pollutants of concern in this  case include sediment, nutrients, organic matter, pathogens, pesticides, salt,
and thermal pollution (Kundzewicz et al., 2007).  IPCC (Kundzewicz et al., 2007) reviewed several
studies discussing the impacts of climate change on water quality that showed:

•   In lakes and reservoirs, climate change effects are primarily caused by water temperature variations.
    These variations can be caused by climate change or indirectly through increases in thermal pollution
    as a result of higher demand for cooling water in the energy sector. This affects, for the U.S. and all
    world regions, dissolved oxygen regimes, redox potentials44, lake stratification, mixing rates, and the
    development of aquatic biota, as they all depend on water temperature. Increasing water temperature
    affects the self-purification capacity of rivers by reducing the amount  of dissolved oxygen available
    for biodegradation.

•   Water pollution problems are exacerbated during low flow conditions where small water quantities
    result in less dilution and greater concentrations of pollutants.

•   Heavy precipitation frequencies in  the U.S. were at a minimum in the  1920s and  1930s,  and have
    increased through the 1990s (Field,  et al., 2007).  Increases in  intense rain  events result in the
    introduction of more sediment,  nutrients, pathogens,  and toxics into  water bodies from non-point
    sources but these events also provide the pulse flow needed for some ecosystems.

North American simulations  of future surface and bottom  water temperatures of lakes, reservoirs, rivers,
and estuaries consistently increase, with summer surface temperatures exceeding 30°C in midwestern and
southern lakes and reservoirs.  IPCC projects that warming is likely to  extend and intensify summer
thermal stratification in surface waters, further contributing to  oxygen depletion (Field et al., 2007 and
references therein).

Higher water temperature and variations in runoff are likely to produce adverse changes in water quality
affecting human health, ecosystems, and water uses.  Elevated surface water temperatures will promote
algal blooms and  increases in bacteria  and fungi levels.   Increases in water temperature can also make
some contaminants, such  as ammonia (EPA, 1999), more toxic for some species and foster the growth of
microbial  pathogens in sources of drinking water. Warmer waters also transfer volatile and semi-volatile
compounds (ammonia, mercury, PCBs, dioxins,  pesticides) from surface water bodies to the  atmosphere
more rapidly (Kundzewicz et al., 2007). Although this transfer will improve water quality, this may have
implications for air quality.
 1 Redox potential is defined as the tendency of a chemical species to acquire electrons and therefore be reduced.
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Lowering of the water levels in  rivers and lakes  can lead to re-suspension of bottom sediments and
liberating compounds, with negative effects on water supplies (Field et al., 2007 and references therein).
These impacts may lead to a bad  odor  and taste in chlorinated drinking water and greater occurrence of
toxins.  More intense rainfall will  lead to increases  in suspended solids (turbidity) and pollutant levels in
water bodies due to soil erosion (Kundzewicz et al., 2007). Moreover, even with enhanced phosphorus
removal in wastewater treatment plants, algal growth in water bodies may increase with warming over the
long term.  Increasing nutrient and sediment loads due to more intense runoff events will negatively affect
water quality, requiring additional  treatment to render it suitable for drinking water.

Climate change is  likely to make it more difficult to  achieve existing water quality goals for sediment
(IPCC:  high confidence) because  hydrologic changes affect many  geomorphic processes including soil
erosion, slope stability, channel erosion, and sediment transport  (Field et al., 2007).  IPCC reviewed a
number of region-specific studies on U.S. water quality and projected that:

•   Changes in precipitation may increase nitrogen loads  from rivers  in the Chesapeake and Delaware
    Bay regions by up to 50% by 2030 (Kundzewicz et al., 2007 and reference therein).

•   Decreases in snowcover and  increases  in winter rain  on bare  soil will likely lengthen the erosion
    season and enhance erosion intensity.  This will increase the  potential  for sediment related water
    quality impacts in  agricultural areas without appropriate  soil management techniques (Field et al.,
    2007 and reference  therein).  All studies on soil erosion suggest that increased rainfall amounts and
    intensities will lead to greater  rates  of erosion, within the U.S. and in other regions, unless protection
    measures are taken (Kundzewicz et al., 2007).  Soil management practices (e.g., crop  residue, no-till)
    in  some regions (e.g., the  Cornbelt) may not provide sufficient  erosion protection against future
    intense precipitation and associated runoff (Field et al., 2007).

ll(c)   Extreme Events

There are a number of climatic  and non-climatic drivers influencing flood and drought impacts. Whether
risks are realized  depends on  several  factors.   Floods can be  caused by intense  and/or long-lasting
precipitation events, rapid snowmelt, dam failure, or reduced conveyance due to ice jams or landslides.
Flood magnitude and spatial extent depend on the  intensity, volume, and time of precipitation, and the
antecedent conditions of rivers and their drainage basins (e.g., presence of snow and ice, soil composition,
level of human development, existence of dikes, dams, and reservoirs, etc.) (Kundzewicz et al., 2007).

Precipitation intensity will increase across the U.S., but particularly  at mid and high latitudes where mean
precipitation also increases. This will affect the risk of flash flooding and urban flooding (Kundzewicz et
al., 2007).  Some studies project widespread increases in extreme precipitation with greater risks of not
only  flooding  from intense precipitation  but  also  droughts   from  greater temporal  variability in
precipitation.  In general, projected changes in precipitation extremes are larger than changes in mean
precipitation (Field et al., 2007).

The socio-economic impacts of droughts arise  from the interaction between climate, natural conditions,
and human factors such as changes in land use. In dry areas, excessive water withdrawals from surface
and groundwater sources can exacerbate the impacts  of drought (Kundzewicz et al., 2007).  Although
drought has been more frequent and intense in the western  part of the U.S., the East is also vulnerable to
droughts and attendant reductions  in water supply, changes in water quality and ecosystem function, and
challenges in allocation (Field et al., 2007).
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In addition to the effects on water supply, extreme events, such as floods and droughts, will likely reduce
water quality.  Increased erosion and runoff rates during flood events will wash pollutants (e.g., organic
matter, fertilizers, pesticides, heavy metals)  from soils into water bodies,  with subsequent impacts to
species and  ecosystems.  During drought events, the lack of precipitation and subsequent low flow
conditions will impair water quality by reducing the amount of water available to dilute pollutants. These
effects from floods  and droughts will make  it more difficult to achieve pollutant discharge limits and
water quality goals (Kundzewicz et al., 2007).

ll(d)  Implications for Water Uses

There are many competing water uses in the U.S. that will be  adversely impacted by climate change
impacts to water supply and quality.  The IPCC reviewed a number of studies describing  the impacts of
climate change on water uses in the U.S. which showed:

•   Decreased water supply  and lower water  levels  are  likely to exacerbate challenges  relating to
    navigation in the U.S. (Field et al., 2007).   Some studies have found that low flow conditions may
    restrict ship loading in shallow ports and harbors (Kundzewicz et al., 2007).  However, navigational
    benefits  from climate change exist as well.  For example, the navigation season for  the North Sea
    Route is projected to increase from the current 20-30 days per year to 90-100 days by 2080 (ACIA,
    2004 and references therein).
•   Climate  change  impacts to water supply  and quality will affect agricultural practices, including the
    increase of irrigation demand in dry regions and the aggravation of non-point source water pollution
    problems in areas susceptible to intense rainfall events and flooding (Field  et al., 2007).  For more
    information on climate change impacts to agriculture, please see Section 9.
•   The U.S. energy sector,  which relies  heavily on  water  for generation (hydropower) and cooling
    capacity, will be adversely impacted by changes to water supply and quality in reservoirs and other
    water bodies (Wilbanks et al., 2007). For more information on climate change impacts to the energy
    sector, please see Section  13.
•   Climate-induced environmental  changes (e.g.,  loss of glaciers, reduced river discharge in some
    regions,  reduced snow fall in winter) will affect park tourism, winter sport activities, inland water
    sports (e.g., fishing, rafting, boating), and other recreational uses dependent upon precipitation (Field
    et al., 2007).  While the North American tourism industry acknowledges the important influence of
    climate,  its impacts have not been analyzed comprehensively.
•   Ecological uses  of water could be adversely impacted by climate change. Temperature increases and
    changed precipitation  patterns  alter flow and flow timing.   These changes will threaten aquatic
    ecosystems (Kundzewicz et. al.,  2007).   For more  information, on  climate change impacts  on
    ecosystems and  wildlife, please see Section 14.
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Section  12

Sea Level Rise and Coastal Areas

This section of the document  discusses areas in the U.S.  vulnerable to  sea  level rise,  associated
interactions with coastal development, important coastal processes, observed and projected impacts, and
how climate change effects on extreme events will impact coastal areas. Information on the observed and
projected rates of sea level rise due to climate change can be found in Sections 4(g) and 6(c), respectively.
Information on ocean acidification is discussed in Sections 4(1), 6(b), and 14(a).

The IPCC (Field et al., 2007) concluded the following when considering how climate change may affect
sea level rise and coastal areas in North America:

•   Coastal communities and habitats will be increasingly stressed by climate change impacts interacting
    with development and pollution (very high confidence).45  Sea level is rising along much of the coast,
    and the rate of change will increase in the future, exacerbating the impacts of progressive inundation,
    storm-surge flooding, and shoreline erosion.
•   Storm impacts are likely  to be more severe, especially  along the  Gulf and Atlantic coasts.   Salt
    marshes, other coastal habitats,  and dependent species are threatened by  sea-level rise, fixed
    structures  blocking landward migration, and changes in vegetation.  Population growth  and rising
    value of infrastructure in coastal areas increases  vulnerability to climate variability and future climate
    change.

12(a)   Vulnerable Areas

Interaction with Coastal Zone Development

Coastal population growth in  deltas, barrier islands, and estuaries has led to widespread conversion of
natural  coastal landscapes to agriculture and aquaculture as well as  industrial and residential uses.
According  to  NOAA  (Crossett et al., 2007), approximately 153 million people  (53%  of the total
population)  lived in the 673 US coastal  counties46  in 2003.  This represents an increase of 33 million
people since 1980, and by 2008, the number was projected to rise  to 160 million. This population growth,
the rising value of coastal property, and  the projected increases in storm intensity  have increased the
vulnerability of coastal areas to climate variability and future climate change (IPCC, 2007b).

For small islands, the coastline is long relative to island area. As a result, many resources and  ecosystem
services are threatened by a combination  of human pressures and climate change effects including sea-
level rise, increases in sea surface temperature, and possible increases in extreme weather events (Mimura
et al., 2007).

Although climate change is impacting  coastal systems, non-climate human  impacts have been more
damaging over the past century.  The major non-climate impacts for the U.S. and  other world regions
include drainage  of coastal wetlands,  resource  extraction47, deforestation, introductions of invasive
species,  shoreline  protection,  and the discharge  of sewage, fertilizers,  and contaminants into  coastal
45 According to IPCC terminology, "very high confidence" conveys a 9 out of 10 chance of being correct.  See Box
1.3 on page 5 for a full description of IPCC's uncertainty terms.
46 "Coastal county" is generally defined in NOAA reports as a county in which at least 15 percent of its total land
area is located within a coastal watershed.
47 Resource extraction activities in coastal areas include sand/coral mining, hydrocarbon production, and commercial
and recreational fishing.
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waters (Nicholls  et  al.,  2007).   The cumulative  effect of these non-climate, anthropogenic  impacts
increases the vulnerability of coastal systems to climate-related stressors.

Coastal Processes

Climate change and sea-level rise affect sediment transport in complex ways.  Erosion and ecosystem loss
is affecting many parts of the US coastline, but it remains unclear to what extent these losses result from
climate change instead of land loss associated with relative sea-level rise due to subsidence and other
human drivers (Nicholls et al., 2007).

Coastal wetland loss is also being observed in the U.S. where these ecosystems are squeezed between
natural and artificial landward  boundaries  and rising  sea levels, a process known as  'coastal squeeze'
(Field et al., 2007).  The degradation of coastal ecosystems, especially wetlands and coral reefs, can have
serious implications for the well-being of societies dependent on them for goods and services (Nicholls et
al., 2007).  For more information regarding climate change impacts to coral reefs, see Section 14.

Engineering structures, such as bulkheads,  dams, levees, and water diversions, limit sediment supply to
coastal areas.  Wetlands are especially threatened by sea level rise when insufficient amounts of sediment
from upland watersheds are deposited on them.  If sea level rises slowly, the balance between sediment
supply and morphological adjustment can be maintained if a salt marsh vertically accretes48, or a lagoon
infills, at the same  rate.  However, an acceleration in the rate of sea-level  rise may mean that coastal
marshes and wetlands cannot keep up, particularly where the supply of sediment is  limited (e.g., where
coastal floodplains are inundated after natural levees or artificial embankments are overtopped) (Nicholls
et al., 2007).

Although  open coasts have been the focus of research on erosion and shore stabilization technology,
sheltered coastal areas in the U.S. are also vulnerable and suffer secondary effects from rising seas (NRC,
2006a). For example, barrier island erosion in Louisiana has increased the height of waves reaching the
shorelines  of  coastal bays.   This has enhanced erosion rates of beaches, tidal creeks,  and adjacent
wetlands.  The impacts of accelerated sea-level rise on gravel beaches have  received less attention than
sandy beaches; however these systems are threatened by sea-level rise, even under high wetland accretion
rates. The persistence of gravel and cobble-boulder beaches will  also be influenced by storms, tectonic
events, and other factors that build and reshape these highly dynamic shorelines (Nicholls et al., 2007).

Observed Changes

According to the IPCC, most of the world's sandy shorelines retreated during the past century and climate
change induced sea-level rise is one underlying cause.  Over the past century in the U.S., more than 50%
of the original salt marsh habitat has been lost.  In Mississippi  and Texas, over half of the shorelines
eroded at average rates of 2.6 to 3.1 m/yr since the 1970s, while 90% of the Louisiana shoreline eroded at
a rate of 12.0 m/yr (Nicholls et al., 2007 and references therein).

In the Great Lakes where  sea level rise is not  a  concern,  both  extremely  high and  low water levels
resulting from changes to the hydrological cycle have been damaging and disruptive to shoreline
communities (Nicholls et al., 2007).  High lake water levels increase  storm surge  flooding,  accelerate
shoreline erosion, and damage industrial and commercial infrastructure located on the shore. Conversely,
low lake water levels  can pose problems  for navigation, expose intake/discharge  pipes  for electrical
utilities and municipal water treatment plants, and cause unpleasant odors.
48 The term 'vertical accretion' is defined as the accumulation of sediments and other materials in a wetland habitat
that results in build-up of the land in a vertical direction.
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In the Arctic, coastal stability is affected by factors common to all areas (i.e., shoreline exposure, relative
sea level  change, climate, and local geology), and by  factors  specific to the  high-latitudes (i.e.,  low
temperatures,  ground ice, and sea ice) (Anisimov et al.,  2007).  Adverse  impacts  have already been
observed along Alaskan coasts and traditional knowledge points to widespread coastal change in Alaska.
Rising temperatures in Alaska are reducing the thickness and spatial extent of sea ice.  This creates more
open water and allows for winds to generate stronger waves, which increase shoreline erosion. Sea level
rise and thawing of coastal permafrost exacerbate this problem.  Higher waves will create even greater
potential for this kind of erosion damage (ACIA, 2004).

Projected Impacts

The U.S. coastline is long and diverse with a wide range of coastal characteristics.  Sea level rise  changes
the shape and location of coastlines by moving them landward along low-lying contours and exposing
new areas to  erosion (NRC,  2006a).  Coasts subsiding due to natural or human-induced causes  will
experience larger relative rises in sea level.  In some locations, such as deltas and coastal cities (e.g., the
Mississippi delta and surrounding cities), this effect can be significant (Nicholls et al.,  2007).  Rapid
development,  including an additional 25 million people  in the coastal U.S. over the next 25 years,  will
further reduce the resilience of coastal areas to rising sea levels (Field et al., 2007). Superimposed on the
impacts of erosion and subsidence, the  effects of rising  sea level will exacerbate  the  loss of waterfront
property and increase vulnerability to inundation hazards  (Nicholls et al., 2007).

If sea-level rise occurs over the next century  at a rate consistent with  the higher range of the  2007 IPCC
scenarios  (i.e., 50-60 cm rise  in sea level by 2100), it is about as likely as not that some barrier island
coasts  in the mid-Atlantic region will cross a geomorphic threshold and experience significant changes.
Such changes include more rapid landward  migration or barrier island segmentation (Gutierrez et al.,
2009).

Up to 21% of the remaining coastal wetlands  in the U.S.  mid-Atlantic region are potentially at risk of
inundation between 2000  and 2100 (Field et al., 2007 and reference  therein).  Rates of coastal  wetland
loss, in the Chesapeake Bay  and elsewhere, will increase with accelerated sea-level rise, in  part due to
'coastal squeeze'  (IPCC: high confidence).    It is  virtually  certain  that  those tidal wetlands already
experiencing submergence by sea-level rise and associated high rates of loss will continue to lose area in
the future due to both accelerated rates sea-level rise  as  well  as  changes in  other  environmental  and
climate drivers (Cahoon et al., 2009).   Salt-marsh biodiversity is likely to decrease in north-eastern
marshes through  expansion of non-native species such as Spartina alterniflora.  The  IPCC (Field  et al.,
2007) projects that many  U.S. salt marshes in less developed areas can potentially keep pace with  sea-
level rise through vertical accretion.

Climate  change  is  likely to  have a strong  impact on  saltwater  intrusion  into  coastal  sources of
groundwater in the U.S. and other  world regions.  Sea-level rise and high rates of water  withdrawal
promote the intrusion of saline water into the groundwater supplies, which adversely affects water quality.
Reduced  groundwater   recharge  associated  with   decreases   in  precipitation  and   increased
evapotranspiration49 will exacerbate  sea level rise effects on salinization rates (Kundzewicz et al., 2007).
This effect could impose enormous costs on water treatment infrastructure (i.e., costs associated with
relocating infrastructure  or building desalinization  capacity), especially  in densely  populated coastal
areas.  Saltwater intrusion is also projected to occur in freshwater bodies along the coast.  Estuarine and
49 Evapotranspiration is defined as the total amount of evaporation from surface water bodies (e.g., lakes, rivers,
reservoirs), soil, and plant transpiration.  In this context, warmer temperatures brought on by climate change will
drive greater levels of evapotranspiration.
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mangrove ecosystems can withstand a range of salinities on a short term basis; however, they are unlikely
to survive permanent exposure to high salinity environments. Saltwater intrusion into freshwater rivers
has already been linked with the decline of bald cypress forests in Louisiana and cabbage palm forests in
Florida.  Given that these ecosystems provide a variety of ecosystem services and goods (e.g., spawning
habitat for fish, pollutant filtration, sediment control, storm surge  attenuation), the loss of these  areas
could be significant (Kundzewicz et al., 2007).

The vulnerable nature of coastal indigenous communities to climate change arises from their geographical
location, reliance on the local environment for aspects of everyday life such as diet and economy, and the
current state of social, cultural, economic, and political change taking place in these regions  (Anisimov et
al., 2007).  Sea ice extent in the Arctic Ocean is expected to continue to decrease and may even disappear
entirely during summer months in the  coming decades.   This reduction of sea ice increases extreme
coastal erosion in  Arctic Alaska, due  to the increased exposure of the coastline to strong wave action
(CCSP, 2008i). These effects, along with sea level rise, will accelerate the  already high coastal erosion
rates in permafrost-rich areas of Alaska's coastline, thereby forcing  the issue of relocation for threatened
settlements. It has been estimated that relocating the village of Kivalina, AK to a nearby site would cost
US$54 million (Anisimov et al., 2007).

For small islands,  some  studies suggest that sea-level rise could reduce island size, particularly in the
Pacific, raising concerns for  Hawaii and other U.S.  territories  (Mimura et al., 2007).   In some cases,
accelerated coastal erosion may lead to island abandonment, as has  been documented in the Chesapeake
Bay.  Island infrastructure tends to predominate in coastal locations.  In the Caribbean and Pacific Islands,
more  than 50% of the population lives within 1.5 km of the shore.  International airports, roads, capital
cities, and other types of infrastructure are typically sited along  the coasts  of these  islands as  well.
Therefore, the socio-economic well-being of island communities will be threatened by inundation, storm
surge, erosion, and other  coastal hazards resulting from climate change (high confidence) (Mimura et al.,
2007).

12(b)  Extreme Events

Although increases in mean sea level  over the 21st century and beyond will inundate unprotected, low-
lying  areas, the most devastating impacts are likely to be associated with storm surge (Nicholls et al.,
2007). For example, the Maryland Geological Survey estimated that more than 20 acres of the State's
land was lost  on the western shore of Chesapeake Bay in the wake  of Tropical Storm Isabel, causing
approximately $84,000,000 in damages to shoreline structures (NRC, 2006a and references therein).

Superimposed on accelerated sea level rise, storm intensity, wave  height, and storm surge projections
suggest more  severe  coastal  flooding  and erosion hazards (Nicholls et al.,  2007).  Higher sea  level
provides an elevated base for storm surges to build upon and diminishes the rate at which low-lying  areas
drain, thereby increasing the  risk of flooding from rainstorms (CCSP, 2009b).  In  New York City and
Long  Island, flooding from a combination of sea  level rise and storm surge could be several meters deep
(Field et al., 2007). Projections suggest that the return period of a 100-year flood event in this area might
be reduced to  19-68 years, on average, by the 2050s, and to 4-60 years by the 2080s (Wilbanks et al.,
2007; and references therein).

Additionally, some major urban centers  in the U.S. are situated  in low-lying flood plains. For example,
areas  of New Orleans and its vicinity are 1.5-3 meters below sea level.  Considering the rate of subsidence
and using a mid-range estimate of 480 millimeters sea-level rise by 2100, it is projected that this region
could be 2.5 to 4.0 meters or more below mean sea level by 2100 (Field et al., 2007). In this scenario, a
storm surge from a Category 3 hurricane (estimated at 3 to 4 meters  without waves) could be six to seven
meters above areas that were heavily populated in 2004 (Field et al., 2007 and references therein).
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The IPCC discusses a number of other extreme  event scenarios and observations with implications for
coastal areas of the US (See also section 6(f) for a discussion of abrupt changes and sea level rise):

•   Very large sea-level rises that would result from widespread deglaciation of Greenland and West
    Antarctic ice sheets  imply major changes in  coastlines and ecosystems, and inundation of low-lying
    areas, with  greatest  effects  in  river  deltas.  Relocating  populations,  economic  activity, and
    infrastructure would be costly and challenging (IPCC, 2007b).
•   Under El  Nino conditions, high water levels  combined  with changes in winter  storms along the
    Pacific coast have produced severe coastal flooding and storm impacts.  In San Francisco, 140 years
    of tide-gauge data suggest an  increase in severe winter storms since  1950 and some studies have
    detected accelerated coastal erosion (Field et al., 2007).
•   Recent winters  with less ice in the Great Lakes and Gulf  of St. Lawrence  have  increased coastal
    exposure to damage  from winter storms (Field et al., 2007).
•   Recent severe tropical and extra-tropical storms demonstrate that North American urban centers with
    assumed high adaptive capacity remain vulnerable to extreme events (Field et al., 2007).

Demand for waterfront property and building land in  the U.S. continues to  grow,  increasing the value of
property at risk. Of the $19 trillion value of all insured residential  and commercial property in the US
states exposed to  North Atlantic  hurricanes,  $7.2 trillion  (41%) is located  in  coastal  counties50.
According to a study referenced in Field et al. (2007), this economic value  includes 79% of the property
in Florida, 63% of property  in New York, and  61% of the property in Connecticut.   The devastating
effects of hurricanes Ivan in 2004 and Katrina,  Rita and Wilma in 2005  illustrate the vulnerability of
North American infrastructure and urban systems that were not designed or not maintained to adequate
safety margins. When protective systems fail, impacts can be widespread and multi-dimensional (Field et
al., 2007).
50 "Coastal county" is generally defined in NOAA reports as a county in which at least 15 percent of its total land
area is located within a coastal watershed.
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Section 13

Energy, Infrastructure and Settlements

According to IPCC  (Wilbanks et al., 2007), "[industries, settlements and human society are accustomed
to variability in environmental conditions, and in many ways they have become resilient to it when it is a
part of their normal experience. Environmental changes that are more  extreme  or persistent than that
experience, however, can lead to vulnerabilities,  especially if the  changes are  not foreseen and/or if
capacities for adaptation are limited."

Climate change is likely51 to affect  U.S.  energy  use and energy production; physical  infrastructures;
institutional infrastructures; and will likely interact with and possibly exacerbate ongoing environmental
change and environmental pressures in settlements (Wilbanks et al., 2007), particularly in Alaska where
indigenous communities are facing major environmental and cultural impacts on their historic lifestyles
(ACIA, 2004).  The research evidence is relatively clear that climate warming will mean reductions in
total U.S. heating requirements and increases in total cooling requirements for buildings. These changes
will vary by region and by season, but they will affect household and business  energy  costs and their
demands on energy supply institutions. In general, the changes  imply increased demands for electricity,
which  supplies virtually all cooling energy services but only some heating services. Other effects  on
energy consumption are less clear (CCSP, 2007a).

13(a)  Heating and Cooling Requirements

With climate warming, less heating is required for industrial, commercial, and residential buildings in  the
U.S., but more cooling is required, with changes varying by region and by season. Net energy demand at
a national scale will be influenced by the structure of the energy supply. The main source of energy  for
cooling is electricity, while coal, oil, gas, biomass, and electricity are used for space heating.  Regions
with substantial requirements for both cooling and  heating could find that net annual electricity demands
increase while demands for other heating energy sources decline.  Critical factors for the U.S. are  the
relative efficiency of space cooling in summer compared to space heating in winter, and the  relative
distribution of populations in colder  northern or warmer southern regions.  Seasonal variation  in total
demand is also important. In some cases, due to infrastructure limitations, peak demand could go beyond
the  maximum capacity of the electricity transmission system (Wilbanks et al., 2007).

Recent North American studies generally confirm  earlier work  showing a small net change (increase or
decrease, depending on methods, scenarios, and location) in net demand for energy  in buildings but a
significant  increase  in demand for  electricity for space cooling,  with  further increases  caused  by
additional market penetration  of  air conditioning (high  confidence) (Field et  al., 2007).  Generally
speaking, the net effects of climate change in the U.S. on total energy demand are projected to amount to
between perhaps a 5% increase and decrease in demand per 1°C in warming in buildings. Existing studies
do not agree on whether there would be  a net increase or decrease in energy consumption with changed
climate because a variety of methodologies have been used (CCSP, 2007a).

In California,  if temperatures  rise according  to a high scenario range (8-10.5°F; ~4.5-5.6°C), annual
electricity demand for air conditioning could increase by as much as  20% by the end of the  century
(assuming population remains unchanged and limited implementation of efficiency measures) (California
51 According to IPCC terminology, "likely" conveys a 66 to 90% probability of occurrence.  See Box 1.3 on page 5
for a full description of IPCC's uncertainty terms.
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Energy Commission, 2006)52. In Alaska, there will be savings on heating costs: modeling has predicted a
15% decline in the demand for heating energy in the populated parts of the Arctic and sub-Arctic and up
to one month decrease in the duration of a period when heating is needed (Anisimov et al, 2007).

Overall, both net delivered energy and net primary energy consumption increase or decrease only a few
percent with  a 1°C or 2°C warming; however, there is a robust result that, in the absence of an energy
efficiency policy directed at space  cooling, climate  change would cause a significant  increase  in the
demand for electricity in the U.S., which would require the building of additional electricity generation
capacity (and probably transmission  facilities) worth many billions of dollars (CCSP, 2007a).

Beyond the general changes described above, general temperature increases can mean changes  in energy
consumption  in  key climate-sensitive  sectors of the economy, such as transportation, construction,
agriculture, and others.  Furthermore, there may be increases in energy used to supply other resources for
climate-sensitive processes, such as  pumping water for irrigated agriculture and municipal uses (CENR,
2008).

13(b)  Energy Production

Climate change could affect U.S. energy production and supply (a) if extreme weather events become
more intense, (b) where regions dependent on water supplies for hydropower and/or thermal power plant
cooling face reductions or increases  in water supplies, (c) where changed conditions  affect facility siting
decisions, and (d) where climatic conditions change (positively or negatively) for biomass, wind power,
or solar energy production (Wilbanks et al., 2007; CCSP 2007a).

Significant uncertainty exists about the potential  impacts  of climate change on energy  production and
distribution, in part because the timing and magnitude of climate  impacts are uncertain. Nonetheless,
every existing source of energy in  the U.S. has some vulnerability to climate variability.  Renewable
energy sources tend to be more sensitive to climate variables; but fossil energy production  can also be
adversely effected by air and water temperatures, and the thermoelectric cooling process that is  critical  to
maintaining high electrical generation efficiencies also applies to nuclear energy. In addition, extreme
weather events have adverse effects on energy production, distribution, and fuel transportation (CCSP,
2007a).

Fossil and Nuclear Energy

Climate change impacts on U.S. electricity generation at fossil and nuclear power plants  are  likely to be
similar. The most direct climate impacts  are  related to power plant cooling  and water availability. As
currently  designed, power plants require  significant amounts  of water, and they are vulnerable  to
fluctuations in water supply. Regional scale changes would likely mean that some areas would see
significant increases  in water availability while other regions would see significant decreases. In those
areas seeing a decline, the impact on power plant availability or even siting of new capacity could be
significant. Plant designs are flexible and new technologies for water reuse, heat rejection, and use  of
alternative water sources are being developed; but, at present, some impact—significant on a local level—
can be foreseen (CCSP, 2007a).

Renewable Energy
52 Temperature projections for the State of California are based on IPCC global emission scenarios as discussed in
Section 6(a).
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Because renewable energy depends directly on ambient natural resources such as hydrological resources,
wind patterns and intensity, and solar radiation, it is likely to be more sensitive to climate variability than
fossil or nuclear energy systems that rely on geological stores. Renewable energy systems in the U.S. are
also vulnerable to damage from extreme weather events (CCSP, 2007a).

Hydropower generation  is sensitive to the amount, timing, and geographical pattern of precipitation as
well as temperature (rain or snow, timing of melting).  Reduced stream flows are expected to jeopardize
hydropower production  in  some areas  of the U.S., whereas greater  stream flows, depending on  their
timing, might be  beneficial (Wilbanks  et al., 2007).  In California, where hydropower now comprises
about 15% of in-state energy production,  diminished snow melt flowing through dams will decrease the
potential for hydropower production by up to 30% if temperatures rise to the medium warming range by
the end of the century (5.5-8T (~3.1-4.4°C) increase in California) and precipitation decreases by 10 to
20%.  However, future precipitation projections are quite uncertain so it is possible that precipitation may
increase and expand hydropower generation (California Energy Commission, 2006).

North American wind and  solar resources are about as likely as not  to increase  (medium confidence).
Studies to date project wind resources that are either unchanged by climate change, or reduced by 0-40%.
Future changes in cloudiness could slightly increase the potential for solar energy in North America south
of 60°N, but one study projected that increased cloudiness will likely decrease the output of photovoltaics
by 0-20% (Field et al., 2007).

Bioenergy potential  is  climate-sensitive  through direct impacts on crop growth and availability of
irrigation  water.   Warming  and precipitation increases are expected  to  allow the bioenergy  crop
switchgrass, for instance, to compete effectively with traditional crops in the  central U.S (Field et al.,
2007).  Renewable energy production is  highly susceptible to  localized and  regional  changes in the
resource base. As a  result, the greater uncertainties on regional impacts under current climate change
modeling  pose a significant challenge  in evaluating medium to long-term impacts on renewable energy
production (CCSP, 2007a).

Energy Supply and Transmission

Extreme  weather events can threaten  coastal energy infrastructures and  electricity  transmission  and
distribution infrastructures in  the U.S. and other world regions (Wilbanks et al.,  2007).  Hurricanes in
particular  can have severe impacts on energy infrastructure.  In 2004, hurricane Ivan destroyed seven Gulf
of Mexico oil drilling platforms and damaged 102 pipelines, while hurricanes  Katrina and Rita in 2005
destroyed more than  100 platforms and damaged 558 pipelines (CCSP, 2007a).  Though it is not possible
to attribute the occurrence  of any  singular hurricane to climate change, projections of climate change
suggest that extreme weather  events are very likely to become more intense. If so, then the impacts of
Katrina may be a possible  indicator of the kinds of impacts that could manifest  as a result of climate
change (CCSP, 2007a).

In addition to the direct effects on operating facilities themselves, U.S. networks for transport,  electric
transmission, and delivery would be susceptible to changes due to climate change in stream flow, annual
and seasonal  precipitation patterns, storm severity, and  even  temperature increases  (e.g., pipelines
handling supercritical fluids may be impacted by greater heat loads) (CCSP, 2007a).

U.S. rail transportation lines, which transport approximately 2/3 of the coal to the nation's power plants
(CCSP,  2007a), often closely follow riverbeds. More severe rainstorms can lead to flooding of rivers
which then can wash out or degrade the nearby roadbeds. Flooding  may also disrupt the operation of
inland waterways, the second-most important method of transporting coal. With utilities carrying smaller
stockpiles and projections showing a growing reliance on coal for a majority of the nation's electricity
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production,  any significant  disruption  to the transportation network  has serious implications for the
overall reliability of the grid as a whole. (CCSP, 2007a)

In the  Arctic, soil subsidence caused by the melting of permafrost is a risk to gas and oil pipelines,
electrical transmission towers, and  natural  gas  processing plants  (Wilbanks et al.,  2007).  Along the
Beaufort Sea in Alaska, climate impacts on oil and gas  development in the region are likely to result in
both financial benefits and costs in the  future. For example, offshore oil exploration and production are
likely to benefit from less extensive and thinner sea ice, although equipment will have to be designed to
withstand increased wave forces and ice movement (ACIA, 2004).

13(c)   Infrastructure and Settlements

Climate change vulnerabilities of industry, settlement and society are mainly related to extreme weather
events rather than to gradual climate change. The significance of gradual climate change, e.g., increases
in the  mean temperature, lies mainly  in changes in the  intensity  and frequency of extreme events,
although gradual  changes  can also be associated  with  thresholds  beyond  which impacts  become
significant, such as in the capacities of infrastructures  (Field et al., 2007). Such climate-related thresholds
for human settlements in the U.S. are currently not well understood (Wilbanks et al., 2008).

Extreme weather events could threaten U.S.  coastal energy infrastructure and electricity transmission and
distribution infrastructures.  Moreover, soil subsidence caused by the melting of permafrost in the Arctic
region is a risk to gas and oil pipelines, and electrical transmission  towers. Vulnerabilities of industry,
infrastructures,  settlements and society to  climate  change are generally greater in certain high-risk
locations, particularly coastal and  riverine  areas, and areas  whose  economies are closely linked with
climate-sensitive resources, such as agricultural and forest product industries, water demands and tourism;
these vulnerabilities tend to be localized but are often large and growing (high confidence) (Wilbanks et
al., 2007).  Additionally, infrastructures are often connected, meaning that an impact on one can also
affect others.  For example, an interruption in energy  supply  can  increase heat stress for vulnerable
populations (Wilbanks et al., 2008).

A few studies have projected increasing vulnerability of U.S. infrastructure to extreme weather related to
climate warming unless  adaptation is  effective  (high confidence).  Examples include the  New York
Metropolitan Region, the mid-Atlantic Region, and the urban transportation network  of the Boston
metropolitan area (Wilbanks et al., 2007). In Alaska, examples where infrastructure is projected to be at
"moderate  to high hazard"  in the  mid-21st century include Shishmaref, Nome, Barrow,  the Dalton
Highway, and the Alaska Railroad  (Field et al., 2007). Where extreme weather events become more
intense  and/or more  frequent with climate  change, the  economic and  social costs of those  events will
increase (high confidence) (Wilbanks et al., 2007).

Buildings and Construction

In some Arctic  areas, interactions between climate  warming and inadequate  engineering are causing
problems. The weight of buildings on permafrost is an  important factor; while  many heavy, multi-story
buildings  of northern Russia have  suffered structural  failures, the lighter-weight buildings of  North
America have had fewer such problems  as permafrost has warmed.  Continuous repair and maintenance is
also required for building on permafrost, a lesson learned because many of the buildings that failed were
not properly maintained.  The problems now being  experienced in Russia may be expected to  occur
elsewhere in the Arctic if buildings are not designed and  maintained  to  accommodate  future warming
(ACIA, 2004).
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The cost of rehabilitating community infrastructure damaged by thawing permafrost could be significant.
Even buildings designed specifically for permafrost environments  may be subject to severe damage if
design criteria are  exceeded.   The impervious  nature of ice-rich permafrost has been relied on  for
contaminant  holding facilities, and  thawing such  areas could  result in  severe contamination of
hydrological resources and large cleanup costs, even for relatively small spills (Anisimov et al., 2007).

The construction season in the northern U.S. likely will lengthen with warming.  In permafrost areas in
Alaska, increasing depth of the "active layer" or loss of permafrost can lead to substantial decreases in
soil  strength.   Construction  methods  are  likely to  require  changes in  areas currently underlain by
permafrost, potentially increasing  construction and maintenance cost (high  confidence) (Field et  al.,
2007).

Transportation

In a 2008 report entitled, "Potential Impacts  of Climate Change on U.S. Transportation," the National
Research Council (NRC) issued the following finding:

    Climate change will affect transportation primarily through increases in several types of weather and
    climate extremes, such as very hot days; intense precipitation events; intense hurricanes; drought; and
    rising sea levels, coupled with  storm surges and land subsidence. The impacts will vary by mode of
    transportation and region of the country, but they will be  widespread  and costly in  both human and
    economic terms and will require significant changes in the planning, design, construction, operation,
    and maintenance of transportation systems (NRC, 2008).

NRC states that transportation infrastructure was  designed for typical weather patterns, reflecting local
climate and incorporating assumptions about a reasonable range of temperatures and precipitation levels
(NRC, 2008).  An increase in the  frequency, intensity, or duration of heat spells in the U.S. and other
world regions could cause railroad tracks to buckle, and affect roads through softening and traffic-related
rutting. Warmer or less snowy winters will likely reduce delays, improve ground and air transportation
reliability,  and decrease the  need for winter road maintenance.   More intense winter storms could,
however,  increase risk for traveler safety  and require increased snow removal.  Continuation of the
declining fog trend in at least some  parts of North America should benefit transport (Field et al., 2007).

Warming will likely affect infrastructure for surface transport at high northern latitudes, such as  Alaska.
Permafrost degradation reduces surface  bearing capacity and  potentially triggers landslides.  While  the
season for transport by barge is likely to be extended, the season for ice roads will likely be compressed.
Other types of roads are likely to incur costly improvements in design  and  construction (Field et  al.,
2007).

Similarly, NRC found the following:

    Potentially, the greatest impact of climate  change for North America's transportation systems will be
    flooding of coastal roads, railways, transit systems, and runways because of global rising sea levels,
    coupled with storm surges and exacerbated in some locations by land subsidence (NRC, 2008).

Because of warming, the number of days per year in which travel on the tundra is allowed under Alaska
Department of Natural Resources standards has dropped from over 200 to  about 100 in the past 30 years,
resulting in a 50% reduction in days that oil and gas exploration and extraction can  occur (ACIA, 2004).
Forestry is another industry that requires frozen ground and rivers. Higher temperatures mean thinner ice
on rivers and a longer period during which the ground is thawed.  This leads to a shortened period during
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which timber can  be moved  from  forests to sawmills, and  increasing  problems associated with
transporting wood (ACIA, 2004).

Lakes and river ice  have historically provided major, winter transportation routes and  connections to
smaller settlements in the Arctic.  Reductions in ice thickness will reduce the load-bearing capacity, and
shortening of the ice-season will shorten period of access.  Where  an open-water network is viable, it will
be sensible to increase reliance  on water transport.  In land locked locations, construction of all-weather
roads may be the only viable option, with implications for significantly  increased costs.  Similar issues
will impact the use of sea ice roads primarily used to access offshore facilities (Anisimov et al., 2007).
Loss of summer  sea ice will bring an increasingly navigable Northwest Passage.  Increased marine
navigation and longer summers will improve conditions for tourism and travel associated with research
(Anisimov et al.,  2007).  Along with rising water temperatures,  however, increased  shipping will  also
multiply the risk of marine pests and pollution (Anisimov et al., 2007).

Negative impacts on transportation very likely will include coastal and riverine flooding  and landslides.
Although offset to some degree  by fewer ice threats to navigation,  reduced water depth in the Great Lakes
would lead to "light loading" and adverse economic impacts (Field et al., 2007).

Of all the possible impacts on transportation, the greatest in terms  of cost is that of flooding.  The costs of
delays and lost trips  would be relatively small compared with damage to the infrastructure and to other
property (Wilbanks et al., 2007).

The central Gulf Coast  is particularly vulnerable to climate variability and change because of the
frequency with which hurricanes strike, because much of its land is sinking relative to mean sea level, and
because much of its natural  protection—in the form of barrier islands and wetlands—has been  lost.
While difficult to quantify, the  loss of natural storm buffers will  likely intensify many climate impacts,
particularly in relation to  storm damage (CCSP, 2008f).

Since much of the land in the Gulf Coast is sinking, this area is facing much higher increases in relative
sea level rise (the combination of local land  surface movement and change in mean sea level) than most
other parts of the  U.S. coast.  The CCSP report found that relative sea level rise in the study area is very
likely to increase by at least 0.3  m (1 ft) across the region and possibly as  much as 2 m (6 to  7 ft) in some
parts of the study  area over the next 50 to 100 years. The analysis of even a middle range of potential sea
level rise of 0.3 to 0.9 m (2 to 4 ft) indicates that a vast portion of the Gulf Coast from Houston to Mobile
may be inundated in  the future.  The projected rate of relative sea  level rise for the region during the next
50  to 100 years  is  consistent  with historical trends, region-specific analyses, and  the IPCC Fourth
Assessment  Report  (2007) findings, which  assume no major changes  in ice-sheet  dynamics (CCSP,
2008f).

Twenty-seven percent of the major roads, 9 percent of the rail lines, and 72 percent of the ports in the
region are at or below 122 cm (4 ft) in elevation, although portions of the infrastructure are guarded by
protective structures  such as levees and dikes.  These protective structures could mitigate some impacts,
but considerable land area is still at risk to permanent flooding from rising tides, sinking land, and erosion
during storms. Furthermore, the crucial connectivity of the intermodal system in the area means that the
services of the network can be threatened even if small segments are inundated (CCSP, 2008f).

A great deal of the Gulf Coast study area's infrastructure is subject to temporary flooding associated with
storm surge.  More  than half  (64 percent of interstates;  57 percent of arterials) of the area's major
highways, almost half of the rail miles, 29 airports, and virtually all of the ports are subject to flooding
based on the study of a 5.5- and 7.0-m (18- and 23-ft) storm surge  (CCSP, 2008f).
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Aviation may also be affected.  Increases in precipitation and the frequency of severe weather events
could negatively affect  aviation.  Higher temperatures affect  aircraft performance and  increase the
necessary runway lengths. Some of these risks are expected to be offset by improvements in technology
and information systems (CENR, 2008).

Settlements

According to  IPCC (2007b), "The most vulnerable  industries, settlements and societies are generally
those in coastal and river flood plains, those whose economies are  closely linked with climate-sensitive
resources, and those in areas prone to extreme weather events,  especially where rapid urbanization is
occurring (high  confidence).   Poor communities can be  especially  vulnerable,  in particular those
concentrated in high-risk areas.  They  tend to  have more  limited adaptive capacities, and are more
dependent on climate-sensitive resources such as local water and food supplies (high confidence)".

Effects of climate change on human settlements in the U.S. are very  likely to vary considerably according
to location-specific vulnerabilities, with the  most vulnerable areas  likely to include: Alaska, flood-risk
coastal zones and river basins,  arid areas with associated water scarcity and areas where the economic
base is climate sensitive (CCSP, 2007a).

In Alaska and elsewhere in the Arctic, indigenous communities are facing major economic and cultural
impacts.  Many indigenous peoples depend on hunting polar bear, walrus, seals, and caribou, and herding
reindeer, fishing  and gathering, not only for food and to support the local economy, but also as the basis
for cultural  and social  identity.  Changes in species' ranges and availability,  access to these species, a
perceived reduction in  weather predictability, and travel safety in changing ice and weather conditions
present serious challenges to human health  and  food security, and possibly  even the survival of some
cultures (ACIA, 2004).

Communities in  risk-prone U.S. regions have reason to be  particularly concerned about any potential
increase in severe weather events. The combined effects of severe storms and sea-level rise in coastal
areas or increased risks of fire in drier arid areas are  examples of how climate change may increase the
magnitude of challenges  already facing risk-prone communities. Vulnerabilities may be especially great
for rapidly-growing and/or larger metropolitan areas, where the potential magnitude of both impacts and
coping requirements are likely to be very large. On the other hand, such regions have greater opportunity
to put more adaptable infrastructure in place and make decisions that limit vulnerability (CCSP, 2007a).

Climate  change  has the potential not only to  affect U.S.  communities  directly but also through
undermining their economic bases. In particular, some regional economies  are  dependent  on  sectors
highly sensitive to changes in climate: agriculture, forestry, water resources, or tourism. Climate change
can add to stress  on social and political structures by increasing management and budget requirements for
public services such as public health  care, disaster risk reduction, and even public safety. As sources of
stress grow and combine, the resilience of social and political structures are expected to suffer, especially
in locales with relatively limited social and political  capital (CCSP, 2007a). Additionally, as noted in
Wilbanks et al. (2008), "Human settlements are  the foci for many economic, social, and governmental
processes, and historical experience has shown that catastrophes in  cities can have significant economic,
financial, and political effects much more broadly."

Within settlements experiencing climate  change,  certain parts  of the  population  may  be  especially
vulnerable.  These include the poor, the elderly,  those already in poor health, the disabled, those living
alone, those with limited  rights and power (such as recent immigrants with limited English skills), and/or
indigenous populations dependent  on one or a few resources.  Environmental justice issues  are clearly
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raised through examples  such as warmer temperatures in urban areas having a more direct impact on
those without air-conditioning (Wilbanks et al., 2008).

Finally, growth and development is generally moving toward areas more likely to be vulnerable to the
effects of climate change. For example,  approximately half of the U.S. population, 160 million people,
will live in one of 673 coastal counties by 2008. Coastal residents - particularly those on gently-sloping
coasts - should be concerned about  sea level rise in the longer term, especially if these areas are subject to
severe  storms and storm  surges and/or if their regions are showing gradual land subsidence. Areas that
have been classified as highly vulnerable to climate change (based on measures of physical vulnerability
and adaptive capacity) include  counties  lying along the  east and  west coasts and  Great Lakes, with
medium vulnerability counties mostly inland in the southeast, southwest, and northeast  (CCSP, 2007a).
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Section 14

Ecosystems and Wildlife

This section of the document covers: 1) ecosystem and species-level impacts due to climate change and
elevated CO2 levels, 2) implications for ecosystem services, 3) how climate change effects on extreme
event frequency and intensity may impact ecosystems, and 4) impacts to tourism and recreation.

For North America, the IPCC (Field et al., 2007; Fischlin et al., 200753) concluded:

•   Disturbances  such as wildfire and  insect outbreaks are increasing and are likely to intensify in a
    warmer future with drier soils and longer growing seasons (very high confidence).54  Although recent
    climate trends have increased vegetation growth, continuing increases in disturbances are likely to
    limit carbon  storage, facilitate  invasive species,  and disrupt ecosystem services.   Over the 21st
    century, changes in climate  will  cause  species to  shift north and  to higher  elevations and
    fundamentally rearrange North  American ecosystems.  Differential capacities for range  shifts and
    constraints  from  development, habitat fragmentation, invasive  species,  and broken  ecological
    connections will alter ecosystem structure, function, and services.

14(a)  Ecosystems and Species

Ecosystems, plants, and animals are sensitive to climate variability and always have been. Three clearly
observable connections between climate and terrestrial ecosystems are the seasonal timing of life-cycle
events (referred to as phenology), responses of plant growth or primary production, and the biogeographic
distribution of species (see Figure 14.1).

IPCC reviewed a number of studies describing observations of climate change effects on plant species:
(Field, et al., 2007 and references therein):

•   Between 1981 and 2000, global  daily satellite data indicate earlier onset of spring "greenness" by 10-
    14 days, particularly across temperate latitudes of the Northern Hemisphere.  Field studies conducted
    in the same areas confirm these satellite observations.
    o  Leaves are expanding earlier  (e.g., apple  and grape  plants~2 days/decade  at 72 sites in
       Northeastern U.S.).
    o  Flowering plants are blooming earlier (e.g., lilac - 1.8 days/decade earlier from 1959-1993, at 800
       sites across North America, honeysuckle ~ 3.8 days/decade earlier in the western U.S.).
•   The timing  of autumn leaf senescence55  across  the  continental US,  which  is controlled  by a
    combination of temperature, photoperiod and water deficits, shows weaker trends.

IPCC also discussed several studies showing how North American animals are responding to climate
change,  with effects on phenology,  migration, reproduction, dormancy, and geographic range (Field, et
al., 2007 and references therein):
53 Fischlin et al., 2007 citation refers to Chapter 4, "Ecosystems, Their Properties, Goods, and Services" in IPCC's
2007 Fourth Assessment Report, Working Group II.
54 According to IPCC terminology, "very high confidence" conveys a 9 out of 10 chance of being correct. See Box
1.3 on page 5 for a full description of IPCC's uncertainty terms.
55 The term 'senescence' is defined as the last stage of leaf development that includes changes in pigment
expression, cell death, and eventual leaf drop.
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•   Warmer springs have led to earlier nesting for 28 migrating bird species on the East coast of the U.S.
    and to earlier egg laying for Mexican jays and tree swallows.
•   Several frog species now initiate breeding calls 10-13 days earlier than a century ago in the Upstate
    New York region.
•   In lowland California, 16 of 23 butterfly species advanced the date of first spring flights an average
    24 days over 31 years.
•   Reduced water depth, related to recent warming, in Oregon lakes has increased exposure of toad eggs
    to UV-B, leading to increased mortality from a fungal parasite.
•   The Edith's checkerspot butterfly has become locally extinct in the southern, low elevation portion of
    its western North American range, but  has extended its range 90 km north and  120 m higher in
    elevation.

Changes in phenology vary between species, and the life-cycles of plants, prey animals,  and predators
may shift out of sync, causing species to become  decoupled  from their  resource requirements.   For
example, the decline of long-distance migratory birds in the United States may originate in mistiming of
breeding and food abundance due to differences in phenological shifts in response to climate change
(Scott et al., 2008).

Many North American species, like the Edith's checkerspot butterfly, have shifted their ranges, typically
to the north or to higher elevations (Field, et al., 2007). Migrating to higher elevations with more suitable
temperatures can be  an effective strategy for species if habitat connectivity56 exists and other biotic and
abiotic conditions are appropriate. However, many organisms cannot shift their ranges fast enough to
keep up with the current pace  of climate change (Fischlin et al., 2007).  In addition, species that require
higher-elevation habitat (e.g.,  alpine pikas),  or assemblages for which no substrate  may exist at higher
latitudes (e.g., coral  reefs), often have nowhere to migrate (Fischlin et al., 2007). Cold- and cool-water
fisheries, especially salmonids, have been declining as warmer/drier conditions reduce their habitat (Field
et al., 2007).

The direct effects of elevated CO2 concentrations and climate change to marine ecosystems  include ocean
warming, increased thermal stratification, reduced upwelling, sea level rise, increased  wave height and
frequency, loss of sea ice, and decreases in the pH and carbonate ion concentration of the surface oceans
(see Box 14.1). With lower pH, aragonite (calcium carbonate) that is used  by  many organisms to make
their shells or skeletons will decline or become under-saturated, affecting coral reefs and other marine
calcifiers  (e.g., pteropods-marine  snails). Additional compounding effects, such  as  higher seawater
temperatures  leading to  bleaching events,  or higher seawater temperatures  and nutrients leading to
increased risk of diseases in marine biota will make these ecosystems even more vulnerable to changes in
ocean chemistry along the U.S. and other world regions  (Fischlin, et al.,  2007).  Subtropical and tropical
coral  reefs in  shallow waters  have already  suffered major bleaching events that are clearly driven by
increases  in sea surface temperatures (Janetos et  al.,  2008).  The effects of various other  stressors,
particularly human impacts such as overfishing, pollution, and the introduction of invasive species, appear
to be exacerbating the thermal  stresses on  reef systems and, at least on a local scale, exceeding the
thresholds beyond which coral is replaced by other organisms (Nicholls, et al., 2007).

In the Bering Sea along the Alaskan coast, rising air and sea water temperatures have caused reductions in
sea-ice cover and primary productivity in benthic ecosystems57 (Anisimov et al., 2007). A change  from
Arctic to sub-Arctic conditions is happening with a northward  movement of the pelagic-dominated
56 Connectivity is defined as the degree to which a habitat is physically linked with other suitable areas for a
particular species.
57 Benthic is defined as the deepest environment of a water body which usually includes the seabed or lake floor.
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marine ecosystem that was previously confined to the Southeastern Bering Sea (Anisimov, et al., 2007).
Climate-related impacts observed in the Bering Sea include significant reductions in seabird and marine
mammal populations, increases in pelagic fish, occurrences of previously rare algal blooms, abnormally
high water temperatures, and smaller  salmon runs in coastal rivers (ACIA, 2004). Plants and animals in
polar regions are also vulnerable to attacks from pests and parasites that develop  faster and are more
prolific in warmer and moister conditions (Anisimov, et al., 2007).  See Box 14.1 for more information on
potential climate change impacts to polar bears.

Ecosystem Level Projections

For terrestrial ecosystems across  all world regions,  the  IPCC concluded that substantial changes in
structure and functioning of terrestrial ecosystems are very likely to occur with a global warming greater
than 2 to 3°C above pre-industrial levels  (high confidence) (Fischlin, et al., 2007).  In North America,
disturbances like wildfire and insect outbreaks are increasing and are likely to intensify in a warmer future
with drier soils and longer growing  seasons (very  high confidence) (Field,  et al.,  2007).  Figure 14.1
shows the observed NPP trend in North America between 1981 and 1988.
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Figure 14.1: North American Observations (Field et al., 2007)
                            (c) Forest area burned: Canada
                                                          (d) Relative sea level:
                                                          North American coasts
     (b) Spring bud-burst dates
     Aspen in Edmonton
                           Change in annual mean temperature (°C): 1955 to 2005
Observed trends in some biophysical and socio-economic indicators. Background: change in annual mean
temperature from 1955 to 2005. Insets: (a) trend in April 1 SWE across western North America from 1925-
2002, with a linear fit from 1950-2002, (b) Spring bud-burst dates for trembling aspen in Edmonton since
1900, (c) anomaly in 5-year mean area burned annually in wildfires in Canada since 1930, plus observed
mean summer air temperature anomaly, weighted for fire areas,  relative to 1920-1999, (d) relative sea level
rise from 1850-2000 for Churchill, MB, Pointe-au-Pere, QB,  New York, NY, and Galveston, TX, (e) hurricane
energy (PDI), economic damages, and deaths from Atlantic hurricanes since 1900, and, (f) trend North
American NPP (Net Primary Productivity) from 1981 to 1998. The ten studies upon which the data of this
figure is based are summarized and referenced in Field et al. (2007).
At high latitudes, several models project longer growing seasons and increased net primary productivity
(NPP) as a result of forest expansion into tundra ecosystems. In the mid latitudes,  simulated changes in
NPP  are variable,  depending on whether there is sufficient enhancement  of precipitation  to  offset
increased evapotranspiration in a warmer climate.  By the  end of the 21st century, ecosystems  in the
northeast and southeast U.S. are projected to become carbon sources,  while the western U.S. remains a
carbon sink (Field, et al., 2007).

The  areal extent of drought-limited ecosystems is projected to increase  11%  per °C warming  in the
continental U.S.  Climate change and direct human land-use pressures are both likely to have adverse
impacts on desert ecosystems and species.  Increases in plant productivity resulting from the direct effects
of rising atmospheric CO2 concentrations may partially offset these adverse  effects.   In California,
temperature increases greater than 2°C may lead to the conversion of shrubland into desert and grassland
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ecosystems and evergreen conifer forests into mixed deciduous forests (Fischlin, et al, 2007).  Climate
models suggest a warmer, drier future  climate for the Prairie Pothole Region, which would result in a
reduction in, or elimination of,  wetlands that provide waterfowl breeding habitat (CCSP, 2009d). These
types of regional impacts are indicative of the kinds of changes that can be expected across large parts of
the country.

The  sea-ice biome accounts for a large proportion of primary production in polar waters and supports a
substantial food web. In the Northern  Hemisphere, projections of ocean biological response to climate
warming by 2050 show contraction of the highly productive marginal sea ice biome by 42% (Fischlin, et
al., 2007).  In the Bering Sea, primary productivity in surface waters is projected to increase, the ranges of
some cold-water species will shift north, and ice-dwelling species will  experience habitat loss (ACIA,
2004).

Species Level Projections

After reviewing studies on the projected impacts of climate change on species, IPCC concluded that on a
global scale (Fischlin et al., 2007 and references therein):

•   Projected  impacts  on biodiversity are  significant and  of key  relevance, since  global losses in
    biodiversity are irreversible  (very high confidence).
•   Endemic  species58 richness is  highest where regional  palaeoclimatic changes have  been subtle,
    providing  circumstantial  evidence of their vulnerability to  projected climate change (medium
    confidence).   With  global  average temperature changes of 2°C above pre-industrial levels many
    terrestrial, freshwater, and marine species (particularly endemics across the globe) are at a far greater
    risk of extinction than in the geological past (medium confidence).
•   Approximately 20% to 30% of species (global uncertainty  range from 10% to 40%, but varying
    among regional biota from as  low as 1% to  as high as 80%) will  be at increasingly high risk of
    extinction by 2100.

In North  America, climate change impacts on inland aquatic ecosystems will range from the direct effects
of increased  temperature and  CO2 concentration to indirect  effects  associated with  alterations in
hydrological systems resulting from changes to precipitation regimes and melting glaciers and snow pack
(Fischlin et al., 2007).  For many freshwater animals, such as amphibians, migration to breeding ponds
and the production of eggs is  intimately tied to temperature and moisture availability.  Asynchronous
timing of breeding cycles and pond drying due to the lack of precipitation can lead to reproductive failure.
Differential responses among species  in  arrival or persistence in ponds will likely lead to changes in
community composition and nutrient flow in ponds (Fischlin et al., 2007). Many warm-water and cool-
water (freshwater) fish species will  shift their ranges northward and to higher altitudes. In the continental
U.S., cold-water species will likely disappear from all but the  deeper lakes, cool-water species will be lost
mainly from  shallow  lakes, and  warm  water  species  will  thrive except  in  the  far south,  where
temperatures in shallow lakes will exceed survival thresholds (Field et al., 2007).  See also section 9(f) for
a discussion of climate change impacts to freshwater and marine fish populations.

Bioclimate modeling based on output from five general circulation models (GCMs) suggests that  on the
long (millennial) timescale there may be decreases of bird and mammal species richness in warmer, low
elevation areas, but increases in cold high elevation zones, and increases  of reptile species richness in all
areas.  Over the next century, however, even positive long-term species richness  may lead to short term
decreases because species that are  intolerant of local conditions may disappear relatively quickly while
 ! Endemic species are unique to their location or region and are not found anywhere else on Earth.
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migration of new species into the area may be quite slow (Field et al., 2007; Currie, 2001). Changes in
plant species composition in response to  climate change can increase  ecosystem vulnerability to other
disturbances, including fire and biological  invasion. There are other possible, and even probable, impacts
and changes in biodiversity-related relationships (e.g., disruption of the interactions between pollinators,
such as bees, and flowering plants), for which we  do not yet have a substantial observational database
(Janetos et al., 2008).

On small oceanic islands with  cloud forests or high elevation ecosystems, such as the Hawaiian Islands,
extreme elevation  gradients exist, ranging  from  nearly  tropical to  alpine  environments.   In these
ecosystems,  anthropogenic  climate change,  land-use changes,  and  biological invasions  will work
synergistically to drive several  species (e.g., endemic birds) to extinction (Mimura et al., 2007).

According to IPCC, climate  change (very high confidence) and ocean acidification (see Box 14.1) due to
the direct  effects  of elevated  CO2 concentrations  (medium confidence) will  impair  a wide  range of
planktonic and other marine  organisms that use aragonite to make their shells or skeletons (Fischlin et al.,
2007).  Average pH for the ocean surface is projected to decrease by up to 0.3-0.4 units by 2100 (Fischlin
et al., 2007).   These  impacts could result  in  potentially  severe ecological  changes to tropical  and
coldwater marine ecosystems where carbonate-based phytoplankton and corals are the foundation for the
trophic system (Schneider et al., 2007).  The IPCC concluded that it is very likely that a projected future
sea surface temperature increase of 1 to 3°C will result in more frequent bleaching events and widespread
mortality,  if there  is  not thermal adaptation or acclimatization by corals and their algal symbionts
(Nicholls et al.,  2007). The ability of coral reef ecosystems to withstand the impacts of climate change
will depend to a large degree on the extent of degradation from other anthropogenic pressures (Nicholls et
al., 2007).
  Box 14.1: Ocean Acidification Effects on Marine Calcifiers

  Elevated atmospheric concentrations of greenhouse gases impact the health of marine calcifiers by changing the
  physical and chemical properties of the oceans. Calcifiers play important roles in marine ecosystems by serving as
  the base of food chains, providing substrate, and helping to regulate biogeochemical cycles (Fischlin et al., 2007).

  Ocean acidification lowers the saturation of calcium carbonate (CaCO3) in sea water, making it more difficult for
  marine calcifiers to build shells and skeletons (Fischlin et al., 2007). The IPCC (Denman et al., 2007) made the
  following statements regarding ocean acidification:
      •   The biological production of corals, as well as calcifying photoplankton and zooplankton within the water
         column, may be inhibited or slowed down as a result of ocean acidification;
      •   Cold-water corals are likely to show large reductions in geographic range this century.
      •   The dissolution of CaCO3 at the ocean floor will be enhanced, making it difficult for benthic calcifiers to
         develop protective structures;
      •   Acidification can influence the marine food web at higher trophic levels.

  The impacts of elevated CO2 concentrations on oceanic chemistry will likely be greater at higher latitudes (Fischlin
  et al., 2007). Polar and sub-polar surface waters and the Southern Ocean are projected to be aragonite (a form of
  CaCO3) under-saturated by 2100, and Arctic waters will be similarly threatened (Denman et al., 2007).  These
  impacts will likely threaten ecosystem dynamics in these areas where marine calcifiers play dominant roles in the
  food web and in carbon cycling (Fischlin et al., 2007).

  The overall reaction of marine biological carbon cycling and ecosystems to a warm and high-CO2 world is not yet
  well understood. In addition, the response of marine biota to  ocean acidification is not yet  clear, both for the
  physiology of individual organisms and for ecosystem functioning as a whole (Denman et al., 2007).
For the Arctic, IPCC (Anisimov et al., 2007 and references therein) concluded that:
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    Decreases in the abundance of keystone species59 are  expected to be the primary factor in causing
    ecological cascades60 and other changes to ecological dynamics.
    Arctic animals are likely to be most vulnerable to warming-induced drying of small water bodies;
    changes in snow cover and freeze-thaw cycles that affect access to food (e.g., polar bear dependence
    on  sea ice for seal hunting  -  see Box  14.2) and protection from predators  (e.g., snow  rabbit
    camouflage in snow); changes that affect the timing of behavior (e.g., migration  and reproduction);
    and influx of new competitors, predators, parasites, and diseases.
    In the past, sub-arctic species have been unable to live at higher latitudes because of harsh conditions.
    Climate change  induced warming will increase the rate  at  which  sub-arctic species are able to
    establish.  Some non-native species, such as the North American mink, will become invasive, while
    other species that have already colonized some Arctic  areas are likely to expand  into other regions.
    The spread of non-native, invasive plants  will likely have adverse impacts on native plant species.
    For example,  experimental warming and nutrient addition has shown that native mosses  and lichens
    become less abundant when non-native plant biomass increases.
    Bird migration routes and  timing are  likely to change as the availability of suitable habitat  in the
    Arctic decreases.
    Loss of sea ice will impact species, such as harp seals, which are dependent on it for survival.
    Climate warming is likely to increase the incidence of pests, parasites, and diseases such  as musk ox
    lung worm and abomasal nematodes of reindeer.
  Box 14.2: Polar bears (adapted from Box 4.3 in Fischlin, et al., 2007)
  There are an estimated 20,000 to 25,000 polar bears (Ursus maritimus) worldwide, mostly inhabiting the annual sea ice
  over  the continental shelves  and inter-island archipelagos of the circumpolar Arctic.  Polar bears  are specialized
  predators that hunt ice-breeding seals and are therefore dependent on  sea ice for survival.  After emerging in spring
  from a 5 to 7 month fast in nursing dens, females require immediate nourishment and thus depend on close proximity
  between land and sea ice before the sea ice breaks up.  Continuous access to sea ice allows bears to hunt throughout the
  year, but in areas where the sea ice  melts completely each summer, they are forced to spend several months in tundra
  fasting on stored fat reserves until freeze-up (Fischlin, et al., 2007).

  The two Alaskan populations (Chukchi Sea- -2,000 individuals in 1993, Southern Beaufort Seas- -1,500 individuals in
  2006) are vulnerable to  large-scale dramatic seasonal fluctuations  in ice movements  because of the  associated
  decreases in abundance and access  to prey and increases in the energetic costs of hunting (FWS, 2007).  The IPCC
  projects that with a warming of 2.8°C above pre-industrial temperatures and associated declines in sea ice, polar bears
  will face a high risk of extinction. Other ice-dependent species (e.g., walruses - for rest; small whales - for protection
  from predators) face similar consequences, not only in the Arctic but also in the Antarctic (Fischlin, et al., 2007).

  In 2005, the World Conservation Union's (IUCN) Polar Bear Specialist Group concluded that the IUCN Red  List
  classification for polar bears  should be upgraded from Least  Concern to  Vulnerable based on the likelihood of an
  overall decline in the size of  the total  population of more than 30% within the next 35 to 50 years (Fischlin, et al.,
  2007).  In May 2008, the U.S. Fish and Wildlife Service  listed the polar bear as a threatened species under the
  Endangered Species Act.  This decision was based on scientific evidence showing that sea ice loss threatens, and  will
  likely continue to threaten, polar bear habitat (FWS, 2008).
59 Keystone species is defined as a species that has a disproportionate effect on its environment relative to its
abundance or total biomass. Typically, ecosystems experience dramatic changes with the removal of such a species.
60 Ecological cascades are defined as sequential chains of ecological effects, including starvation and death,
beginning at the bottom levels of the food chain and ascending to higher levels, including apex predators.
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14(b)  Ecosystem Services

Ecosystems provide many goods and services that are of vital importance for biosphere function and
provide the basis for the delivery of tangible benefits to humans. These services include: maintenance of
biodiversity, nutrient regulation, shoreline protection, food and habitat provisioning, sediment control,
carbon sequestration, regulation of the water cycle and water quality, protection of human health, and the
production of raw materials (Fischlin et al., 2007).  Climate change is projected to have an increasing
effect on the provisioning of ecosystem  services  in the U.S.  Increasing temperatures  and shifting
precipitation patterns, along with the direct effects of elevated CO2 concentrations, sea level rise, and
changes in climatic variability, will affect the quantity and quality of these  services.  By the end of the
21st century, climate change and its impacts may be the dominant driver of biodiversity loss and changes
in ecosystem services globally (Millennium Ecosystem Assessment-Synthesis, 2005).

Many U.S. ecosystems and the services they provide are already threatened by natural and anthropogenic
non-climate stressors.  Climate-related  effects on ecosystems services will  amplify the effects of non-
climate stressors.  Multiple U.S. industries,  such as timber, fisheries, travel, tourism,  and agriculture that
are  already threatened could face substantially greater  impacts with  concurrent  effects  on financial
markets (Ryan et al., 2008; Field et al., 2007).

14(c)  Extreme Events

Many significant impacts of climate change  on U.S. ecosystems  and wildlife may emerge through
changes  in the intensity and the frequency  of  extreme weather  events.    Extreme events,  such as
hurricanes, can  cause mass mortality in wildlife populations and contribute significantly to alterations in
species distribution and abundance following the disturbance.  For example,  the aftermath of a hurricane
can cause coastal forest to die from storm surge-induced salt deposition, or wildlife may find it difficult to
find food, thus  lowering the chance of  survival.  Droughts play an important role in forest dynamics as
well, causing pulses of tree mortality in the North American woodlands. Greater intensity and frequency
of extreme events may alter disturbance  regimes  in North  American  coastal ecosystems leading to
changes  in diversity and ecosystem functioning  (Field  et al., 2007; Fischlin et al., 2007).  Species
inhabiting saltmarshes, mangroves, and  coral reefs are likely to be particularly vulnerable to these effects
(Fischlin et al., 2007).  Higher temperatures, increased drought, and more intense thunderstorms will very
likely increase erosion and promote invasion of exotic grass species in arid lands (Ryan et al.,  2008).

14(d)  Implications for Tribes

North American indigenous  communities  whose health, economic well-being, and cultural traditions
depend upon the natural environment will likely be affected by the degradation of ecosystem goods and
services associated with climate change (Field et al., 2007).  Among the most climate-sensitive North
American communities are those of indigenous populations dependent on one or a few natural resources.
About 1.2 million (60%) of U.S. tribal members live on or near reservations, and many pursue lifestyles
with a mix of traditional subsistence activities and wage labor (Field et al., 2007).

In Alaska and elsewhere in the  Arctic,  indigenous communities are  facing major economic  and cultural
impacts.  Many indigenous peoples depend on hunting polar bear, walrus, seals, and caribou, and herding
reindeer, fishing and gathering, not only for food and to support the local economy,  but also as the basis
for cultural and social identity. These livelihoods are already being threatened by multiple climate-related
factors,  including reduced or displaced populations of marine  mammals, caribou,  seabirds, and other
wildlife,  losses  of forest resources due to  insect damage, and reduced/thinner sea ice, making hunting
more difficult and dangerous (ACIA, 2004).
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14(e)  Implications for Tourism

The  U.S. ranks among the top ten nations for international tourism receipts (US $112 billion), having
domestic tourism and outdoor recreation markets that are several times larger than most other countries.
Nature-based tourism is a major market segment in North America, with over 900 million visitor-days in
national/provincial/state parks  in  2001.   Climate variability affects many segments of this growing
economic sector. For example, wildfires in Colorado (2002) caused tens of millions of dollars in tourism
losses by reducing visitation and destroying infrastructure. Similar economic losses during that same year
were caused by drought-affected water levels in rivers and reservoirs in the western U.S. and parts of the
Great Lakes.  The ten-day closure  and clean-up following Hurricane Georges (September 1998) resulted
in tourism  revenue losses of  approximately US $32  million in the Florida Keys. While the North
American tourism industry acknowledges  the important influence of climate, its impacts have not been
analyzed comprehensively (Field et al., 2007 and references therein).
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                               PartV

   International Observed and Projected Human Health and Welfare
                    Effects from Climate Change
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Section 15

International  Impacts

The  primary  focus  of this document is on the observed and potential future  impacts  associated with
elevated  GHG concentrations and  associated climate change  within the  U.S.  However, EPA has
considered the global nature of climate change in at least two ways for purposes of this document.

First, GHGs,  once emitted, remain in the atmosphere for decades to centuries, and thus become, for all
practical purposes, uniformly mixed in the atmosphere, meaning that U.S. emissions have climatic effects
not only  in the U.S. but in all parts of the world.  Likewise, GHG emissions from other countries can
influence the  climate of the U.S., and therefore affect human health, society and the natural environment
within the U.S. All  observed and potential future climate change impacts within the U.S. reviewed in this
document consider climate change driven by global anthropogenic GHG emissions.

Second, despite  widely discussed  metrics  such  as  global  average temperature,  climate change  will
manifest itself very differently in different parts of the world, where regional changes in temperatures and
precipitation patterns, for example,  can  deviate significantly from changes in the global average.  This
regional variation in climate change, coupled with the fact that countries are in  very different positions
with respect to their vulnerability and adaptive capacity, means that the  impacts of climate change will be
experienced very differently in different parts of the world.  In general, the  relatively poor nations may
experience the most severe impacts, due to their heavier reliance on  climate-sensitive  sectors such as
agriculture and tourism, and due to their lack of resources for increasing resilience and adaptive capacity
to climate change (see Parry et al., 2007). In addition to the fact that U.S. GHG emissions may contribute
to these impacts (see Section 2 for a comparison of U.S. total and transportation emissions to other
countries' emissions), climate change impacts in certain regions of the world may exacerbate problems
that raise humanitarian and national security issues for the U.S.

15(a)  National Security

A number of analyses and publications, both inside  and outside the government, have focused on the
potential U.S. national security implications of climate change.

A public report prepared for the Department of Defense (Schwartz and Randall, 2003) examined what the
effects on U.S.  national security might be  from an abrupt climate  change scenario.61   The authors
concluded that the  resultant climatic conditions could  lead to resource constraints and potentially de-
stabilize the global geo-political environment, with resultant national security  concerns for the U.S.

The  Arctic Climate Impact Assessment (2004)  raised security issues,  stating that as Arctic sea ice
declines,  historically closed sea passages will open,  thus raising questions  regarding sovereignty over
shipping  routes and ocean resources. In IPCC (Anisimov, 2007), a study shows projections suggesting
that by 2050,  the Northern Sea Route will have  125 days per year with less than 75% sea-ice cover, which
represents  favorable  conditions for navigation  by  ice-strengthened  cargo ships.   This may  have
implications for trade and tourism as well.
61 The abrupt climate change used for the study was the unlikely, but plausible, collapse of the thermohaline
circulation in the Atlantic, modeled after an event that occurred 8,200 years ago.
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The  Center for Naval Analyses (CNA) Corporation, a non-profit national  security analysis institution,
issued a report entitled National Security and the Threat of Climate Change (2007), in which a dozen
retired generals and admirals were briefed by climate change scientists and business leaders over the
course of many months and then tasked with providing their own views and recommendations about the
linkage between  climate change  and national  security over the next 30  to  40 years.   Among their
conclusions was that climate change acts as a "threat multiplier" for instability in some of the most
volatile regions of the world.  "Projected climate change will seriously exacerbate already marginal living
standards  in many Asian, African, and Middle  Eastern nations,  causing widespread political instability
and the likelihood of failed  states," said the authors.  Regarding the potential impact of climate change on
military systems,  infrastructure  and operations, the report stated that climate change will stress the U.S.
military by affecting weapons systems and platforms, bases,  and military operations.  A U.S. Navy (2001)
study was cited which states that an ice-free Arctic will require an increased scope for naval operations.
Given these concerns, one of the recommendations of the CNA (2007) report was for the Department of
Defense to conduct an assessment of the impact on U.S. military installations worldwide of rising  sea
levels, extreme weather events, and other possible climate change  impacts over the next 30 to 40 years.

The U.S. Congress has expressed national security concerns due to climate change by requesting that the
defense and intelligence  communities examine these  linkages.   H.R.  4986, passed in January  2008,
requires the Department of Defense to consider the effect of climate change on its facilities, capabilities
and missions.  Specific directives in the bill include that future national security strategies and national
defense strategies must include guidance for military planners to assess the risks of projected climate
change  on current and future armed forces missions, as well  as  update defense plans based upon these
assessments (H.R. 4986, 2008).

In June 2008 testimony before the House, Dr. Thomas Fingar, Deputy Director of National Intelligence
for Analysis, laid out a national intelligence  statement on the U.S.  national security implications from
climate change projected out to 2030.  Using a broad definition for national security,62 the assessment
found that:

        "[G]lobal climate change will have wide-ranging implications for U.S. national security interests
        over the next 20 years...We judge that the most significant impact for the United States will be
        indirect and result  from climate-driven effects on  many other countries and their potential to
        seriously  affect U.S. national security interests. We assess that climate change alone is unlikely
        to trigger state failure in any state out to 2030, but the impacts will worsen existing problems—
        such  as poverty, social tensions, environmental degradation,  ineffectual leadership,  and  weak
        political institutions. Climate change could threaten domestic stability in some states, potentially
        contributing to intra- or, less likely, interstate conflict, particularly over access to increasingly
        scarce water resources." (Fingar, 2008)

Building on that  work, the National Intelligence Council in November  2008,  in its publication Global
Trends 2025: A Transformed World, discussed climate change impacts prominently. The report posed a
scenario named "October Surprise," which discussed the economic and sociopolitical ramifications of an
extreme flooding event linked to global climate change in New York City in 2020 (NIC, 2008).
62 This definition considered if the effects would directly impact the U.S. homeland, a U.S. economic partner, or a
U.S. ally. Additionally, the potential for humanitarian disaster was focused on as well as if an effect would result in
degrading or enhancing an element of national power. For more information, see Fingar, 2008.
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15(b)   Overview of International Impacts

The IPCC Working Group II volume of the Fourth Assessment Report reviews the potential impacts in
different regions of the world. The IPCC (Parry et al., 2007) identifies as the most vulnerable regions:

    •    The Arctic, because of high rates of projected warming on natural systems;
    •    Africa, especially the sub-Saharan  region, because of current low adaptive capacity as well as
        climate change;
    •    Small islands, due to high exposure of population and infrastructure to risk of sea-level rise and
        increased storm surge;
    •    Asian mega deltas, such as the Ganges-Brahmaputra and the Zhujiang, due to large populations
        and high exposure to sea level rise, storm surge and river flooding.

Table 15.1 summarizes the vulnerabilities and projected impacts for different regions of the world, as
identified  by IPCC (2007b). And  the paragraphs that follow  provide some  additional detail  for key
sectoral impacts that have  received attention by the research community.  There  is currently a lack of
information about how these potential impacts in other regions of the world may influence international
trade and migration patterns, which in turn could raise concerns for the U.S.

On a global basis, according to IPCC, "projected climate change-related exposures are likely to affect the
health status of millions of people, particularly those with low adaptive capacity," through several factors
including "the increased frequency of cardio-respiratory diseases due to higher concentrations of ground
level ozone related to climate change (IPCC, 2007b)." More specifically, "cities that currently experience
heat waves are expected to be further challenged by an increased number, intensity and duration of heat
waves during the course of the century, with potential for adverse health impacts."

Mosquito-borne diseases  which are sensitive to climate change,  such as dengue and malaria are of great
importance  globally.  Studies cited  in Confalonieri et al. (2007)  have reported associations between
spatial,  temporal, or spatiotemporal patterns  dengue  and climate, although these are  not  entirely
consistent.   Similarly, the  spatial distribution, intensity of transmission, and seasonality of malaria is
observed to be influenced by climate in sub-Saharan Africa (Confalonieri et al., 2007). In other world
regions  (e.g., South America, continental regions of the Russian Federation) there is no clear evidence
that malaria has  been affected  by climate change (Confalonieri et  al., 2007).  Changes  in reporting,
surveillance, disease control measures, population changes and other factors such as land use change must
to be taken into  account when attempting to attribute changes in human diseases  to climate change
(Confalonieri et al., 2007).

Food production is expected to be much more vulnerable to climate change in poorer regions of the world
compared to food production in the  U.S. and other high, northern  latitude regions.  The IPCC (2007b)
stated with medium confidence63 that, at lower latitudes, especially seasonally dry and tropical regions,
crop productivity is projected to decrease for even small local temperature increases  (1-2°C; ~2-3.5°F),
which would increase risk of hunger. Furthermore, increases in the  frequency of droughts and floods are
projected to affect local production negatively, especially in subsistence sectors at low latitudes. Drought
conditions, flooding, and pest outbreaks are some of the current stressors  to food security that may be
influenced by future climate change.  Sub-Saharan Africa is currently highly vulnerable to food insecurity
(Easterling et al., 2007).  A study cited by Easterling et al. (2007)  projected increases in carbon storage
on croplands globally under climate change  up to 2100, but found  that ozone damage to crops could
significantly offset these gains.
63 According to IPCC terminology, "medium confidence" conveys a 5 out of 10 chance of being correct. See Box
1.3 on page 5 for a full description of IPCC's uncertainty terms.
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Regarding global forest production, the IPCC (Easterling et al., 2007) concluded that forestry production
is estimated to change modestly with climate change in the short and medium term (medium confidence).
The projected change in global forest products output ranges from a modest increase to a slight decrease,
with significant variations  regionally.  There  is projected to be a production shift from low latitude
regions in the short-term, to high latitude regions in the long-term.  Projected changes in the frequency
and severity of extreme climate events have  significant consequences for forestry production in addition
to impacts of projected mean climate (high confidence)  (Easterling et al., 2007).  Climate variability and
change also modify the risks of fires, and pest and pathogen outbreaks, with negative consequences for
forestry (high confidence) (Easterling et al., 2007).

The  IPCC made the following conclusions when considering how climate change may affect water
resources  across all world regions:

•   The impacts of climate change on freshwater systems and their management are mainly  due to the
    observed and projected increases in temperature, sea level, and precipitation variability (very high
    confidence) (Kundzewicz et al., 2007).
•   All regions show an overall net negative  impact of climate change on water resources and freshwater
    ecosystems (high confidence).  Areas in which runoff is projected to  decline are likely  to face a
    reduction in the value  of the services provided by water resources  (very high  confidence).   The
    beneficial impacts of increased annual runoff in other areas will be tempered by negative effects due
    to increased precipitation variability and seasonal runoff shifts on water supply,  water quality, and
    flood  risk (high confidence) (Kundzewicz et al., 2007).
•   Climate change affects the function and operation  of existing water infrastructure as well as water
    management practices.  Adverse  effects of climate change  on  freshwater systems  aggravate the
    impacts of other stresses, such as population growth, changing economic activity, land use change,
    and urbanization.  Globally,  water demand will grow  in the  coming decades, primarily due to
    population growth and increased affluence; regionally, large changes in irrigation water demand as a
    result of climate changes  are  likely.  Current water  management practices are very likely to be
    inadequate  to reduce negative impacts  of climate  change on  water supply reliability, flood risk,
    health, energy, and aquatic ecosystems (very high confidence)  (Kundzewicz et al., 2007).
•   In  polar  regions, components of the terrestrial cryosphere  and hydrology are increasingly being
    affected by climate change.  Changes to cryospheric processes64 are also modifying seasonal runoff
    (very high confidence) (Anisimov et al., 2007).

The  IPCC (Nicholls et al., 2007) identified that coasts are experiencing the adverse consequences of
hazards related to climate and sea level (very high confidence).  They are highly vulnerable to extreme
events, such as storms which impose substantial costs  on coastal societies. Through the 20th century,
global  rise of sea level contributed to increased coastal inundation, erosion, and ecosystem losses, but
with considerable local and regional variation due to other factors (Nicholls et al., 2007).

The IPCC (Fischlin et al., 2007) recently made the following conclusions when considering how climate
change may affect ecosystems across all world regions:

•   During the course of this century the resilience  of many ecosystems is likely to be exceeded by an
    unprecedented combination of changes in climate and in other global change drivers (especially land
    use, pollution, and overexploitation), if greenhouse gas emissions and other changes continue at or
    above current rates (high confidence).  The elevated CO2 levels and associated climatic changes will
64 Cryospheric processes are defined to include the annual freezing and melting of snow cover, ice sheets, lake and
river ice, permafrost, and sea ice.
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    alter  ecosystem structure, reduce  biodiversity,  perturb functioning  of  most  ecosystems,  and
    compromise the services they currently provide (high confidence). Present and future land use change
    and associated landscape fragmentation are very likely to impede species' migrations and geographic
    range shifts in response to changes in climate (very high confidence).
•   Ecosystems and species are very likely to show a wide range of vulnerabilities to climate change,
    depending  on the extent to which climate  change alters  conditions that could  cross critical,
    ecosystem-specific thresholds (very high confidence). The most vulnerable ecosystems include coral
    reefs, the sea  ice biome and other high latitude ecosystems (e.g. boreal forests), mountain ecosystems
    and Mediterranean-climate ecosystems65  (high confidence).   Least vulnerable ecosystems  include
    savannas and  species-poor deserts, but this assessment is especially subject to uncertainty relating to
    the CO2 fertilization effect and disturbance regimes such as fire (low confidence).
       iykJ^                                                              	

Africa    •  New studies confirm that Africa is one  of the most  vulnerable continents to climate
             variability and change because of multiple stresses and  low adaptive capacity. Some
             adaptation to current climate variability is taking place; however, this may be insufficient for
             future changes in climate.
          •  By  2020, between 75 million and  250 million  people  are projected to  be exposed  to
             increased water stress due to climate change. If coupled with  increased demand, this will
             adversely affect livelihoods and exacerbate water-related problems.
          •  Agricultural production, including access to food, in many countries and regions is projected
             to be severely compromised by climate  variability  and change.  The  area suitable for
             agriculture, the length of growing seasons and yield potential, particularly along the margins
             of semi-arid and arid areas,  are expected to decrease. This would further adversely affect
             food security and exacerbate malnutrition  in the  continent. In some countries, yields  from
             rain-fed agriculture could be reduced by up to 50% by 2020.


Asia      •  Glacier  melt in the Himalayas is projected to increase flooding, and rock avalanches  from
             destabilized slopes, and to affect water resources within the next  two to  three decades.
             This will be followed by decreased river flows as the glaciers recede.
          •  Freshwater availability in  Central, South,  East and South-East Asia,  particularly in large
             river basins, is projected to decrease due to climate  change which, along  with population
             growth  and  increasing demand arising from higher  standards of living, could  adversely
             affect more than a  billion people by the 2050s.
          •  Coastal areas, especially heavily-populated mega delta regions in South, East and South-
             East Asia, will be at greatest risk due to increased flooding from the sea and, in some mega
             deltas, flooding from the rivers.
          •  It is projected that  crop yields could  increase up to 20% in East and South-East Asia while
             they could decrease up to  30% in Central and South Asia by the mid-21 st century. The risk
             of hunger is projected to remain very high in several developing countries.
          •  Endemic morbidity and mortality due to diarrhea disease primarily  associated with floods
             and droughts are expected to rise  in  East,  South  and South-East Asia due to projected
             changes in the hydrological  cycle associated with global warming. Increases in coastal
             water temperature would  exacerbate  the  abundance and/or toxicity of cholera  in South
             Asia.
65 Mediterranean climate ecosystems feature subtropical climate with dry summers. Despite the name, these
ecosystems exist in the US along the coasts of central and southern California.
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Latin     •  By  mid-century, increases in temperature  and associated decreases in  soil water are
America     projected to lead to gradual replacement of tropical forest by savanna in eastern Amazonia.
             Semi-arid  vegetation will tend to be replaced by  arid-land vegetation. There is a risk of
             significant  biodiversity  loss through species  extinction  in many  areas  of tropical  Latin
             America.
          •  In  drier areas,  climate change  is expected to lead to salinization and  desertification of
             agricultural land. Productivity  of  some important crops is  projected to  decrease  and
             livestock productivity to decline, with adverse consequences for food security. In temperate
             zones soybean  yields are projected to increase.
          •  Sea-level rise is projected to cause increased  risk  of flooding in low-lying  areas. Increases
             in sea surface temperature due to climate change are projected to have adverse effects on
             Mesoamerican coral reefs, and cause shifts in the location of south-east Pacific fish stocks.
          •  Changes in precipitation  patterns  and the disappearance of glaciers  are  projected to
             significantly affect water availability  for human  consumption,  agriculture  and  energy
             generation.


Polar     •  For human communities  in the Arctic, impacts, particularly those resulting  from changing
Regions     snow and  ice conditions, are projected to be mixed.  Detrimental impacts would  include
             those on infrastructure and traditional indigenous ways of life.
          •  Beneficial  impacts would include reduced heating  costs and more navigable  northern sea
             routes.
Small     •  Small islands, whether located in the tropics or higher latitudes, have characteristics which
Islands      make them especially vulnerable  to the  effects  of climate change,  sea-level rise  and
             extreme events.
          •  Deterioration in  coastal conditions, for  example through erosion of beaches and coral
             bleaching,  is expected to  affect  local resources, e.g., fisheries, and reduce the value of
             these destinations for tourism.
          •  Sea-level rise is expected to exacerbate inundation, storm surge, erosion and other coastal
             hazards,  thus  threatening vital infrastructure,  settlements  and facilities  that support the
             livelihood of island communities.
          •  Climate change  is  projected  by mid-century to reduce water resources in many small
             islands, e.g., in the  Caribbean and Pacific, to the point where they become insufficient to
             meet demand during low-rainfall periods.

* With the exception of some very high confidence statements for small islands, all other IPCC conclusions within the
                                      	
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    G.C. Hegerl, M. Heimann, B. Hewitson, B.J. Hoskins, F. Joos, J. Jouzel, V. Kattsov, U. Lohmann, T. Matsuno,
    M. Molina, N. Nicholls, J. Overpeck, G. Raga, V. Ramaswamy, J. Ren, M. Rusticucci, R. Somerville, T.F.
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Stevenson, D.S.,  et al. (2005) Impacts of climate  change and variability on tropospheric ozone and its precursors.
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USDA (2007) Crop Production Historical Track Records, National Agricultural Statistics Service (NASS):
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U.S. EPA (2008) Inventory of U.S.  Greenhouse Gas Emissions  and Sinks: 1990 - 2006. EPA-430-R-08-005,
    Washington, DC.
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 Appendix A:  Brief Overview of Adaptation

Adaptation to climate change is the adjustment in the behavior or nature of a system to the effects of
climate change.  In the process  of developing information  to support the Administrator's decision
regarding whether elevated combined  greenhouse gas  (GHG)  concentrations endanger public health or
welfare, various questions were raised about the relevance of adaptation. As noted in the Introduction,
this document does not focus on adaptation because it (like GHG mitigation) is essentially a response to
any known  and/or perceived risks  due to climate change.  Although adaptation was  not  considered
explicitly in the document, it does note where the underlying references already take into  account certain
assumptions about adaptation  when projecting future risks and impacts due  to  climate  change. This
appendix provides a brief review of the state of knowledge pertaining to adaptation.

What is Adaptation?

As defined in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (2007),

    Adaptation to climate change takes place through adjustments to reduce vulnerability or enhance
    resilience in response to observed or expected changes in climate and associated extreme weather
    events. Adaptation occurs in physical, ecological and human systems. It involves changes in social
    and environmental processes, perceptions of climate risk, practices and functions to reduce potential
    damages or to realise new opportunities.

Adaptations vary according to the  system in which they occur, who undertakes them, the climatic stimuli
that prompts them, and their timing, functions, forms and effects.  Adaptation can be of two broad types:

    •   Reactive or autonomous adaptation is the process by which species and ecosystems respond to
       changed conditions.   An example  is  the  northward  migration of a species  in response to
       increasing temperature.

    •   Anticipatory adaptation is planned  and implemented before  impacts of climate change are
       observed. An example is  the construction of dikes in  response to (and to prepare for) expected
       sea level rise.

Summary of the Scientific Literature on Adaptation

    1.  There is experience with adapting to weather,  climate variability and the current and projected
       impacts of climate change.

       o  There is a  long  record of practices to  adapt to the impacts of weather as  well as natural
           climate variability. These practices include proactive steps like water storage and crop and
           livelihood diversification,  as  well  as reactive or ex-post  steps like  emergency response,
           disaster recovery and migration.66

       o  The IPCC (2007) states - with very high confidence67 - that "Adaptation to climate change is
           already taking place, but on a limited basis."68
66Adgeretal. (2007), p. 720
  A set of terms to describe uncertainties in current knowledge was used throughout IPCC's Fourth Assessment
Report. On the basis of a comprehensive reading of the literature and their expert judgment, IPCC authors assigned
a confidence level to major statements on the basis of their assessment of current knowledge, as follows:
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        o  A wide array of adaptation options is available, ranging from purely technological (i.e., sea
           walls), through behavioral changes (i.e., altered food and recreational choices), to managerial
           (e.g. altered farm practices), and to policy (e.g. planning regulations).69

        o  Some  programs have  developed  strategic plans for responding to  climate change.   An
           example of such a plan is EPA's National Water Program Strategy: Response to Climate
           Change (EPA, 2008).
    2.  Although  adaptation  options are  known,  available  and  used in some places, there  are
       significant barriers to their adoption.

       o  The IPCC states with very high confidence that "there are substantial limits and barriers to
           adaptation."  These  include  formidable  environmental,  economic, informational,  social,
           attitudinal and behavioral barriers to the implementation of adaptation that  are not fully
           understood.70  The IPCC also states that there are significant knowledge gaps for adaptation
           as well as  impediments to flows  of knowledge and  information  relevant to adaptation
           decisions.71

    3.  Current scientific information does not provide  sufficient information to assess how effective
       current and future adaptation options will be at reducing vulnerability to the impacts of climate
       change. The fact that a country has a high capacity to adapt to climate change does not mean
       that its actions will be effective at reducing vulnerability.

       o  While  many technologies and  adaptation strategies are known and developed  in some
           countries, the available scientific literature does not indicate how effective various options are
           at fully reducing risks, particularly at higher levels of warming  and  related impacts, and for
           vulnerable groups.72

       o  High adaptive capacity does not necessarily translate into actions that reduce  vulnerability.
           For example, despite a high capacity to adapt to heat stress through relatively inexpensive
           adaptations, residents in urban areas in some parts of the world, including European cities,
           continue to  experience high levels of mortality.73    To minimize  the  risks of heat stress
           domestically, EPA  (2006) has  worked collaboratively with other government agencies to
           provide guidance to municipalities on steps they can take to reduce heat-related  morbidity
           and mortality.74
       Very high confidence            At least 9 out of 10 chance of being correct
       High confidence                About 8 out of 10 chance
       Medium confidence             About 5 out of 10 chance
       Low confidence                About 2 out of 10 chance
       Very low confidence            Less than a 1 out of 10 chance

68Adger et al. (2007), p. 720
69 ibid
70 ibid
71 Adgeretal. (2007), p. 719
72 ibid
73 ibid
74 Excessive Heat Events Guidebook (2006)
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       o   Further research is needed to monitor progress on adaptation, and to assess the direct as well
           as ancillary effects of adaptation measures.75

    4.  For any country - even one with high adaptive capacity — it is particularly difficult to reduce
       vulnerability for all segments of the population.  The most vulnerable and difficult to reach
       populations are the elderly, children and the poor.

       o   The  IPCC  states with very high confidence that "adaptive capacity is uneven across  and
           within societies." There are individuals and groups within all societies that have insufficient
           capacity to  adapt to climate change.76

    5.  More adaptation will be required to reduce  vulnerability  to  climate change.  77  Additional
       adaptation can potentially reduce, but is never expected to completely eliminate vulnerability to
       current and future climate change.

       o   According  to the IPCC, "adaptation alone is not expected to cope with  all the projected
           effects of climate change, and especially not over the long term as most impacts increase in
           magnitude." 78

    6.  A portfolio of adaptation and mitigation measures can diminish the  risks associated  with
       climate change.

       o   Even the most stringent mitigation efforts cannot avoid further impacts of climate change in
           the next few decades, which makes adaptation essential, particularly in addressing near-term
           impacts.  Unmitigated climate change would, in the long term, be likely to exceed the
           capacity of natural, managed and human systems to adapt.79
75Adgeretal. (2007) p. 737
76Adgeretal. (2007), p. 719
77Adgeretal. (2007), p. 719
78 IPCC (2007), p. 19
79 IPCC (2007), p. 20
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References for Adaptation Appendix

Adger, W.N., S. Agrawala, M.M.Q. Mirza, C. Conde, K. O'Brien, J. Pulhin, R. Pulwarty, B. Smit and K. Takahashi,
    (2007) Assessment of adaptation practices, options, constraints and capacity. Climate Change 2007: Impacts,
    Adaptation and  Vulnerability. Contribution of Working Group II to  the Fourth Assessment Report of the
    Intergovernmental Panel on Climate Change, M.L. Parry, O.F. Canziani, J.P. Palutikof, P. J. van der Linden and
    C.E. Hanson, Eds., Cambridge University Press, Cambridge, UK, 717-743.

Excessive Heat Events Guidebook. Report from the United States Environmental Protection Agency. 52 pages. June
    2006. EPA 430-B-06-005.

IPCC (2007)  Summary  for  Policymakers.  In: Climate Change  2007:  Impacts, Adaptation  and Vulnerability.
    Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate
    Change [M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson  (eds.)]. Cambridge
    University Press, Cambridge, United Kingdom and New York, NY, USA.

U.S. EPA (2008) National Water Program Strategy: Response to Climate Change. Office of Water. EPA 800-R-
    08001, September.
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Technical Support Document - Appendix B

Greenhouse Gas Emissions from Section 202(a) Source Categories

This Annex provides greenhouse gas (GHG) emissions information from Clean Air Act section
202(a) source  categories.  It includes  an overview of the respective source categories with a
description of how the emissions data from the Inventory of U.S. Greenhouse Gas Emissions and
Sinks map to  these  source  categories.  Then,  relevant emissions data  are  presented  and
comparisons are made between U.S. GHG emissions from section 202(a) source categories and
domestic and global  emissions data. To inform the Administrator's assessment, the following
types of comparisons for both the collective and individual emissions of GHGs from section
202(a) source categories are provided:

   •   as a share of total global aggregate emissions of the six GHGs;
   •   as a share of total U.S. aggregate emissions of the six GHGs; and
   •   as a share of the total global transportation emissions of the six GHGs.

In addition, for each individual GHG, the following comparisons were also calculated:

   •   as a share of total U.S. section 202(a) GHG emissions;
   •   as  a share  of U.S.  emissions  of that individual GHG,  including comparisons to the
       magnitude of emissions of that GHG from non-transport related source categories;
   •   as a share of global emissions of that individual GHG;
   •   as a share of global transport GHG emissions; and
   •   as a share of all global GHG emissions.

 (A) Overview of section 202(a) source categories

To  inform the Administrator's  cause  or  contribute  finding,  EPA analyzed historical GHG
emissions  data for  motor vehicles and  motor vehicle engines in the United States from 1990 to
2006 (the most recent year for which official EPA estimates are available).  The motor vehicles
and motor vehicle engines addressed include:

   •   Passenger cars
   •   Light-duty trucks
   •   Motorcycles
   •   Buses
   •   Medium/heavy-duty  trucks
   •   Cooling (all transportation sources)

The source of the emissions data is the Inventory of U.S. Greenhouse Gas Emissions and Sinks:
1990-2006 (USEPA  #430-R-08-002).   The  U.S. Inventory  is  organized  around the source
classification scheme  put forth by the Intergovernmental Panel  on Climate Change,  in which
emissions  from  motor vehicles and motor vehicle engines are  reported within two different
sectors:   Energy,  and Industrial Processes.   Table  TSD-B.l  describes  the  correspondence
between section 202(a) GHG emission source categories and IPCC source categories:
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Table TSD-B.l - Source categories included under section 202(a)
section 202(a) Source
Category
Passenger Cars
Light-Duty Trucks
Motorcycles
Buses
Medium/Heavy -Duty
Trucks
Cooling (all
transportation
sources)
IPCC Sector
Energy
Energy
Energy
Energy
Energy
Industrial
Processes
IPCC Source Category
lA3b (i) Cars
1 A3b (ii) Light-duty trucks
1 A3b (iv) Motorcycles
lA3b (iii) Heavy-duty trucks
and buses
lA3b (iii) Heavy-duty trucks
and buses
2F1 Refrigeration and Air
Conditioning Equipment
Greenhouse Gases
CO2, CH4, N2O
CO2, CH4, N2O
CO2, CH4, N2O
CO2, CH4, N2O
CO2, CH4, N2O
Hydrofluorocarbons
(HFCs)
Greenhouse gas emissions from aviation, pipelines, railways, and marine transport are included
in the IPCC Energy Sector under 1 A3 but are not included within section 202(a).

(B) Greenhouse gas emissions from section 202(a) source categories

(1)      Total,  combined  GHG   emissions   from   section   202(a)  source   categories
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Table TSD-B.2 presents historical emissions of all GHGs (CC>2, CH4, N2O, and HFCs) from section 202(a) source categories from
1990-2006,  in carbon dioxide  equivalent units (Tg CC^e).80  Passenger cars (39.1  percent),  light-duty trucks  (31.7 percent), and
medium/heavy-duty trucks (24.2 percent) emitted the largest shares of GHG emissions in 2006, followed by cooling (all transportation
sources) (4.2 percent), buses (0.7 percent) and motorcycles (0.1 percent). From 1990 to 2006, GHG emissions from section 202(a)
source categories grew by 35.2  percent due, in part, to increased demand for travel and the stagnation of fuel efficiency across the U.S.
vehicle fleet. Since the 1970s,  the number of highway vehicles registered in the United  States has increased faster than the  overall
population, according to the Federal Highway Administration (FHWA).81 Likewise, the number of miles driven (up 40.6 percent from
1990 to 2006) and the gallons of gasoline consumed each year in the United States have increased steadily since the 1980s, according
to the  FHWA and Energy Information Administration, respectively.82 These increases in motor  vehicle usage are the result of a
confluence of factors including population growth, economic growth, urban sprawl, low fuel prices,  and increasing popularity of sport
utility vehicles and other light-duty trucks that tend to have lower fuel efficiency.
Table TSD-B.2 - Total greenhouse gas emissions by section 202(a) source category (Tg
Section 202(a) Sources
Passenger Cars
Light-Duty Trucks
Motorcycles
Buses
Medium/Heavy-Duty Trucks
Cooling (all trans. Sources)
Total
1990
656.9
336.2
1.8
8.3
228.8
0.0
1231.9
1995
633.9
428.6
1.8
9.1
272.4
18.6
1364.4
2000
670.3
489.5
1.9
10.9
342.9
52.6
1568.1
2001
673.1
492.7
1.7
10.0
342.0
57.2
1576.8
2002
686.5
502.6
1.7
9.7
356.2
61.1
1617.9
2003
664.4
536.2
1.7
10.5
352.6
64.4
1629.7
CO2e)
2004
660.7
556.9
1.8
14.7
365.4
67.8
1667.4

2005
677.3
516.3
1.6
11.8
393.2
69.7
1670.0

2006
651.2
528.2
1.9
12.1
402.5
69.5
1665.4
Between 1990 and 2006,  GHG emissions from  passenger cars  decreased 0.9 percent, though there  was some growth in GHG
emissions from 2000 to 2002, and again from 2004 to 2005.  Emissions from light-duty trucks increased 57.1 percent from 1990-2006,
largely due to the increased use of sport-utility vehicles and other light-duty trucks.  Meanwhile, GHG emissions from heavy-duty
trucks increased 75.9 percent, reflecting the increased volume of total freight movement and an increasing share transported by trucks.
In 1990 there were no hydrofluorocarbons (HFCs) used in vehicle cooling systems. HFCs were gradually introduced into motor
  A Tg is one teragram, or one million metric tons.
81 FHWA (1996 through 2008) Highway Statistics. Federal Highway Administration, U.S. Department of
Transportation, Washington, DC. Report FHWA-PL-96-023-annual. Available online at .
82 DOE (1993 through 2008) Transportation Energy Data Book. Office of Transportation Technologies, Center for Transportation Analysis, Energy Division,
Oak Ridge National Laboratory. ORNL-5198.
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vehicle air conditioning and  refrigerating systems during the 1990s as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons
(HCFCs) started to phase out of production as required under the Montreal Protocol and Title VI of the Clean Air Act.

Table TSD-B.3 presents GHG emissions from section 202(a) source categories alongside total U.S. emissions.  The table also presents
emissions from the electricity generation and industrial sectors for comparison. In 1990, section 202(a) source categories emitted 20.0
percent of total U.S. emissions, behind the electricity generation sector (30.2 percent) and the industrial  sector (23.8 percent).  By
2006, section 202(a) source categories collectively were the second largest sector with 23.6 percent of total U.S. emissions, due both
to growth in vehicle  emissions and a decline in emissions from industry.

Table TSD-B.3 - Sectoral comparison to total US greenhouse gas emissions (Tg CC^e)
U.S. Emissions
Section 202(a) GHG emissions
Share of U.S. (%)
Electricity Sector emissions
Share of U.S. (%)
Industrial Sector emissions
Share of U.S. (%)
Total US GHG emissions
1990
1231.9
20.0%
1859.1
30.2%
1460.3
23.8%
6148.3
1995
1364.4
21.0%
1989.7
30.6%
1478.0
22.8%
6494.0
2000
1568.1
22.3%
2328.9
33.1%
1432.9
20.4%
7032.6
2001
1576.8
22.8%
2290.9
33.1%
1384.3
20.0%
6921.3
2002
1617.9
23.2%
2300.4
33.0%
1384.9
19.8%
6981.2
2003
1629.7
23.3%
2329.4
33.3%
1375.5
19.7%
6998.2
2004
1667.4
23.6%
2363.4
33.4%
1388.9
19.6%
7078.0
2005
1670.0
23.4%
2430.0
34.1%
1354.3
19.0%
7129.9
2006
1665.4
23.6%
2377.8
33.7%
1371.5
19.4%
7054.2
Table  TSD-B.4 compares total GHG emissions  from section 202(a) source categories to all U.S. GHG emissions, global GHG
emissions from the transport sector (as defined by IPCC), and total global greenhouse gas emissions from all source categories, for the
year 2005.83  Section 202(a) GHG emissions are a significantly larger share of global transport greenhouse gas emissions (28.3
percent) than the corresponding share of all U.S.  GHG emissions to the global total (18.4 percent), reflecting the relative size of the
transport sector in the U.S. compared to the global average. Section 202(a) GHG emissions were 4.3 percent of total global emissions
in 2005. The global transport sector was 15.3  percent of all global emissions in 2005.
83 The year 2005 is the most recent year for which comprehensive greenhouse gas emissions data are available for all gases, all countries, and all sources. Global
estimates are 'gross' emissions estimates and do not include removals of greenhouse gas emissions from the atmosphere by terrestrial sinks (i.e., forests and other
biomass). Global data come from the World Resources Institute's Climate Analysis Indicators Tool, which contains national data submitted by Parties to the
UNFCCC, and other independent and peer-reviewed datasets (e.g., International Energy Agency).
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Table TSD-B.4 - Comparison to global greenhouse gas emissions (Tg CC^e)

All U.S. GHG emissions
Global transport GHG emissions
All global GHG emissions
2005
7,130
5,909
38,726
Sec 202(a) Share
23.4%
28.3%
4.3%
(2) Individual GHG emissions from section 202(a) source categories

Table TSD-B.5 presents total GHG emissions from section 202(a) source categories by gas, in CC>2 equivalent units.  In 2006, CC>2
made up the largest share of emissions (93.9 percent), followed by HFCs (4.2 percent), N2O (1.8 percent) and CH4 (0.1 percent).
Since 1990, the share  of HFCs has increased (from zero  in 1990), whereas the share  of the other gases  have correspondingly
decreased.  Methane and N2O emissions have decreased in absolute terms since 1990.
Table
TSD-B.5 - Greenhouse gas emissions from section 202(a) source categories by gas (Tg CO2e)
Section 202(a) Sources
C02

CH4

N2O

HFCs

Total

Share of Sec

Share of Sec

Share of Sec

Share of Sec
GHGs

202(a) GHGs

202(a) GHGs

202(a) GHGs

202(a) GHGs

1990
1187.3
96.4%
4.2
0.34%
40.4
3.3%
0.0
0.0%
1231.9
1995
1291.9
94.7%
3.8
0.28%
50.1
3.7%
18.6
1.4%
1364.4
2000
1463.8
93.4%
2.9
0.18%
48.8
3.1%
52.6
3.4%
1568.1
2001
1470.5
93.3%
2.8
0.18%
46.4
2.9%
57.2
3.6%
1576.8
2002
1512.0
93.5%
2.4
0.15%
42.3
2.6%
61.1
3.8%
1617.9
2003
1524.2
93.5%
2.2
0.14%
38.9
2.4%
64.4
4.0%
1629.7
2004
1561.4
93.6%
2.1
0.13%
36.1
2.2%
67.8
4.1%
1667.4
2005
1565.6
93.8%
1.9
0.12%
32.7
2.0%
69.7
4.2%
1670.0
2006
1564.6
93.9%
1.8
0.11%
29.5
1.8%
69.5
4.2%
1665.4
(a) Carbon dioxide emissions from section 202(a) source categories

Carbon  dioxide is emitted  from motor vehicles and motor vehicle  engines during the fossil  fuel combustion  process.   During
combustion, the carbon (C) stored in the fuels is oxidized and emitted as CC>2 and smaller amounts of other carbon compounds,
including CH/t, carbon monoxide (CO), and non-methane volatile organic compounds (NMVOCs). These other C-containing non-
CC>2 gases are emitted as by-products of incomplete fuel combustion, but are, for the most part, eventually oxidized to CC>2 in the
atmosphere.
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As the dominant GHG emitted from motor vehicles and motor vehicle engines (93.9 percent of total emissions in 2006), CC>2 emission
trends in Table TSD-B.6 mirror those of the GHG emissions total. Carbon dioxide emissions grew by 31.8 percent between 1990 and
2006. Most of this growth occurred as a result of increased CC>2 emissions from light-duty trucks (60.5 percent) and medium/heavy-
duty trucks (76.1 percent). Emissions from passenger cars did not grow over the same time period.

Table TSD-B.6 - CC>2 emissions by section 202(a) source category (Tg
Sec. 202(a) Source Categories
Passenger Cars
Light-Duty Trucks
Motorcycles
Buses
Medium/Heavy-Duty Trucks
Cooling (all trans. Sources)
Total
1990
628.8
320.7
1.7
8.3
227.8
N/A
1187.3
1995
604.9
405.0
1.8
9.0
271.2
N/A
1291.9
2000
643.5
466.0
1.8
10.9
341.5
N/A
1463.8
2001
647.9
470.3
1.7
10.0
340.6
N/A
1470.5
2002
662.6
483.2
1.7
9.6
354.8
N/A
1512.0
2003
642.1
518.8
1.6
10.5
351.2
N/A
1524.2
2004
640.0
540.8
1.7
14.7
364.1
N/A
1561.4
2005
658.4
501.9
1.6
11.8
391.9
N/A
1565.6
2006
634.5
514.9
1.9
12.1
401.3
N/A
1564.6
Table TSD-B.7 presents CC>2 emissions from section 202(a) source categories alongside total U.S. CC>2 emissions.  The table also
presents emissions from the electricity  generation and industrial sectors for comparison.  In 1990, section 202(a) source categories
emitted 23.4 percent of total U.S. CO2 emissions, behind the electricity generation sector (36.1 percent), and ahead  of the industrial
sector (18.7 percent). By 2006, emissions from section 202(a) source categories increased to 26.2 percent of total U.S. CC>2 emissions.
Table TSD-B.7 - Sectoral comparison to total U.S. CC>2 emissions (Tg
U.S. CO2 Emissions
Section 202(a) CO2 emissions
Share of U.S. CO2(%)
Electricity Sector CO2
Share of U.S. CO2(%)
Industrial Sector CO2
Share of U.S. CO2(%)
Total U.S. CO2 emissions
1990
1187.3
23.4%
1829.7
36.1%
947.5
18.7%
5068.5
1995
1291.9
23.9%
1964.6
36.4%
977.3
18.1%
5394.2
2000
1463.8
24.6%
2310.8
38.9%
967.3
16.3%
5939.7
2001
1470.5
25.2%
2273.0
38.9%
943.2
16.1%
5846.2
C02)
2002
1512.0
25.6%
2283.0
38.6%
943.0
16.0%
5908.6

2003
1524.2
25.6%
2313.2
38.9%
948.4
15.9%
5952.7

2004
1561.4
25.9%
2346.2
38.9%
974.7
16.1%
6038.2

2005
1565.6
25.8%
2412.3
39.7%
965.3
15.9%
6074.3

2006
1564.6
26.2%
2360.3
39.4%
984.1
16.4%
5983.1
Table TSD-B.8 compares total CC>2 emissions from section 202(a) source categories to total U.S. emissions, global GHG emissions
from the transport sector (as defined by IPCC), and total global GHG emissions from all source categories, for the year 2005. Section
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202(a) CC>2 emissions are a significantly larger share  of global transport  greenhouse gas emissions (26.5   percent) than  the
corresponding share of all U.S. CC>2 emissions to the global total (22.0 percent), reflecting the relative size of the transport sector in
the U.S. compared to the global average. Section 202(a) CC>2 emissions were 4.0 percent of total global greenhouse gas emissions in
2005.

Table TSD-B.8 - Comparison to U.S. and global greenhouse gas emissions (Tg CC^e)
Global Emissions
All US GHG emissions
All global CO2 emissions
Global transport GHG emissions
All global GHG emissions
2005
7,130
27,526
5,909
38,726
Sec 202(a)
22.0%
5.7%
26.5%
4.0%
CO2 Share


(b) Methane emissions from section 202(a) source categories

Methane emissions from motor vehicles are  a  function of the CFLt  and hydrocarbon content of the  motor fuel, the amount of
hydrocarbons passing uncombusted through the engine, and any post-combustion control of hydrocarbon  emissions (such as catalytic
converters).

Table TSD-B.9 shows the trend in CH4 emissions from section 202(a) source categories since 1990, presented in carbon dioxide
equivalents.  The combustion of gasoline in passenger cars and light-duty trucks was responsible for the majority (90.8 percent) of the
CH4 emitted from section 202(a) source categories.  From 1990 to 2006, CH4 emissions decreased by 57.6  percent.

Table TSD-B.9 - CH4 emissions by section 202(a) source category (Tg CC^e)
202(a) Sources
Passenger Cars
Light-Duty Trucks
Motorcycles
Buses
Medium/Heavy-Duty Trucks
Cooling (all trans. Sources)
Total
1990
2.6
1.4
0.0
0.0
0.2
N/A
4.2
1995
2.1
1.4
0.0
0.0
0.2
N/A
3.8
2000
1.6
1.1
0.0
0.0
0.1
N/A
2.9
2001
1.5
1.1
0.0
0.0
0.1
N/A
2.8
2002
1.4
0.9
0.0
0.0
0.1
N/A
2.4
2003
1.3
0.8
0.0
0.0
0.1
N/A
2.2
2004
1.2
0.7
0.0
0.0
0.1
N/A
2.1
2005
1.1
0.7
0.0
0.0
0.1
N/A
1.9
2006
1.0
0.7
0.0
0.0
0.1
N/A
1.8
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Table TSD-B.10 presents CH4 emissions from section 202(a) source categories alongside total U.S.  CH4 emissions.  The table also
presents CH4 emissions from landfills and natural gas systems for comparison. In 2006, section 202(a) source categories emitted 0.3
percent of total U.S. CH4 emissions; landfills (22.6 percent) and natural gas systems (18.4 percent) represented a significantly larger
share.  Overall, total U.S. CH4 emissions decreased by 8.4 percent (50.8 Tg CO2e) from 1990 to 2006, in part due to efforts to reduce
emissions at individual sources such as landfills and coal mines.

Table TSD-B.10 - Sectoral comparison to total U.S. CH/i emissions (Tg CC^e)
U.S. CH4 Emissions
Section 202(a) CH4 emissions
Share of U.S. CH4(%)
Landfill CH4 emissions
Share of U.S. CH4(%)
Natural Gas CH4 emissions
Share of U.S. CH4(%)
Total U.S. CH4 emissions
1990
4.2
0.70%
149.6
24.7%
124.7
20.6%
606.1
1995
3.8
0.64%
144.0
24.1%
128.1
21.4%
598.9
2000
2.9
0.50%
120.8
21.0%
126.5
22.0%
574.3
2001
2.8
0.50%
117.6
21.0%
125.3
22.4%
558.8
2002
2.4
0.43%
120.1
21.3%
124.9
22.2%
563.5
2003
2.2
0.40%
125.6
22.5%
123.3
22.1%
559.4
2004
2.1
0.38%
122.6
22.5%
114.0
20.9%
545.6
2005
1.9
0.36%
123.7
22.9%
102.5
19.0%
539.7
2006
1.8
0.32%
125.7
22.6%
102.4
18.4%
555.3
Table TSD-B.ll compares total CH4 emissions from section 202(a) source categories to U.S. GHG emissions, global GHG emissions
from the transport sector (as defined by IPCC), and to total global  GHG emissions from all source categories, for the year 2005.
Section 202(a) CH4 emissions are a significantly smaller share of U.S., global transport, and global emissions in comparison to section
202(a) CC>2 emissions.

Table TSD-B.l 1 - Comparison to US and global greenhouse gas emissions (Tg CC^e)
Global Emissions
All U.S. GHG emissions
All global CH4 emissions
Global transport GHG emissions
All global GHG emissions
2005
7,130
6,408
5,909
38,726
Sec 202(a) CH4 Share
0.03%
0.03%
0.03%
0.005%
(c) Nitrous oxide emissions from section 202(a) source categories

Nitrous oxide (N2O) is a product of the reaction that occurs between nitrogen and oxygen during fuel combustion. Nitrous oxide
emissions from motor vehicles and motor vehicle engines  are closely  related to fuel characteristics, air-fuel  mixes, combustion
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temperatures, and the use of pollution control equipment.  For example, some types of catalytic converters installed to reduce motor
vehicle NOx, CO, and hydrocarbon emissions can promote the formation of N2O.

Table TSD-B.12 shows the trend in N2O emissions from section 202(a)  source categories since  1990, presented in carbon dioxide
equivalents. Section 202(a) emissions of N2O decreased by 26.9 percent from 1990 to 2006.  Earlier generation control technologies
initially resulted in higher N2O emissions, causing a 24.2 percent increase in N2O emissions from motor vehicles between 1990 and
1995. Improvements in later-generation emission control technologies have reduced N2O output, resulting in a 41.1 percent decrease
in N2O emissions from  1995 to 2006. Overall, N2O emissions were predominantly from gasoline-fueled passenger cars (53.0 percent)
and light-duty trucks (42.8 percent) in 2006.

Table TSD-B.12 -N2O emissions by section 202(a) source category (Tg CO2e)
202(a) Sources
Passenger Cars
Light-Duty Trucks

Motorcycles
Buses
Medium/Heavy-Duty Trucks
Cooling (all trans. Sources)
Total
1990
25.4

14.1
0.0
0.0
0.8
N/a
40.4
1995
26.9

22.1
0.0
0.0
1.0
N/A
50.1
2000
25.2

22.4
0.0
0.0
1.2
N/A
48.8
2001
23.8

21.3
0.0
0.0
1.2
N/A
46.4
2002
22.5

18.5
0.0
0.0
1.3
N/A
42.3
2003
21.0

16.6
0.0
0.0
1.3
N/A
38.9
2004
19.5

15.3
0.0
0.0
1.3
N/A
36.1
2005
17.8

13.7
0.0
0.0
1.2
N/A
32.7
2006
15.6

12.7
0.0
0.0
1.1
N/A
29.5
Table TSD-B.13 presents N2O emissions from section 202(a) source categories alongside total U.S. N2O emissions.  The table also
presents N2O emissions from agricultural soil management, and nitric acid production, for comparison.  In 2006, section 202(a) source
categories emitted 8.0 percent of total U.S. N2O emissions, making it the second largest source category.  By far the  largest source
category in the U.S. is agricultural soil management, representing  72.0  percent of total N2O emissions in  2006. The third largest
source in 2006 was nitric acid production (4.3 percent).
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Table TSD-B.13 - Sectoral comparison to total U.S. N2O emissions (Tg CC^e)
US N2O Emissions
Section 202(a) N2O emissions

Share of U.S. N2O (%)
Agricultural Soil N2O emissions
Share of U.S. N2O (%)
Nitric Acid N2O emissions
Share of U.S. N2O (%)
Total U.S. N2O emissions
1990

40.4
10.5%
269.4
70.3%
17.0
4.4%
383.4
1995

50.1
72.7%
264.8
66. 9%
18.9
4.8%
395.6
2000

48.8
72.7%
262.1
67.9%
18.6
4.8%
385.9
2001

46.4
11.8%
277.0
70.5%
15.1
3.8%
392.9
2002

42.3
11.3%
262.0
69.7%
16.4
4.3%
376.1
2003

38.9
10.9%
247.3
69.4%
15.4
4.3%
356.6
2004

36.1
10.2%
246.9
69.8%
15.2
4.3%
353.5
2005

32.7
8.8%
265.2
77.7%
15.8
4.3%
370.1
2006

29.5
8.0%
265.0
72.0%
15.6
4.3%
367.9
Table TSD-B.14 compares total N2O emissions from section 202(a) source categories to U.S. GHG emissions, global GHG emissions
from the transport sector (as defined  by IPCC), total global N2O emissions, and to total global GHG emissions from  all source
categories, for the year 2005.  Section 202(a) N2O emissions are just under 0.55 percent of global transport emissions and 0.08 percent
of all global GHG emissions.

Table TSD-B.14 - Comparison to U.S. and global greenhouse gas emissions (Tg CO2e)

All U.S. GHG emissions
All global N2O emissions
Global transport GHG emissions
All global GHG emissions
2005
7,130
3,286
5,909
38,726
Sec 202(a) N2O Share
0.46%
0.99%
0.55%
0.08%
(d) HFC emissions from section 202(a) source categories

HFCs (a term which encompasses a group of eleven related compounds) are progressively replacing CFCs and HCFCs in section
202(a) cooling and refrigeration systems as they are being phased out under the Montreal Protocol and Title VI of the Clean Air Act.84
For example, HFC-134a has become a replacement for CFC-12  in mobile air conditioning  systems.  A number of HFC blends,
containing multiple compounds, have also been introduced.  The emissions pathway can be complex, with HFCs being emitted to the
atmosphere during charging of cooling and refrigeration systems, during operation, and during decommissioning/disposal.
84
  2006 IPCC Guidelines, Volume 3, Chapter 7. Page 43.
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Table TSD-B.15 shows the trend in HFC emissions from section 202(a) source categories since 1990, presented in carbon dioxide
equivalents.  The estimates are presented as the total of all section 202(a) source categories together due to the fact that the U.S.
Inventory does not disaggregate data by vehicle mode. HFCs were not used in motor vehicles in 1990, but by 2006 emissions had
increased to 69.5 Tg CC^e. From 1995 to 2006, FIFC emission from section 202(a) source categories increased by 274%.

Table TSD-B.15 - HFC emissions by section 202(a) source category (Tg CC^e)
202 HFC Sources
Cooling & refrigerated transport
1990
0.000
1995
18.6
2000
52.6
2001
57.2
2002
61.1
2003
64.4
2004
67.8
2005
69.7
2006
69.5
Table TSD-B.16 presents FIFC emissions from section 202(a) source categories alongside total U.S. FIFC emissions.  The table also
presents HFC emissions from HCFC-22 production, and all other end-use applications of substitutes for ozone depleting substances
(ODS substitutes), for comparison.  In 2006, section 202(a) source categories emitted  55.8 percent of total U.S. HFC emissions,
making it the largest source  category.  Other applications  of ODS  substitutes (including foam blowing,  fire  protection, aerosol
propellants, solvents, and other applications) accounted for 41.2 percent.  HCFC-22 chemical production results in  by-product releases
of HFC-23, which accounted for 99 percent of HFC emissions in 1990, but declined by 2006 and now represents 11.0 percent.

Table TSD-B.16 - Sectoral comparison to total US HFC emissions (Tg
U.S. HFC Emissions
Section 202(a) HFC emissions
Share of US HFC (%)
HCFC-22 Production
Share of US HFC (%)
Other ODS Substitutes
Share of US HFC (%)
Total U.S. HFC emissions
1990
0.0
0.0%
36.4
98.6%
0.5
1.4%
36.9
1995
18.6
30.0%
33.0
53. 4%
10.3
16.6%
61.8
2000
52.6
52.5%
28.6
28.6%
18.9
18.9%
100.1
2001
57.2
58.4%
19.7
20.2%
21.0
21.4%
97.9
2002
61.1
57.5%
21.1
19.9%
24.1
22.7%
106.3
2003
64.4
61.7%
12.3
11.8%
27.7
26.6%
104.5
2004
67.8
58.2%
17.2
14.8%
31.5
27.0%
116.6
2005
69.7
57.4%
15.8
13.0%
35.9
2P.5%
121.4
2006
69.5
55.8%
13.8
11.1%
41.2
33.1%
124.5
Table TSD-B.17 compares total HFC emissions from section 202(a) source categories to U.S. GHG emissions, global GHG emissions
from the transport sector (as defined by IPCC), to total global HFC emissions, and to total global GHG emissions from all source
categories, for the year 2005.  Section 202(a) HFC emissions are just over 1 percent of global transport emissions and 0.18 percent of
all global GHG emissions, but actually make up 18.3 percent of global HFC emissions.
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Table TSD-B.17 - Comparison to US and global greenhouse gas emissions (Tg CC^e)
                                    2005            Sec 202(a) HFC Share
 All U.S. GHG emissions                 7,130           0.98%
 All global HFC emissions                381             18.3%
 Global transport GHG emissions          5,909           1.18%
 All global GHG emissions	38,726	0.18%
(e) PFC and SF6 emissions

Perfluorocarbons  (PFCs) are not emitted from motor vehicles  or motor vehicle engines in the U.S.   The main sources  of PFC
emissions in the U.S. are aluminum smelting and semiconductor manufacturing.

Similarly, sulfur hexafluoride (SFe) is not emitted from motor vehicles or motor vehicle engines in the U.S., although use of SFe for
tire inflation has been reported in other countries.85  The main sources of SF6 emissions in the U.S.  are electrical transmission and
distribution systems, and primary magnesium smelting.
85 2006 IPCC Guidelines, Volume 3, Chapter 8.
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References for Appendix B

U.S. EPA (2008) Inventory of U.S. Greenhouse Gas Emissions and Sinks:  1990 - 2006. EPA-430-R-08-005,
    Washington, DC.

WRI (2009) Climate Analysis Indicators  Tool  (CAIT)  Version 6.0.  Available  at http://cait.wri.org/.  Accessed
    February 20, 2009.
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Appendix C:  Direct Effects of Ambient GHG Concentrations on Human Health

Greenhouse gases,  at both current and projected atmospheric concentrations,  are not expected to pose
exposure risks on human respiratory systems (i.e. breathing/inhalation).  The literature supporting this
conclusion is described below.

Carbon dioxide (CO2)

The direct effects of high CO2 concentrations on human health were assessed in the EPA (2000) report,
Carbon Dioxide as a Fire Suppressant: Examining the Risks, and have also been reviewed by the IPCC
(2005) Special Report on Carbon Dioxide Capture and Storage.  At concentrations above about 2%, CO2
has a  strong effect  on respiratory physiology and  at  concentrations  above  7-10%, it  can  cause
unconsciousness and death (IPCC, 2005). Exposure studies have not revealed any adverse health effect of
chronic exposure to concentrations below  1%. At  concentrations  greater than  17 percent, loss of
controlled and purposeful activity, unconsciousness, convulsions, coma, and death occur within 1 minute
of initial inhalation of CO2  (OSHA, 1989;  CCOHS, 1990; Dalgaard  et al, 1972; CATAMA, 1953;
Lambertsen, 1971). But CO2 is a physiologically active gas and is a normal component of blood gases
(EPA,  2000).  Acute CO2 exposure of up to  1 percent and 1.5 percent by volume  is tolerated quite
comfortably (EPA, 2000b).

The ambient concentration of CO2 in the atmosphere is presently about 0.039 percent by volume (or 386
ppm).  Projected increases in CO2 concentrations from anthropogenic emissions range from 41 to 158
percent above 2005 levels (of about 380ppm)  or 535 to 983 parts per million (ppm) by 2100 (Meehl et al.,
2007) (see Section 5).  Such increases would result in  atmospheric CO2 concentrations of 0.054 to 0.098
percent by volume in 2100, which is well below published thresholds for adverse health effects.

Methane (CH4)

Methane is flammable or explosive at concentrations of 5% to 15% by volume (50,000 to 150,000 ppm)
of air (NIOSH, 1994; NRC,  2000).  At high enough concentrations, CUt is also a simple asphyxiant,
capable of displacing enough oxygen to cause death by suffocation.  Threshold limit values are not
specified because the limiting factor is the available  oxygen (NRC, 2000).  Atmospheres with oxygen
concentrations below 19.5 percent can have adverse physiological effects, and atmospheres with less than
16 percent oxygen can become life threatening (MSHA, 2007).  Methane displaces oxygen to 18% in air
when present at 14% (140,000 ppm).

When oxygen is readily available, CH4 has  little toxic effect (NRC, 2000).  In assessing  emergency
exposure limits for CH4, the  NRC (2000)  determined that an exposure  limit that presents an explosion
hazard cannot be recommended, even if it is well below a concentration that would produce toxicity.  As
such, it recommended an exposure limit of 5000 ppm  for methane (NRC, 2000).  The National Institute
for Occupational Health Safety (NIOSH, 1994) established a threshold limit value (TLV) for  methane at
1,000 ppm.

The current atmospheric concentration  of  CH^ is 1.78 ppm. The projected CH4 concentration in 2100
ranges from 1.46 ppm to 3.39 ppm by 2100, well below any recommended exposure limits (Meehl et al.,
2007).
Nitrous Oxide (N2O)

Nitrous oxide is an asphyxiant at high concentrations. At lower concentrations, exposure causes central
nervous system, cardiovascular,  hepatic  (pertaining  to the liver),  hematopoietic (pertaining  to the
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formation of blood or blood cells), and reproductive effects in humans (Hathaway et al,  1991). At a
concentration of 50 to 67 percent (500,000 to 670,000 ppm) nitrous oxide is used to induce anesthesia in
humans (Rom,  1992).

NIOSH has  established a recommended exposure limit (REL) for nitrous oxide of 25 ppm as a time-
weighted average (TWA) for the duration of the exposure (NIOSH,  1992). The American Conference of
Governmental Industrial Hygienists (ACGIH) has assigned nitrous oxide a TLV of 50 ppm as a TWA for
a normal  8-hour workday and a 40-hour workweek (ACGIH, 1994).

The NIOSH limit  is based on the risk  of reproductive  system effects  and decreases in audiovisual
performance (NIOSH, 1992). The ACGIH limit is based on the  risk of reproductive, hematological
(related to the study of the nature, function, and diseases of the blood and of blood-forming organs), and
nervous system effects (ACGIH 1994)

The current atmospheric  concentration of nitrous oxide is  0.32  ppm.  The projected nitrous oxide
concentration in 2100 ranges from 0.36 to 0.46 ppm in 2100, well below any exposure limits (Meehl et
al., 2007).

Fluorinated Gases (HFCs, PFCs, SF6)

Most fluorinated gases emitted from anthropogenic activities are released in very small quantities relative
to established thresholds for adverse health outcomes from exposure. The health effects of exposure to
one illustrative HFC gas,  one illustrative HCFC gas and SF6 are given in the context  of their current
atmospheric concentration. Chlorofluorocarbons are not included in this discussion given their phaseout
under the Montreal Protocol.

The NRC (1996) recommended a 1-hr emergency exposure  guidance level (EEGL) of 4,000  ppm for
HFC-134a.   This recommendation was based on a no-observed-adverse-effect level of 40,000 ppm in
cardiac-sensitization tests  of male beagles (NRC, 1996).  It  recommended  24-hr EEGL of 1,000 ppm
based on the fetotoxicity effects (slight retardation of skeletal ossification) observed in  rats exposed to
HFC-134a.  Finally, it recommended a 90-day CEGL of 900 ppm based on a 2-year chronic toxicity study
conducted in male  rats exposed to HFC-134a at  different concentrations for 6 hours/day, 5 days/week.
The atmospheric concentration of HFC 134a in 2003 was in the  range  of 26 to 31 parts per trillion
according to IPCC/TEAP (2005), many  orders of magnitude below EEGLs.

For HCFC-123, the end points of pharmacological or adverse effects considered for establishing an EEGL
are cardiac  sensitization, anesthesia or CNS-related effects, malignant hyperthermia, and hepatotoxicity.
According to the NRC (1996), concentration required to produce cardiac sensitization in 50% of the
animals) for HCFC-123 was determined in dog  studies to be 1.9% (19,000 ppm) for a 5-minute exposure.
The NRC recommended  that  1,900 ppm (19,000  ppm  divided by an  uncertainty  factor of  10  for
interspecies variability) should be considered the human no-observed-effect level for a 1-min exposure to
HCFC-123 on the basis of the dog cardiac-sensitization model. The concentration of HCFC-123 in 1996
was 0.03 parts per trillion according  to  IPCC/TEAP (2005), many orders of magnitude below  the
established effect level.

Sulfur  hexafluoride (SF6) is a  relatively non-toxic gas but  an asphyxiant at high concentrations.  The
NIOSH, 1997)  recommended exposure  limit is  1,000 ppm. The SF6 concentration in 2003 was around 5
parts per trillion according to IPCC/TEAP (2005), many orders of magnitude below the exposure limit.
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References for Appendix C


ACGIH (1994) 1994-1995 Threshold limit values for chemical substances and physical agents and biological
    exposure indices. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

CATAMA  (1953) Aviation  Toxicology--an Introduction to the  Subject  and  a Handbook of  Data.
    Committee on Aviation Toxicology, Aero  Medical Association.  The Blakiston  Co.: New York, NY. pp.
    6-9, 31-39,  52-55, 74-79, 110-115.

Dalgaard,  J.B., G. Dencker,  B. Fallentin, P.  Hansen,  B. Kaempe, J.  Steensberger, Wilhardt, P.  (1972)  Fatal
    poisoning and other health hazards connected with industrial fishing. Br. J. Ind. Med. 29: 307-316.

Hathaway GJ, Proctor NH, Hughes JP,  and Fischman ML (1991) Proctor and Hughes' chemical hazards of the
    workplace. 3rd ed. New York, NY: Van Nostrand Reinhold.

IPCC (2005) Special Report on Carbon Dioxide Capture and Storage. A Special Report of Working Group III of the
    Intergovernmental Panel on Climate  Change.

IPCC Technology and Economic Assessment Panel (2005) IPCC/TEAP Special Report on Safe-guarding the Ozone
    Layer and the Global Climate  System: Issues Related to  Hydrofluorocarbons and Perfluorocarbons.  Prepared
    by Working Group I and III of the  IPCC,  and the TEAP.  Edited by B. Metz, L. Kuijpers, S. Solomon, S.O.
    Andersen, O. Davidson, J. Pons, D. de Jager, T. Kestin, M. Manning, and L.A. Meyers, 488 pp., Cambridge
    University Press, Cambride, U.K., and New York, NY, USA.

Lambertsen, CJ.  (1971) "Therapeutic Gases—Oxygen, Carbon Dioxide, and Helium." Drill's Pharmacology in
    Medicine. Chapter 55, Ed. By J.R. DiPalma. McGraw-Hill Book Co.: New York, NY.

Meehl, G.A. et al. (2007) Global Climate Projections. In: Climate Change 2007:  The Physical Science  Basis.
    Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate
    Change [Solomon, S., D. Qin, M. Manning, Z.  Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L.  Miller
    (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.


Mine Safety and Health Administration  (MSH A)  (2007) The Danger of Oxygen Deficiency in  Underground Coal
    Mines.  Department  of  Labor Program Information   Bulletin   NO.  P07-05.  Internet  site located at
    http://www.msha.gov/regs/complian/PIB/2007/pib07-05.asp


NIOSH (1997) NIOSH Pocket Guide to Chemical Hazards. U.S. Department of Health and Human Services, Public
    Health Service, Centers for Disease  Control and Prevention, Washington, D.C.  NIOSH Publication no. 97-140;
    NTIS no. PB-97177604. Internet site located at http://www.cdc.gov/niosh/npg/npgd0576.html

NIOSH (1994) International Chemical Safety Cards - Methane. U.S. Department of Health and Human Services,
    Public Health Service, Centers for Disease Control and Prevention, Washington, D.C. Internet site located at
    http://www.cdc.gov/niosh/ipcsneng/neng0291.html

NIOSH (1992) Recommendations for occupational safety and health: Compendium of policy documents and
    statements. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for
    Disease Control,  National Institute for Occupational Safety and Health (NIOSH) Publication No. 92-100.

National  Research Council (NRC) (2000) Emergency and  Continuous Exposure Limits for Selected Airborne
    Contaminants, Volume 1. National Academy Press, Washington, D.C.

National Research Council (NRC)  (1996) Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-
    123. National Academy Press, Washington, D.C.
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OSHA (1989) Carbon Dioxide, Industrial Exposure and  Control Technologies for OSHA Regulated Hazardous
    Substances, Volume I of II, Substance A -1. Occupational Safety and Health Administration. Washington, DC:
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Rom, WN (1992) Environmental and occupational medicine. 2nd ed. Boston, MA: Little, Brown and Company.

U.S. EPA (2000a) Carbon Dioxide as a Fire Suppressant: Examining the Risks, EPA 430-R-00-002, May.

U.S. EPA (2000b) Carbon Dioxide as a Fire Suppressant: Examining the Risks, Appendix B - Overview of Acute
    Health Effects, EPA 430-R-00-002, May.
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