United States
Environmental Protection
Agency
Office of Policy
(2111)
EPA 236-F-98-007U
September 1998
©EPA Climate Change And Oregon
The earth's climate is predicted to change because human
activities are altering the chemical composition of the atmosphere
through the buildup of greenhouse gases — primarily carbon
dioxide, methane, nitrous oxide, and chlorofluorocarbons. The
heat-trapping property of these greenhouse gases is undisputed.
Although there is uncertainty about exactly how and when the
earth's climate will respond to enhanced concentrations of
greenhouse gases, observations indicate that detectable changes
are underway. There most likely will be increases in temperature
and changes in precipitation, soil moisture, and sea level, which
could have adverse effects on many ecological systems, as well
as on human health and the economy.
The Climate System
Energy from the sun drives the earth's weather and climate.
Atmospheric greenhouse gases (water vapor, carbon dioxide,
and other gases) trap some of the energy from the sun, creating
a natural "greenhouse effect." Without this effect, temperatures
would be much lower than they are now, and life as known today
would not be possible. Instead, thanks to greenhouse gases, the
earth's average temperature is a more hospitable 60°F. However,
problems arise when the greenhouse effect is enhanced by
human-generated emissions of greenhouse gases.
Global warming would do more than add a few degrees to today's
average temperatures. Cold spells still would occur in winter, but
heat waves would be more common. Some places would be drier,
others wetter. Perhaps more important, more precipitation may
come in short, intense bursts (e.g., more than 2 inches of rain
in a day), which could lead to more flooding. Sea levels would
be higher than they would have been without global warming,
although the actual changes may vary from place to place
because coastal lands are themselves sinking or rising.
The Greenhouse Effect
Solar
radiation
Some solar radiation
is reflected by the
earth and the
atmosphere
Some of the infrared radiation passes
through the atmosphere, and some is
absorbed and re-emitted in all directions
by greenhouse gas molecules. The effect
of this is to warm the earth's surface and
the lower atmosphere.
•a red radiation is'emitted
om the earth's surface
radiation is absorbed by
urface and.warms Jt
Source: U.S. Department of State (1992)
Emissions Of Greenhouse Gases
Since the beginning of the industrial revolution, human activities
have been adding measurably to natural background levels of
greenhouse gases. The burning of fossil fuels — coal, oil, and
natural gas — for energy is the primary source of emissions.
Energy burned to run cars and trucks, heat homes and busi-
nesses, and power factories is responsible for about 80% of
global carbon dioxide emissions, about 25% of U. S. methane
emissions, and about 20% of global nitrous oxide emissions.
Increased agriculture and deforestation, landfills, and industrial
production and mining also contribute a significant share of
emissions. In 1994, the United States emitted about one-fifth of
total global greenhouse gases.
Concentrations Of Greenhouse Gases
Since the pre-industrial era, atmospheric concentrations of carbon
dioxide have increased nearly 30%, methane concentrations have
more than doubled, and nitrous oxide concentrations have risen
by about 15%. These increases have enhanced the heat-trapping
capability of the earth's atmosphere. Sulfate aerosols, a common
air pollutant, cool the atmosphere by reflecting incoming solar
radiation. However, sulfates are short-lived and vary regionally,
so they do not offset greenhouse gas warming.
Although many greenhouse gases already are present in the
atmosphere, oceans, and vegetation, their concentrations in
the future will depend in part on present and future emissions.
Estimating future emissions is difficult, because they will
depend on demographic, economic, technological, policy, and
institutional developments. Several emissions scenarios have
been developed based on differing projections of these under-
lying factors. For example, by 2100, in the absence of emissions
control policies, carbon dioxide concentrations are projected
to be 30-150% higher than today's levels.
Current Climatic Changes
Global mean surface temperatures have increased 0.6-1.2°F
between 1890 and 1996. The 9 warmestyears in this century all
have occurred in the last 14 years. Of these, 1995 was the warmest
year on record, suggesting the atmosphere has rebounded from
the temporary cooling caused by the eruption of Mt. Pinatubo in
the Philippines.
Several pieces of additional evidence consistent with warming,
such as a decrease in Northern Hemisphere snow cover, a
decrease in Arctic Sea ice, and continued melting of alpine
glaciers, have been corroborated. Globally, sea levels have risen
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Global Temperature Changes (1861-1996)
Year
Source: IPCC (1995), updated
4-10 inches over the past century, and precipitation over land has
increased slightly. The frequency of extreme rainfall events also
has increased throughout much of the United States.
A new international scientific assessment by the Intergovern-
mental Panel on Climate Change recently concluded that "the
balance of evidence suggests a discernible human influence
on global climate."
Future Climatic Changes
For a given concentration of greenhouse gases, the resulting
increase in the atmosphere's heat-trapping ability can be pre-
dicted with precision, but the resulting impact on climate is more
uncertain. The climate system is complex and dynamic, with
constant interaction between the atmosphere, land, ice, and
oceans. Further, humans have never experienced such a rapid rise
in greenhouse gases. In effect, a large and uncontrolled planet-
wide experiment is being conducted.
General circulation models are complex computer simulations that
describe the circulation of air and ocean currents and how energy
is transported within the climate system. While uncertainties
remain, these models are a powerful tool for studying climate. As
a result of continuous model improvements over the last few
decades, scientists are reasonably confident about the link
between global greenhouse gas concentrations and temperature
and about the ability of models to characterize future climate at
continental scales.
Recent model calculations suggest that the global surface temper-
ature could increase an average of 1.6-6.3°F by 2100, with signif-
icant regional variation. These temperature changes would be far
greater than recent natural fluctuations, and they would occur
significantly faster than any known changes in the last 10,000
years. The United States is projected to warm more than the
global average, especially as fewer sulfate aerosols are produced.
The models suggest that the rate of evaporation will increase as
the climate warms, which will increase average global precipita-
tion. They also suggest increased frequency of intense rainfall as
well as a marked decrease in soil moisture over some mid-
continental regions during the summer. Sea level is projected to
increase by 6-38 inches by 2100.
Calculations of regional climate change are much less reliable
than global ones, and it is unclear whether regional climate will
become more variable. The frequency and intensity of some
extreme weather of critical importance to ecological systems
(droughts, floods, frosts, cloudiness, the frequency of hot or cold
spells, and the intensity of associated fire and pest outbreaks)
could increase.
Local Climate Changes
Over the last century, the average temperature in Corvallis.
Oregon, has increased 2.5°F, and precipitation has increased by
up to 20% in many parts of the state, except along the leeward
side of the Cascades where precipitation has fallen by 20%.
These past trends may or may not continue into the future.
Over the next century, climate in Oregon may change even more.
For example, based on projections made by the Intergovernmental
Panel on Climate Change and results from the United Kingdom
Hadley Centre's climate model (HadCM2), a model that accounts
for both greenhouse gases and aerosols, by 2100 temperatures in
Oregon could increase by 5°F (with a range of 2-9°F) in winter
and summer and 4°F (with a range of 2-7°F) in spring and fall.
Precipitation is estimated to increase slightly in spring (with a
range of 0-10%), decrease slightly in summer (with a range of 0 to
-10%), and increase by 15% infall and winter (with a range of 5-
25%). Other climate models may show different results, especially
regarding estimated changes in precipitation. The impacts
described in the sections that follow take into account estimates
from different models. The amount of precipitation on extreme wet
or snowy days in winter is likely to increase. The frequency of
extreme hot days in summer would increase because of the
general warming trend. It is not clear how the severity of storms
might be affected, although an increase in the frequency and
intensity of winter storms is possible.
Precipitation Trends From 1900 To Present
Trends/100 years
+20%
+10%
+5%
-5% O
-10% O
-20%
Source: Karl et al. (1996)
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Human Health
Higher temperatures and increased frequency of heat waves may
increase the number of heat-related deaths and the incidence of
heat-related illnesses. Oregon, with its occasional, intense heat
waves, may become more susceptible if its climate changes. In
Portland, heat-related deaths are estimated to increase by nearly
150% given a summer warming of 4°F (although increased air
conditioning use may not have been fully accounted for). The
elderly, especially those living alone, are at greatest risk. This
study also projects little change in winter-related deaths in
Portland if the temperature warms by 2-3°F.
Warming and other climate changes could expand the habitat and
infectivity of disease-carrying insects, thus increasing the
potential for transmission of diseases such as malaria and dengue
("break bone") fever. Warmer temperatures could increase the
incidence of Lyme disease and other tick-borne diseases in
Oregon, because populations of ticks, and their rodent hosts.
could increase under warmer temperatures and increased vegeta-
tion.
St. Louis and California encephalitis are present in California, and
some studies indicate that these diseases could move north
under a warmer climate. Western equine encephalitis has also
been found in domestic animals in Oregon. Mosquitoes can carry
these diseases, which can be lethal or cause neurological damage.
If conditions become warmer and wetter, mosquito populations
could increase, thus increasing the risk of transmission if these
diseases, as well as malaria, are introduced into the area. In-
creased runoff from heavy rainfall could increase water-borne
diseases such as giardia and cryptosporidia.
Developed countries such as the United States should be able to
minimize the impacts of these diseases through existing disease
prevention and control methods.
Coastal Areas
Sea level rise could lead to flooding of low-lying property, loss of
coastal wetlands, erosion of beaches, saltwater contamination of
drinking water, and decreased longevity of low-lying roads.
causeways, and bridges. In addition, sea level rise could increase
the vulnerability of coastal areas to storms and associated
flooding.
Oregon has a 1,400-mile tidally influenced shoreline that consists
mostly of steep slopes, pocket beaches, and small embayments.
with a few natural coastal plains. The steep, rocky cliffs that
dominate most of the coastline limit vulnerability to sea level rise.
Coastal marshes in Oregon are limited to the Tillamook and Coos
Bay regions. Under a sea level rise of 1-3 feet, the salt marshes
along these bays and harbors could be lost (although some
migration onto undeveloped lowlands could partially offset
losses).
Evidence suggests that uplift may help mitigate the effects of sea
level rise on the Oregon coast. Along much of the coast, land is
being uplifted as a result of tectonic activity at approximately 4
inches per century. However, sea level rise could reverse that
Future Sea Level rise AtYaquina
70
60
•m
- - 5% Chance
_ _ 50% Chance
90% Chance
I
i j
i
-
—
2050
Source: EPA (1995)
2100 2150
Year
2200
trend. Accounting for sea level rise from climate change, sea level
on the Oregon Coast is estimated to rise 6 inches by 2100.
Nonetheless, the rocky shore of Oregon may limit erosion, and
help protect the coastline. The cumulative cost of sand replenish-
ment to protect the coast of Oregon from a 20-inch sea level rise
by 2100 is estimated at $60-$920 million.
Water Resources
Runoff in Oregon is highly variable, and summer flows are often
low. Reservoir storage is used throughout the state to augment
summer flows with captured winter and spring runoff. Major
regulated rivers include the Columbia along the northern border.
the Snake along the northeast border, and the Willamette.
Some models for the Pacific Northwest proj ect warmer, wetter
winters and warmer, drier summers. In the mountains, warmer
winter temperatures could mean less snowfall, more winter rain.
and a faster, earlier snowmelt. More rain and greater streamflow.
particularly during the winter, could benefit hydropower produc-
tion and water supplies, but also could increase flooding in some
areas. In the rainfall-dominated rivers in the west, projected
changes result in increased winter streamflows and decreased
summer streamflows. Because of limited storage capacity, there
could be lower reservoir and water supplies in the summer and
fall. Less water would be available to reliably support important
uses such as hydropower production, fish protection, irrigation.
recreation, and water supply. Oregon is a major producer of
hydropower, and lower flows could affect its ability to meet
energy production requirements, particularly during critical low
flow periods. Provision of adequate water for fish protection is
also an important issue. In rivers such as the Columbia, instream
flow requirements are difficult to meet because of the limited
storage available to support them. Similarly, in heavily allocated
basins such as the Snake River, current irrigation demand cannot
always be met. The public also demands high lake levels in the
summer for recreation. Lower streamflows and lake levels would
exacerbate current stresses and increase competition among
water uses. Additionally, lower summer flows and higher tempera-
tures could impair water quality by concentrating pollutants and
reducing the ability of streams to assimilate wastes.
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Agriculture
The mix of crop and livestock production in a state is influenced
by climatic conditions and water availability. As climate warms.
production patterns could shift northward. Increases in climate
variability could make adaptation by farmers more difficult.
Warmer climates and less soil moisture due to increased evapora-
tion may increase the need for irrigation. However, these same
conditions could decrease water supplies, which also may be
needed by natural ecosystems, urban populations, industry, and
other users.
Understandably, most studies have not fully accounted for
changes in climate variability, water availability, crop pests.
changes in air pollution such as ozone, and adaptation by farmers
to changing climate. Analyses that assume changes in average
climate and effective adaptation by farmers suggest that aggre-
gate U.S. food production would not be harmed, although there
may be significant regional changes.
In Oregon, production agriculture is a $2.5 billion annual industry.
three-fourths of which comes from crops. Almost one-half of the
farmed acres are irrigated. The major crops in the state are wheat.
hay, and potatoes. Climate change could increase wheat yields by
2-13%. Hay and pasture yields could rise by 10%orfallby 7%,
depending on how climate changes and whether irrigation is
used. Potato yields could fall by 17% as temperatures rise beyond
the tolerance level of the crop. Farmed acres could remainfairly
constant or could decrease by as much as 23%.
Forests
Trees and forests are adapted to specific climate conditions, and
as climate warms, forests will change. These changes could
include changes in species composition, geographic range, and
health and productivity. If conditions also become drier, the
current range and density of forests could be reduced and
replaced by grasslands and pasture (or in some forests lead to
changes in the types of trees that flourish). Even a warmer and
wetter climate could lead to changes; trees that are better adapted
to these conditions, such as hemlock and sitka spruce, would
thrive. Under these conditions, forests could become more dense.
These changes could occur during the lifetimes of today's
children, particularly if the change is accelerated by other
stresses such as fire, pests, and diseases. Some of these stresses
would themselves be worsened by a warmer and drier climate.
Commercial timber production could also be affected by resulting
changes in growth rates, plantation acreage and management,
and market conditions.
With changes in climate, the extent of forested areas in Oregon
could change little, orthey could decline by 15-25%, primarily
east of the Cascades. The uncertainties depend on many factors.
including whether soils become drier and, if so, how much drier.
Hotter, drier weather could increase the frequency and intensity
of wildfires, threatening the important timber-producing areas of
the state. In the state's highly productive conifer forests, drier
conditions would favor Douglas fir, lodgepole pine, and ponde-
rosa pine forests at the expense of the wet-loving hemlock and
Changes In Agricultural Yield And Production
Irrigated Yield Production
c
(0
6
Wheat Hay Potatoes Wheat Hay Potatoes
• AT = 8°F; Aprecip. = 22% • AT = 6°F; Aprecip. = 24%
Sources: Mendelsohn and Neumann (in press); McCarl
(personal communication)
sitka spruce along the coast. Warmer conditions could increase
the elevation of the timberline, resulting in a reduction or the
disappearance of alpine tundra and its unique (and in some cases
already endangered) species. These changes could affect the
character of Oregon forests and the activities that depend on
them.
Ecosystems
Lower streamflow in the hot summer months would have negative
consequences for fish populations in Oregon waters, which are
already under pressure from dams and other human disturbances.
Less summer and fall runoff could affect salmon migration and
spawning. More flooding and winter runoff could alter sedimenta-
tion processes in rivers and streams, perhaps harming fish habitat
and decreasing egg-smolt survival. Warmer water temperatures
affect dissolved oxygen concentrations, which could decrease
the survival rate, reproduction, and growth of certain fish.
perhaps favoring the increased range expansion of exotic species
at the expense of native species. Changing aquatic ecosystem
conditions could result in a general northward shift of species
distributions. Populations at the extremes of their range will be
those most susceptible to change.
As low-lying coastal areas are gradually squeezed between rising
sea levels and coastal development, a permanent loss of terres-
trial coastal habitats is expected. Changes in offshore upwelling
could cause changes in nutrient supplies, which could have
adverse impacts for anadromous fish such as salmon. The
rangelands of the Great Basin are already imperiled by the
expansion of non-native weedy species such as European
cheatgrass. Climate change could exacerbate such threats.
because opportunistic non-native species are well-suited to take
advantage of ecosystem disturbances caused by warming
temperatures, such as increases in the frequency and severity of
wildfires.
For further information about the potential impacts of climate
change, contact the Climate and Policy Assessment Division
(2174), U.S. EPA, 401 M Street SW, Washington, DC 20460, or
visit http://www. epa.gov/globalwarming/impacts.
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