United States
Environmental Protection
Agency
Office of Policy, Planning
and Evaluation
(2111)
EPA 230-F-97-008UU
September 1997
©EPA Climate Change And Washington
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 under way. 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 enhancedby
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
Some solar radiation
is reflected by the
earth and the
k 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.
ifrared radiation is emitted
om the earth's surface
Most radiation is abs
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 businesses.
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 institu-
tional developments. Several emissions scenarios have been
developed based on differing projections of these underlying
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 since
the late 19th century. The 9 warmest years 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
1
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Global Temperature Changes (1861-1996)
0.6
0.4
-0.6
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 uncertain-
ties 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 tempera-
ture 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 Ellensburg.
Washington, has increased from 46.2°F (1900-1929 average) to
47.2°F (1966-1995 average), and precipitation has increased by
up to 20% in some areas of the state, especially in the west.
Over the next century, Washington's climate may change even
more. Based on projections given by the Intergovernmental Panel
on Climate Change and results from the United Kingdom Hadley
Centre's climate model (HadCM2), a model that has accounted
for both greenhouse gases and aerosols, by 2100 temperatures in
Washington could increase by about 5°F in winter and summer.
and by about 4°F in spring and fall (with a range of 2-9°F).
Precipitation is projected to change little in spring, summer, and
fall, and to increase by around 10% in winter.
The frequency of extreme hot days in summer is expected to
increase along with the general warming trend. It is not clear
how severe storms would change.
Climate Change Impacts
Global climate change poses risks to human health and to
terrestrial and aquatic ecosystems. Important economic resources
such as agriculture, forestry, fisheries, and water resources also
may be affected. Warmer temperatures, more severe droughts and
floods, and sea level rise could have a wide range of impacts. All
these stresses can add to existing stresses on resources caused by
other influences such as population growth, land-use changes,
and pollution.
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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Similar temperature changes have occurred in the past, but the
previous changes took place over centuries or millennia instead
of decades. The ability of some plants and animals to migrate and
adapt appears to be much slower than the predicted rate of
climate change.
Human Health
Winter-related mortality in Washington could increase if such a
warming occurs, because the frequency of air masses associated
with inclement weather is expected to increase. One study has
estimated that a 3°F warming in Seattle would increase winter-
related mortality from 15 today to about 40. The elderly, particu-
larly those living alone, are at greatest risk.
There is concern that climate change could increase concentra-
tions of ground-level ozone. For example, high temperatures.
strong sunlight, and stable air masses tend to increase urban
ozone levels. Air pollution also is made worse by increases in
natural hydrocarbons emissions during hot weather. If a warmed
climate causes increased use of air conditioners, air pollutant
emissions from power plants also will increase.
Increased emissions and accelerated atmospheric chemistry could
slow progress being made in Washington to provide healthy and
clean air. Currently, the Seattle-Tacoma area does not meet the
national health standards for ozone and paniculate matter. The
paniculate matter standard is also not met in Olympia, Spokane.
Wallula, and Yakima. Ground-level ozone has been shown to
aggravate existing respiratory illnesses such as asthma, reduce
lung function, and induce respiratory inflammation. In addition.
ambient ozone reduces agricultural crop yields and impairs
ecosystem health.
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.
At Seattle, Washington, sea level already is rising by 8 inches
per century, and it is likely to rise another 19 inches by 2100.
Washington's coastal region consists primarily of cliffs and a few
low-lying tidal flats. The Puget Sound region contains tidal flats.
river deltas with salt marshes, and swamps, as well as a heavily
modified urban shoreline around Seattle. Many marshes in this
region have been diked, drained, and converted to farmland
during the last century. Sea level rise could gradually inundate
the remaining tidal flats. Over half of these could be lost under
a 1-3 foot rise in sea level.
Possible responses to sea level rise include building walls to hold
back the sea, allowing the sea to advance and adapting to it, and
raising the land (e.g., by replenishing beach sand and/or elevating
houses and infrastructure). Each of these responses will be costly.
either in out-of-pocket costs or in lost land and structures. For
Changes In Forest Cover
Current +10°F, +13% Precipitation
Tundra
Conifer Forest
Savanna/Woodland
Shrub/Woodland
Grasslands
Arid Lands
Source: VEMAP Participants (1995); Neilson (1995)
example, the cumulative cost of sand replenishment to protect
Washington's coastline from a 20-inch sea level rise by 2100 is
estimated at $143 million to $2.3 billion.
Forests
Trees and forests are adapted to specific climate conditions, and
as climate warms, forests will change. These changes could
include changes in species, geographic extent, and health and
productivity. If conditions also become drier, the current range
and density of forests could be reduced and replaced by grass-
lands and pasture. Even a warmer and wetter climate would lead
to changes; trees that are better adapted to these conditions, such
as hemlock and sitka spruce, would thrive. Under these condi-
tions, forests could become more dense. These changes could
occur during the lifetimes of today's children, particularly if they
are accelerated by other stresses such as fire, pests, and diseases.
Some of these stresses would themselves be worsened by a
warmer and drier climate.
With changes in climate, the extent of forested areas
in Washington could change little, or they could decline by 15-
25%, primarily east of the Cascades. The uncertainties depend on
many factors, including whether soils become drier and, if so, by
how much drier. Wildfire frequency and intensity could increase
and threaten the important timber producing areas of the state. In
Washington's highly productive conifer forests, drier conditions
would favor an expansion of Douglas fir, lodgepole pine, and
ponderosa pine forests at the expense of the wet-loving hemlock
and sitka spruce along the coast. These changes could affect the
character of some of Washington's forests and the activities that
depend on them.
Water Resources
Water resources are affected by changes in precipitation as well
as by temperature, humidity, wind, and sunshine. Changes in
streamflow tend to magnify changes in precipitation. Water
resources in drier climates tend to be more sensitive to climate
changes. Because evaporation is likely to increase with warmer
climate, it could result in lower river flow and lower lake levels.
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particularly in the summer. In addition, more intense precipitation
could increase flooding. If streamflow and lake levels drop.
groundwater also could be reduced.
All of Washington to the east of the Cascade Mountains lies
within the Columbia River drainage basin, where flow is domi-
nated by spring snowmelt. The third of the state that lies to the
west of the Cascades is drained by numerous smaller streams that
flow to Puget Sound, the Pacific Ocean, or the lower Columbia.
Those streams with headwaters at high elevations, especially in
the Cascades and Olympics, are affected by winter snow and
spring snowmelt, but lower elevation streams are dominated by
winter rainfall. The seasonal pattern of flow in most streams in
the eastern part of the state, and many in the west, would be
highly susceptible to warmer temperatures. Runoff peaks would
occur earlier in the year, which could cause problems for many of
the state's reservoirs, which are small in comparison to their
inflows and therefore might not be able to supply water with the
same reliability as they do under current climatic conditions.
The reduced summer and fall flows that would accompany a
warmer climate almost certainly would result in degraded water
quality. In addition, increased snowmelt could increase winter
flooding for some westside streams. Some eastside streams.
which are now rarely affected by fall and winter flooding, also
could become susceptible to winter snowmelt flooding. On the
other hand, the susceptibility of eastside streams to spring
snowmelt floods, which now account for most large floods in
eastern Washington, most likely would decrease because of
reduced spring snow accumulations.
Agriculture
The mix of crop and livestock production in a state is influenced
by climatic conditions and water availability. As climate warms.
production patterns will 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, and other
economic sectors.
Understandably, most studies have not fully accounted for
changes in climate variability, water availability, and imperfect
responses by farmers to changing climate. Including these factors
could substantially change modeling results. Analyses based on
changes in average climate and which assume farmers effectively
adapt suggest that aggregate U.S. food production will not be
harmed, although there may be significant regional changes.
In Washington, agriculture is about a $4 billion annual industry.
two-thirds of which is crops like wheat, barley, hay, and potatoes.
About 28% of the state's farm acres is irrigated. With warmer
Changes In Agricultural Yield And Production
Yield Production
c
_n
O
Wheat Hay
Barley Potatoes
• AT = 8°F; Aprecip. = 24%
Wheat Hay
Barley Potatoes
• AT = 7°F; Aprecip. = 25%
Source: Mendelsohn and Neumann (in press); McCarl (personal
communication)
temperatures, wheat yields could increase by up to 70-90%.
Barley and hay yields could decrease by 4-14%, and potato yields
could fall by 17%. Farm income could double or triple. The
number of irrigated acres could increase. This could further stress
water supplies, which may already be lower in the summer, and
water quality could be degraded further.
Ecosystems
The primary natural features of Washington that are vulnerable to
climate change are its extensive rivers, streams, and coastal
estuaries. These environments are critical for a wide diversity of
wildlife, endangered species, and commercial and sport fisheries.
Reduced flows of headwater streams, or changes in their seasonal
flows, could reduce the amount of suitable salmon spawning
habitat. In recent years, populations of salmon and steelhead have
been reduced to less than 10% of historical levels. While these
past losses cannot be attributed to climate change, pink and chum
salmon could lose all of their habitat with climate change. Other
cold water species such as brook trout, brown trout, and mountain
whitefish could lose most of their habitat. Farther downstream.
increases in sea level and decreases in river flow could affect
estuaries, increasing salinities and decreasing tidal marsh area.
Valuable commercial shellfish communities (e.g., oysters and
clams) and duck and geese populations that utilize these flats for
habitat and feeding also may decline accordingly.
In addition, mountain ecosystems could shift upslope, reducing
habitat for many subalpine species. At lower elevations, species
now found in warmer climates may survive. For example, the
climate in eastern Washington could become warm enough to
support saguaro cactus.
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.
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