United States
Environmental Protection
Agency
Office of Policy
(2111)
EPA 236-F-98-007b
September 1998
Climate Change And Alaska
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 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
*
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.
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. Forexample, 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 Anchorage.
Alaska, has increased 3.9°F, and over the last 41 years of avail-
able data, precipitation has increased by approximately 10% in
many parts of the state. These past trends may or may not
continue into the future.
Over the next century, climate in Alaska 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
Alaska could increase by 5°F in spring, summer, and fall (with a
range of 2-9°F), and by 10°F in winter (with a range of 4-16°F).
Precipitation is estimated to increase slightly in fall and winter
(with a range of 0-10%) and by 10% in spring and summer (with a
range of 5-15%). 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 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.
Precipitation Trends From 1900 To Present
Trends/100 years
Source: Karl et al. (1996)
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Human Health
Higher temperatures in Alaska will probably not produce condi-
tions hot enough to cause heat-related deaths. It is also not likely
that winter-related deaths will be greatly affected if warming
occurs. In urban areas, 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. Although Alaska is in compliance with current
ozone air quality standards, increased temperatures could make
remaining in compliance more difficult. Ground-level ozone is
associated with respiratory illnesses such as asthma, reduced
lung function, and respiratory inflammation.
Mosquito-borne diseases of humans have not been reported in
Alaska in the 1990s. However, if conditions become warmer and
wetter, mosquito populations could increase, thus increasing the
risk of transmission of malaria and encephalitis if these diseases
are introduced into the area. Increased runoff from heavy rainfall
could increase water-borne diseases such as giardia, crypto-
sporidia, and viral and bacterial gastroenteritides. 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 contami-
nation 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 associ-
ated flooding.
Alaska has 31,400 miles of tidally influenced shoreline. The
shoreline consists largely of fiords, bluffs, beaches, and islands.
including the extensive Aleutian chain. The Alaskan coast also
supports a wide range of wetland systems. For example, a
proposed National Estuarine Research Reserve in Kachemak Bay
Future Sea Level Rise At Adak
IUU
90
70
OU
5% Chance
50% Chance
90% Chance
^
i
-
—
2050 2100 2150
Year
Sources: Lyles et al. (1988); EPA (1995)
2200
spans nearly 400,000 acres. Much of Alaska's coast remains
undeveloped; however, more than 40 percent of the population
currently resides in the coastal city of Anchorage.
Current rates of erosion of Alaska's coastline vary widely
because of local terrain and differences in the rates of uplift, as
well as the abundance of sea ice and permafrost. In some areas.
uplift as a result of tectonic activity is rapid. On average, how-
ever, Alaska's coastline is eroding at a rate of 8 feet per year.
and this rate could increase with sea level rise.
Along much of Alaska's coast, the rate of sea level rise is nearly
equal to or less than the rate of uplift. Accounting for the effects
of climate change, sea level may rise a total of 10 inches by 2100.
although at some locations a net uplift is most likely. 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, elevating houses and
infrastructure). Each of these responses will be costly, either in
out-of-pocket costs or in lost land and structures.
Water Resources
Alaska has abundant water resources, but water is not always
available where and when it is needed. Major Alaskan rivers, the
Yukon, Kusdodwin, and Cooper, are among the 10 largest in the
United States. There are more than 3 million lakes in the state; two
principal aquifers hold large amounts of water. However, environ-
mental, legal, and technological constraints limit the use of these
supplies. Glacial-fed streams are often laden with silt, many
streams freeze and run dry during the winter, and permafrost limits
the availability of groundwater. Rapid population growth in
Anchorage, Fairbanks, and Juneau, continued development of
mineral and energy resources, and expansion of other industries
have increased water demand. In many areas, water distribution
systems are strained and there is concern that projected demands
could exceed available supplies, especially in the winter.
Runoff in the state varies widely, depending on location and
elevation, but largely results from late spring and summer melting
of snow and glacial ice. At lower elevations, late summer rains
also contribute to runoff. In a warmer climate, winter precipitation
could increase in the northern latitude and Arctic regions. At
higher latitudes and elevations, increases in precipitation could
lead to greater snowfall and snow accumulation. In other regions.
warmer winters could lead to less winter precipitation as snow
and more as rainfall. Warmer temperatures could mean earlier.
more rapid snowmelts and earlier ice breakups. This could
increase water availability in the winter, when supplies are
traditionally limited. However, river and reservoir systems that
rely on glacier or snowmelt for summer flow could find supplies
insufficient during critical periods of high demand and little
rainfall. Additionally, more rain-on-snow events or sudden winter
thaws could cause severe flooding. Higher flows and more rapid
snowmelt also could increase stream bank erosion and sediments
suspended in glacial-fed streams. Warmer temperatures and shifts
in seasonal flows could alter the productivity of fish well adapted
to current conditions.
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Warmer temperatures would lead to thawing of permafrost.
melting of glaciers, and a reduction of ice on lakes and rivers.
Thawing of the permafrost can reduce slope stability and increase
erosion and landslides, which can threaten roads and bridges and
cause local floods. Changes in permafrost also could alter the lake
and wetland ecosystems maintained above the impermeable frost
layer. Reduced ice cover could improve opportunities for water
transport, tourism, and trade. In some areas, reduced ice thick-
ness could result in less severe breakups and ice-jam flooding.
However, reduced sea ice in the Bering Sea could render coastal
areas more susceptible to erosion and inundation during severe
weather events such as storm surges.
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. 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.
With changes in climate, the extent of forested areas in Alaska
could increase as warmer temperatures extend forested areas
northward and inland. White spruce stands, usually located on
south-facing slopes, could be more sensitive to warming than the
black spruce stands found on colder, north-facing slopes. Warmer
weather could increase the likelihood of insect outbreaks and of
subsequent wildfires in the dead fuel left after such an outbreak.
If the permafrost melted, the productivity of forests could
increase, but this would also be subject to wildfires and a shift
in forest composition. The extent of these changes depends on
many factors, including whether soils become drier and, if so.
how much drier. Hotter, drier weather could increase the fre-
quency and intensity of wildfires, which could change the
composition and character of the Alaskan landscape. Warmer
and wetter conditions could also affect the character and compo-
sition of some of Alaska's forests and the activities that depend
on them.
Ecosystems
Alaska is home to many immense and mostly pristine ecosystems.
In the southern panhandle and coastal regions, western hemlock-
Sitka spruce forests are a valuable timber resource. Farther north.
the steep mountains of the Alaska Range give rise to rocky
slopes, icefields, and glaciers. Broad valleys separate peaks that
often rise to above 12,000 feet. Interrelationships among perma-
frost, surface water, fire, slope, and soil type result in diverse and
complex ecosystems, including shrub communities, bogs.
floodplains, and spruce-dominated and mixed-wood forests. At
the mouth of the Yukon and Kuskokwim rivers, an Indiana-sized
area of wetlands and tundra of the subarctic coastal plain is
one of the most important waterfowl nesting areas in North
America. Tens of thousands of lakes, ponds, and streams provide
a summer home to millions of migrant birds from six continents.
including more than half of the continental population of black
brant and most of the world's emperor geese, tundra swans, and
cackling and Pacific white-fronted geese. In the far north of the
state, the tundra of the northern arctic coastal plain stretches
from the foothills of the Brooks Range to the Arctic Ocean. Here.
many species once common farther south are still abundant.
including grizzly bears, lynx, wolverines, eagles, caribou, and
wolves. During the short arctic summer, female caribou congre-
gate in the Arctic National Wildlife Refuge in the tens of thou-
sands to give birth and raise their calves. Later in the summer.
they begin a migration that will lead them over a route longer
than that of any other terrestrial animal. The coastal plain is also
frequented by specialized arctic species found only in the polar
regions, including polar bears, arctic foxes, collared lemmings.
arctic and tundra hares, and muskoxen. The oceans around
Alaska are a rich marine resource and provide habitat for endan-
gered northern right, bowhead, sei, blue, fin, humpback, and
sperm whales.
Despite the remote and pristine nature of Alaska's ecosystems.
they stand at the forefront of potential impacts of global climate
change. Warming is projected to be greater at high latitudes than
elsewhere in the world, and with sufficient warming, tundra
ecosystems are projected to significantly decline. As recorded in
tree rings, the western Arctic has experienced a period of steady
warming since approximately the 1840s. Glacier retreat, melting
permafrost, and reductions in pack ice are all projected to
continue. These changes have serious implications for many
arctic species. Earlier springs on the arctic coastal plain could
reduce plant diversity and could disrupt food resources available
to migrating caribou. These warming-induced changes in plant
communities appear to be under way. Thawing of permafrost
could reduce caribou habitat, cause landslides and erosion, clog
salmon spawning rivers with silt, and trigger the loss of areas of
boreal forest. Boreal forests could suffer increases in the annual
area burned, drought-related dieoffs, and increased susceptibility
to insect pests such as the white pine beetle. A predicted
increase in forest fires and an eventual transition to younger
stands are of particular concern for wildlife species that make
extensive use of mature and old-growth forests, such as marten.
fisher, and caribou. The low-lying marshes of the Yukon and
Kuskokwim rivers are threatened by salinization due to sea level
rise and periodic storm surges. Marine resources also could be
heavily affected. Warming of lakes and rivers could decrease
populations of coho, sockeye, and chinook salmon in the
southern parts of their ranges. Species associated with the pack
ice, including arctic cod, polar bear, ring seal, walrus, narwhal, and
beluga whale, are estimated to experience population declines or
changes in distribution.
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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