United States
Environmental Protection
Agency
Office of Policy
(2111)
EPA 236-F-98-007aa
September 1998
Climate Change And Vermont
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
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. 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 Burlington.
Vermont, has increased 0.4°F, and precipitation has increased by
up to 5% in many parts of the state. These past trends may or
may not continue into the future.
Over the next century, Vermont's climate 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 climate model (HadCM2), a model that accounts
for both greenhouse gases and aerosols, by 2100 temperatures
in Vermont could increase by 4°F (with a range of 2-9°F) in spring
and 5°F (witharange of 2-10°F) in the other seasons. Precipita-
tion is projected to show little change in spring, to increase by
about 10% in summer and fall (with a range of 5-20%), and by
30% (witharange of 10-50%) in winter. 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. Although it is
not clear how the severity of storms might be affected, 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. The elderly, particularly those living
alone, are at greatest risk. These effects have been studied only
for populations living in urban areas; however, even those in
rural areas may be susceptible.
Climate change could increase concentrations of ground-level
ozone. For example, high temperatures, strong sunlight, and
stable air masses tend to increase urban ozone levels. In
New England, a 4°F warming, with no other change in weather
or emissions, could increase concentrations of ozone, a major
component of smog, by 4%. Although Vermont is in compliance
with current 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. Air pollution also
is made worse by increases in natural hydrocarbon emissions
such as emissions of terpenes by trees and shrubs during
hot weather. If a warmed climate causes increased use of air
conditioners, air pollutant emissions from power plants also
will increase. Respiratory and eye allergies increase in warm.
humid conditions.
Warmer temperatures could increase the incidence of Lyme
disease and other tick-borne diseases in Vermont, because
populations of ticks, and their rodent hosts, could increase
under warmer temperatures and increased vegetation.
Warmer winters, warmer temperatures, and heavy precipitation
also can increase harmful algal blooms in lakes and ponds.
reduce water quality, and increase outbreaks of cryptosporidiosis
and giardia.
Water Resources
The eastern portion of Vermont is drained by the Connecticut
River, which forms the border between Vermont and New
Hampshire. The western half of the state is drained by tributaries
that traverse the Green Mountains and flow into Lake Champlain
and the Hudson River. These surface waters provide water for
half of the state's population, are an important source of water for
industry and hydroelectric generation, and support recreation
uses. Winter snow accumulation and spring snowmelt strongly
affect all the state's rivers. A warmer climate would lead to an
earlier snowmelt, resulting in higher streamflows in winter and
spring and lower streamflows in summer and fall. Warmer summer
temperatures and longer summers could exacerbate water quality
problems such as excessive growth of aquatic weeds in Lake
Champlain and other lakes. Warmer water temperatures also
reduce dissolved oxygen levels, adversely affecting fish habitat.
and lower summer streamflows could reduce the ability of rivers
to assimilate waste. Changes in the timing and accumulation of
snow could affect skiing conditions in positive and negative
ways, such as the timing and length of season and snow depth.
Increased rainfall could result in localized flooding and exacerbate
levels of pesticides and fertilizers in runoff from agricultural lands.
major causes of degraded water quality in Vermont. Less rainfall.
particularly during the summer when temperatures and evapora-
tion are high, could reduce streamflow, lake levels, and ground-
water levels. This could reduce water supplies for those areas
of the state experiencing the highest rates of growth, including
Chittenden, Rutland, Washington, and Windsor counties.
Declining aquifers would also affect small municipalities and
rural populations that depend on wells.
Lower water levels in freshwater lakes such as Lake Champlain
would reduce flood damage, but shorelines could be more
susceptible to erosion from wind and rain.
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. Including these factors could
change modeling results substantially. Analyses that assume
changes in average climate and effective adaptation by farmers
suggest that aggregate U.S. food production would not be
harmed, although there may be significant regional changes.
Changes In Agricultural Yield And Production
Dryland Yield Production
Silage Hay
• AT = 7°F; Aprecip. = -3%
Silage Hay
IAT=11°F;Aprecip. =
Sources: Mendelsohn and Neumann (in press); McCarl
(personal communication)
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In Vermont, production agriculture is a $440 million annual
industry, three-fourths of which comes from livestock, mainly
dairy operations. Very few of the farmed acres are irrigated. The
major crops in the state are silage and hay. Yields of these crops
and pasture could fall by as much as 39% under severe condi-
tions as temperatures rise beyond the tolerance levels of the crop
and are combined with increased stress from decreased soil
moisture. The extent of farmed acres, however, is projected to
remain fairly constant. Estimated changes in yield vary, depend-
ing on whether land is irrigated. Livestock and dairy production
may not be affected, unless summer temperature rises signifi-
cantly and conditions become significantly drier. Under these
conditions, livestock gain less weight and pasture yields decline.
limiting forage.
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 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 warmer condi-
tions, such as oak, hickory, and pines, would prevail. 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.
Although the extent of forested areas in Vermont could change
little because of climate change, a warmer climate could change
the character of those forests. Maple-dominated hardwood
forests could give way to forests with more oaks and conifers.
species more tolerant of higher temperatures. This change would
diminish the brilliant autumn foliage as the number of maple trees
declines. The spruce-fir forests in Vermont (and other New
England states) are near the southern limit of their extent. These
forests are sensitive to climatic stresses and have experienced
significant declines in recent decades. Across the state, as much
as 30-60% of the hardwood forests could be replaced by warmer-
climate forests with a mix of pines and hardwoods. The extent and
density of the spruce and fir forests at higher altitudes and in the
north, which support a large variety of songbirds, also could be
reduced. The change in temperature also could cause maple sap
to run earlier and more quickly, thus shortening the length of the
season for gathering sap.
Changes In Forest Cover
Current +10°F, +13% Precipitation
| Conifer Forest
| Broadleaf Forest
Savanna/Woodland
Grassland
Sources: VEMAP Participants (1995); Neilson (1995)
Ecosystems
Seven endangered animals and plants are found in Vermont.
including the Indiana bat, the dwarf wedge mussel, and Jessup's
milk vetch. These animal and plant populations could be further
stressed by changes in climate and habitat. Higher-than-normal
winter temperatures could boost temperatures inside cave bat
roosting sites, which has been shown to cause higher mortality
due to increased winter body weight loss in endangered Indiana
bats (e.g., an increase of 9°F during winter hibernation has been
associated with a 42% increase in the rate of body mass loss).
The marshes of the Missisquoi River delta on the northeastern
shore of Lake Champlain support hundreds of species of water-
fowl, which depend on the water and marsh habitat. Climate
change could alter the water balance and affect the health
and range of the marshlands.
As forests change in both range and composition, the habitat
that supports the mixture of plants and animals changes. Animal
species specific to cooler conifer forests, such as spruce grouse.
gray jays, moose, and marten, could experience moderate to
severe range reductions. Waterfowl and other migratory birds
could be especially vulnerable to climate change-induced shifts in
the timing that food resources become available. If wetlands are
reduced by a drier climate or increased frequency of droughts.
waterfowl populations also could decline.
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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