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What Climate Change
Means for Montana
Montana's climate is changing. In the past century,
most of the state has warmed about two degrees (F).
Heatwaves are becoming more common, and snow
is melting earlier in spring. Rising temperatures and
recent droughts have killed many trees by drying out
soils, increasing the risk of forest fires, or enabling
outbreaks of forest insects. In the coming decades,
the changing climate is likely to decrease the avail-
ability of water in Montana, affect agricultural yields,
and further increase the risk of wildfires.
The climate is changing because Earth is warming.
People have increased the amount of carbon dioxide
in the air by 40 percent since the late 1700s. Other
heat-trapping greenhouse gases are also increasing.
These gases have warmed the surface and lower
atmosphere of our planet about one degree during
the last 50 years. Evaporation increases as the at-
mosphere warms, which increases humidity, average
rainfall, and the frequency of heavy rainstorms in
many places—but contributes to drought in others.
Greenhouse gases are also changing the world's
oceans and ice cover. Carbon dioxide reacts with
water to form carbonic acid, so the oceans are
becoming more acidic. The surface of the ocean has
warmed about one degree during the last 80 years,
and sea level is rising at an increasing rate. Warming
is causing snow to melt earlier in spring.
Temperature change ( F):
Snowpack and Glaciers
As the climate warms, less precipitation falls as snow, and more snow
melts during winter. That decreases snowpack—the amount of snow that
accumulates over the winter. Since the 1950s, the snowpack in Montana has
been decreasing. Diminishing snowpack can shorten the season for skiing
and other forms of winter tourism and recreation. The tree line may shift, as
higher temperatures and a longer season without snow on the ground allow
subalpine fir and other high-altitude trees to grow at higher elevations. A
higher tree line would decrease the extent of alpine tundra ecosystems,
which could threaten some species.
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Snowpack, 1955-2015
Percent Change
-80 to -60
-60 to -40
-40 to -20
-5 to -20
-5 to 5
5 to 20
20 to 40
40 to 60
60 to 80
Trends in April snowpack in Montana, 1955-2013. The snowpack has declined at
most monitoring sites in Montana. Source: EPA.
More than one thousand glaciers cover about 26 square miles of mountains
in Montana, but that area is decreasing in response to rising temperatures.
Glacier National Park's glaciers receded rapidly during the last century. Sever-
al of these glaciers are likely to disappear by 2030 if current trends continue.
Areas that are no longer covered by glaciers may still accumulate snowpack,
but the snow will no longer remain year-round.
-1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5
Rising temperatures in the last century. Montana has
warned more than most of the contiguous United
States. Source: EPA, Climate Change Indicators in the
United States.
Repeat photographs of Sperry Glacier in Glacier National Park, Source: USGS.
on Elrod photo
tesy of GNP Archives

Precipitation and Water Resources
Changing the climate is likely to increase the demand for water
and make it more available. Warmer temperatures increase evapo-
ration and water use by plants. Increases in rainfall, however, are
likely to offset these losses so that soil moisture increases slightly
or remains about the same as today. More water is likely to run off
into the upper Missouri River and its tributaries.
In areas that depend on melting snow, however, the supply
of water is likely to decline. Mountain snowpacks are natural
reservoirs that collect the snow that falls during winter and release
water when the snow melts during spring and summer. Dams
capture meltwater and retain it for use later in the year. But
upstream of these dams, as the snowpack declines, less water is
available during droughts for ecosystems, water-based recreation,
and landowners who draw water directly from a natural lake or
flowing river.
Rising temperatures and changes in rainfall are likely to have both
positive and negative effects on Montana's farms and ranches,
and the net effect is unknown. Higher temperatures reduce yields
of wheat, but higher concentrations of carbon dioxide are likely to
increase yields by a similar amount. Warmer and shorter winters
may allow for a longer growing season, which could allow two
crops per year instead of one in some instances. But warmer
winters may also promote the growth of weeds and pests.
Rising carbon dioxide concentrations are likely to increase the
productivity of rangelands. Provided that the quality of forage does
not deteriorate, the higher range productivity would increase cattle
Warmer winters could also benefit ranches by reducing losses to
winter storms. During the winter of 1996-1997, for example, high
winds and heavy snow killed half of the newborn calves and
100,000 adult cows in the Northern Great Plains. But warmer
summers would at least partly offset the benefit of warmer win-
ters, because hot weather causes cows to eat less and grow more
slowly, and it can threaten their health. Over the next 70 years, the
number of days above 100°F in Montana is likely to double.
Higher temperatures and drought are likely to increase the
severity, frequency, and extent of wildfires in Montana, which
could harm property, livelihoods, and human health. On average,
about 2 percent of the land in the state has burned per decade
since 1984. Wildfire smoke pollutes the air and can increase
medical visits for respiratory and heart problems.
Firefighters battle the Taylor Creek blaze in southeastern Montana in
2012. Credit: Gerald Vickers, National Wildfire Coordinating Group.
Longer growing seasons and increased carbon dioxide concen-
trations could increase the productivity of forests, but warmer
conditions also make forests more susceptible to pests. Tempera-
ture controls the life cycle and winter mortality rates of pests such
as bark beetles, which have infested millions of acres and killed
millions of trees across the West in recent decades. With higher
winter temperatures, some pests can persist year-round, and
new pests and diseases may become established. Drought also
reduces the ability of trees to mount a defense against attacks
from beetles and other pests.
Human Health
Extremely hot and cold days can be unhealthy—even dangerous.
Certain people are especially vulnerable, including children, the
elderly, the sick, and the poor. The elderly may be particularly
prone to heat stress and other heat-related health problems,
including dehydration, cardiovascular strain, and respiratory
problems. Those with low incomes may be particularly vulnerable
if they lack air conditioning. Power failures due to severe weather
can also present risks, especially in lightly populated areas where
access to the necessary support services may be limited. While
these risks will increase as the climate becomes warmer, illnesses
and deaths due to cold weather and snow are likely to decline.
The sources of information about climate and the impacts of climate change in this publication are: the national climate assessments by the U.S. Global Change Research
Program, synthesis and assessment products by the U.S. Climate Change Science Program, assessment reports by the Intergovernmental Panel on Climate Change, and EPA's
Climate Change indicators in the United States. Mention of a particular season, location, species, or any other aspect of an impact does not imply anything about the likelihood or
importance of aspects that are not mentioned. For more information about climate change science, impacts, responses, and what you can do, visit EPA's Climate Change website
at www.epa.aov/climatechanae.