rnA United States	AugUSt2016
MKU Environmental Protection
WLJ Agency	EPA 430-F-16"052
What Climate Change
Means for'"

Wyoming's climate is changing. In the past century, most
of the state has warmed by one to three degrees (F). Heat
waves 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 availability of water in Wyoming, affect agricultural yields,
and further increase the risk of wildfires.
Our climate is changing because the 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 in the last 50 years. Evaporation increases
as the atmosphere 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):
Rising temperatures in the last century. Wyoming has warmed more than
most of the contiguous United States. Source: EPA, Climate Change
Indicators in the United States.
An unnamed glacier in the Wind River Range, along with some snowpack that has
persisted into the summer. Credit: Sean D. Birkel, University of Maine.
Wyoming's mountain ranges also contain 1,500 glaciers. As the climate
warms, most of these glaciers will retreat and some could disappear
altogether. Areas that are no longer covered by glaciers may still
accumulate snowpack, but the snow will no longer remain year-round.
Snowpack and Glaciers
As the climate warms, less precipitation falls as snow, and more snow
melts during the winter. That decreases snowpack—the amount of
snow that accumulates over the winter. Since the 1950s, the snowpack
in Wyoming 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.
A	Casper
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 Wyoming, 1955-2013. The snowpack has declined at
most monitoring sites in Wyoming. Source: EPA.

Precipitation and Water Resources
The changing climate is likely to increase the need lor water
without necessarily increasing the supply. Rising temperatures
increase the rate at which water evaporates (or transpires) into
the air from soils, plants, and surface waters. Irrigated farmland
would thus need more water. But less water is likely to be
available in the Green River Basin, because precipitation is
unlikely to increase enough to make up for the additional water
lost to evaporation. In other parts of the state, annual rainfall is
likely to increase on average, but soils are likely to become drier,
and periods without rain may become longer, making droughts
more severe. In southeastern Wyoming, drier soils could lead
farmers to withdraw more water from the High Plains Aquifer,
which is already being depleted in other parts of the Great Plains.
The decline in snowpack could further limit the supply of water.
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 most meltwater and
retain it for use later in the year. But as the snowpack declines,
less water is available upstream of these dams during droughts
for ecosystems, water-based recreation, and riparian landowners
who draw water directly from a natural lake or flowing river.
Rising temperatures, drier soils, and changing water availability
are likely to present challenges for Wyoming's farms and cattle
ranches. Hot weather causes cows to eat less and grow more
slowly, and it can threaten their health. Reduced water availability
would create challenges for ranchers, as well as farmers who
irrigate crops. Although warmer and shorter winters may allow
for a longer growing season, they may also promote the growth
of weeds and pests, and shorten the dormancy for many winter
crops, which creates the potential for crop losses due to spring
Higher temperatures and drought are likely to increase the sever-
ity, frequency, and extent of wildfires in Wyoming, which could
harm property, livelihoods, and human health. On average, about
1.4 percent of the land in the state has burned per decade since
1984. Wildfire smoke pollutes the air and can increase medical
visits for chest pains, respiratory problems, and heart problems.
Cattle grazing after the 2012 Fontenelle Fire west of Big Piney. Credit: University
of Wyoming Extension.
Longer growing seasons and increased carbon dioxide concentra-
tions could increase the productivity of forests, but warmer, drier
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
By 2050, Wyoming is likely to have twice as many days above
100°F as it has today. 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 due to a lack of air
conditioning. Power failures due to severe weather can also
present risks, especially in lightly populated areas where access
to necessary support services may be limited. While these risks
will increase as the climate becomes warmer, illnesses, injuries,
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.