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L Agency
What Climate Change
Means |(|ahO
August 2016
Idaho's climate is changing. Over the past century,
most of the state has warmed one to two degrees (F).
Snowpack is melting earlier in the year, and the flow of
meltwater into streams during summer is declining. In
the coming decades, streams will be warmer, popula-
tions of several fish species may decline, wildfires may
be more common, deserts may expand, and water may
be less available for irrigation.
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 during 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. Warming is causing snow to
melt earlier in spring.
Snowpack, Streamflows, and Water Availability
Much of the water needed for agriculture, public supplies, and other
uses comes from mountain snowpack, which melts in spring and
summer and runs off into rivers and fills reservoirs. As the climate
warms, less precipitation falls as snow, and more snow melts during
the winter, which decreases the snowpack. Since the 1950s, Idaho's
snowpack has been decreasing in most locations.
Diminishing snowpack may shorten the season for skiing and other
forms of winter tourism and recreation. The tree line may shift, as
subalpine fir and other high-altitude trees become able to grow at
higher elevations. A higher tree line would decrease the extent of
alpine tundra ecosystems, which could threaten some species.

Mountain snowpack at Galena Summit, close to one of the long-term
measuring sites shown In the map on the next page. April snowpack depth
has decreased here and at another site in the valley below.
Credit: G. Ingersoll, USGS.
Rising temperatures in the last century. The warming in Idaho
has been similar to the average warning nationwide.
Source: EPA, Climate Change Indicators in the United States.
A warming climate makes water iess available during summer. As
snowpack melts earlier, flows of fresh water in rivers and streams
increase during late winter and early spring, but decrease during
summer. This trend is likely to continue. Moreover, rising
temperatures increase the rate at which water evaporates (or
transpires) into the air from soils, plants, and surface waters, which
will further reduce the amount of water draining into streams. While
the impact on some streams may be negligible, in other streams, the
flow of water during summer may be 50 percent iess by mid-century
than it is today.
Temperature change (°F):

Sources: Esri.JDellorme,
ius&s, NPS^ S5urces:-Esri,
Trends in April snowpack, 1955-2013. The snowpack has declined at
most monitoring sites in Idaho. Source: EPA.
Drought and Wildfires
Climate change can increase the frequency and severity of fires that
burn forests, grasslands, and desert vegetation. On average, nearly
1 percent of the land in Idaho has burned per year since 1984,
making it the most heavily burned state in the nation. Changing
the climate is likely to more than double the area in the Northwest
burned by forest fires during an average year by the end of the
2151 century. Although drier soils alone increase the risk of wildfire,
many other factors also contribute.
Higher temperatures and a lack of water can also make trees more
susceptible to pests and disease, and trees damaged or killed burn
more readily than living trees. Changing the climate is likely to
increase the area of pine forests in the Northwest infested with
mountain pine beetles over the next few decades. Pine beetles and
wildfires are each likely to decrease timber harvests. Increasing
wildfires also threaten homes and pollute the air.
The combination of more fires and drier conditions may expand
deserts and otherwise change the landscape in southern Idaho.
Many plants and animals living in arid lands are already near the
limits of what they can tolerate. Higher temperatures and a drier
climate would generally extend the geographic range of the Great
Basin desert. In some cases, native vegetation may persist and
delay or prevent expansion of the desert. In other cases, fires or
livestock grazing may accelerate the conversion of grassland to
desert in response to changing climate. For similar reasons,
some forests may change to desert or grassland.
A few charred tree trunks are all that remains after a section of forest was
burned by the Motoiway Complex Fire near Syringa and Lowell in 2015.
Credit: Idaho Department of Lands.
Climate change may also pose challenges for livestock and crops.
Hot weather causes cows to eat less, grow more slowly, and
produce less milk; and in extreme cases it may threaten their
health. Higher emperatures might also decrease potato yields and
potato quality in the Northwest, Some farms may be harmed if
more hot days reduce crop yields, or if the decline in summer
streamflow reduces the water available for irrigation. Other farms
may benefit from a longer growing season and the fertilizing
effect of carbon dioxide.
Health and Vulnerable People
Climate change is likely to amplify some threats to health in Idaho.
Certain people are especially vulnerable, including children, the
elderly, the sick, and the poor.
Declining snowpack and streamflow are likely to harm aquatic
ecosystems and water-dependent economic activities. With less
melting snow to feed the streams during summer, water tempera-
tures will rise. The combination of warmer water and lower flows
would threaten salmon, steelhead, trout, and other coldwater fish.
Lower flows would also mean less hydroelectric power.
Snowpack, 1955-2015
-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
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.