CDA United States	AugUSt2016
Environmental Protection
Agency EPA 430-F-16-007
11 91	-L Al!..	M. _ Al	
What Climate Change
Means for California
California's climate is changing. Southern California
has warmed about three degrees (F) in the last century
and all of the state is becoming warmer. Heat waves
are becoming more common, snow is melting earlier in
spring—and in southern California, less rain is falling
as well, in the coming decades, the changing climate is
likely to further decrease the supply of water, increase
the risk of wildfires, and threaten coastal development
and ecosystems.
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 one degree during
the last 80 years. Warming is causing snow to melt
earlier in spring, and mountain glaciers are retreating.
Even the great ice sheets on Greenland and Antarctica
are shrinking. Thus the sea is rising at an increasing
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 has declined in California and the
nearby states that drain into the Colorado River.
Diminishing snowpack can shorten the season for skiing and other forms of winter
tourism and recreation. The tree line may shift, as mountain hemlock 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
Water Availability
The changing climate is likely to increase the need for water but reduce the supply.
Rising temperatures increase the rate at which water evaporates into the air from
soils and surface waters. Rising temperatures also increase the rate at which
plants transpire water into the air to keep cool, so irrigated farmland would need
more water. But less water is likely to be available, because precipitation is
unlikely to increase as much as evaporation. Soils are likely to be drier, and
periods without rain are likely to become longer, making droughts more severe.
Increasing temperatures and declining rainfall in nearby states have reduced the
flow of water in the Colorado River, a key source of irrigation water in southern
Rising temperatures iri the last century.: Southern California has
warmed more than the rest of the state. Source: EPA, Climate
Change Indicators in the United States.
This 2014 photo shows the dramatic effect of a multi-year drought on Lake Oroville.
Credit: Kelly Grow, California Department of Water Resources.
Temperature change (°F):

The decline in snowpack could further limit the supply of water for some
purposes. Mountain snowpacks are natural reservoirs. They collect the
snow that falls during winter and release water when the snow melts
during spring and summer. Over the past 50 years, snowpack has been
melting earlier in the year. Dams capture most meltwater and retain it for
use later in the year. But upstream of these reservoirs, less water is
available during droughts for ecosystems, fish, water-based recreation,
and landowners who draw water directly from a flowing river.
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Sources: Esri, DeLorme, USGS, NPS, Sources:.Esri,
Snowpack, 1955-2015 Percent Change
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Colorado River Basin
Trends in April snowpack in California and the Colorado River Basin, 1955-2013,
Snowpack has decreased at most monitoring sites in California and the basin.
Source: EPA.
About 90 percent of crops harvested
in California are grown on farms that
are entirely irrigated, so a sustained
decrease in the amount of water
available for irrigation would force
farmers to either reduce the acreage
under cultivation or shift away from
the most water-intensive crops. But
even if sufficient water is available,
rising temperatures could transform
California's agriculture. Fruit trees and
grape vines need a certain number of
"chilling hours" during which temperatures are between 32° and 50°F
in the winter before they can flower. Suitable areas for growing wine
grapes are likely to shift north, and the area capable of consistently
producing grapes for the highest-quality wines is likely to shrink by more
Warming and drought threaten
economically vital California crops,
such as grapes. Credit: Caitlyn
Kennedy; NOAA
than 50 percent during the next 75 years. Chilling will be insufficient in
much of California for the types of fruit trees found in the state today. The
yields of most grain crops currently grown in the state are likely to decline
as well. Livestock may also be affected: higher temperatures cause cows
to eat less, grow more slowly, and produce less milk, and in extreme
cases, it may threaten their health.
Wildfires and Changing Landscapes
Higher temperatures and drought are likely to increase the severity,
frequency, and extent of wildfires, which could harm property, livelihoods,
and human health. On average, 4 percent of the land in California has
burned per decade since 1984. In 2003, the Old, Grand Prix, and Padua
wildfires destroyed 800 homes in southern California, forced 100,000
residents to be evacuated, and cost $1.3 billion. Wildfire smoke can reduce
air quality and increase medical visits for chest pains, respiratory prob-
lems, and heart problems.
The combination of more fires and drier conditions may expand deserts and
otherwise change parts of California's landscape. Many plants and animals
living in arid lands are already near the limits of what they
can tolerate. A warmer and drier climate would generally expand the
geographic ranges of the Sonoran, Mojave, and Great Basin deserts. 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 a changing climate. For
similar reasons, some forests may change to desert or grassland.
Human Health
Hot days can be unhealthy—even dangerous. Certain people are
especially vulnerable, including children, the elderly, the sick, and the
poor. High air temperatures can cause heat stroke and dehydration, and
affect people's cardiovascular, respiratory, and nervous systems. Higher
temperatures are amplified in urban settings where paved and other
surfaces tend to store heat. Warming can also increase the formation of
ground-level ozone, a component of smog that can contribute to
respiratory problems. EPA and the California Air Resources Board have
been working to reduce ozone concentrations. As the climate changes,
continued progress toward clean air will be more difficult.
Sea Level Rise
Sea level is likely to rise between one and four feet in the next century.
Even a 16-inch rise could threaten coastal highways, bridges, and the
San Francisco and Oakland airports. A rise of three feet would increase
the number of Californians living in places that are flooded by a 100-year
storm from about 250,000 today to about 400,000. Along some ocean
shores, homes will fall into the water as beaches, bluffs, and cliffs erode;
but along shores where seawalls protect shorefront homes from erosion,
beaches may erode up to the seawall and then vanish. The sea could also
submerge wetlands in San Francisco Bay and other estuaries, which would
harm local fisheries and potentially remove key intertidal feeding habitat
for migratory birds.
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 vmw.eDa.aov/climatechanae.