United States
Environmental Protection
United States
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What Climate Change
Means fori
August 2016
Iowa's climate is changing. Most of the state
has warmed one-half to one degree (F) in
the last century, and floods are becoming
more frequent. In the coming decades, the
state will have more extremely hot days,
which may harm public health in urban areas
and corn harvests in rural areas.
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
Temperature change (°F):
-1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5
Rising temperatures in the last century. All
regions of Iowa have warmed. Source: EPA,
Climate Change Indicators in the United
Heavy Precipitation and Flooding
Changing the climate is likely to increase the frequency of floods in Iowa. Over
the last half century, average annual precipitation in most of the Midwest has
increased by 5 to 10 percent. But rainfall during the four wettest days of the
year has increased about 35 percent, and the amount of water flowing in most
streams during the worst flood of the year has increased by more than 20
percent. During the next century, spring rainfall and average precipitation are
likely to increase, and severe rainstorms are likely to intensify. Each of these
factors will tend to further increase the risk of flooding.
Flooding of the Cedar River in
2008 damaged this section of
U.S. Highway 6 east ofAtalissa.
Credit: Iowa Department of
Mississippi and Missouri Rivers
Flooding occasionally threatens both navigation and riverfront communities,
and greater river flows could increase these threats. In April and May 2011,
a combination of heavy rainfall and melting snow caused a flood that closed
the Mississippi River to navigation and caused billions of dollars in damage
downstream. Later that spring, heavy rains and rapid snowmelt upstream
led to flooding along the Missouri River, which damaged property and closed
the river to navigation. These floods caused $85 million in direct damages
along the Missouri, with the most extensive property damage and crop loss
occurring between Sioux City and Council Bluffs.
Although springtime in Iowa is likely to be wetter, summer droughts are likely
to be more severe. Higher evaporation and lower summer rainfall are likely
to reduce river flows. The drought of 2012 narrowed navigation channels,
forced lock closures, and caused dozens of barges to run aground on the
Mississippi River, which cost the region more than $275 million.

Scientists do not know how the frequency and severity of
tornadoes will change. Rising concentrations of greenhouse
gases tend to increase humidity, and thus, atmospheric
instability, which would encourage tornadoes. But wind shear
is likely to decrease, which would discourage tornadoes.
Research is ongoing to learn whether tornadoes will be more
or less frequent in the future. Because Iowa experiences about
50 tornadoes a year, such research is closely followed by
meteorologists in the state.
Changing the climate will have favorable and harmful effects on
farming, although the net effect is unknown. Longer frost-free
growing seasons and higher concentrations of atmospheric
carbon dioxide would increase yields for many crops during an
average year. But increasingly hot summers are likely to reduce
yields of corn and possibly soybeans. Higher temperatures are
also likely to reduce livestock productivity, because heat stress
disrupts the animals' metabolism. Seventy years from now, Iowa
is likely to have 10 to 20 more days per year with temperatures
above 95°F than it has today. More severe droughts or floods
would also hurt crop yields.
Drought-stricken corn in Missouri Vaiiey in August 2012. Credit: Dave
Kosiing, USDA,
Air Pollution and Human Health
Changing the climate can harm air quality and amplify
existing threats to human health. Higher temperatures can
increase the production of ground-level ozone, a pollutant that
can cause lung and heart problems. Ozone also harms plants.
In rural Iowa, ozone levels are high enough to reduce yields of
soybeans. EPA and the Iowa Department of Natural Resources
have been working to reduce ozone concentrations. As the
climate changes, continued progress toward clean air will
become more difficult.
Climate change may also increase the length and severity of
the pollen season for allergy sufferers. For example, the rag-
weed season in the northern Great Plains and Upper Midwest is
now 10 to 21 days longer than it was in 1995, because the first
frost in fall is later.
Hot days can be unhealthy—even dangerous. High air tem-
peratures can cause heat stroke and dehydration, and affect
people's cardiovascular and nervous systems. Midwestern
cities are vulnerable to heat waves, because many houses and
apartments lack air conditioning, and urban areas are typically
warmer than their rural surroundings. In recent decades,
severe heat waves have killed hundreds of people across the
Midwest. Heat stress is expected to increase as climate change
brings hotter summer temperatures and more humidity. Certain
people are especially vulnerable, including children, the elderly,
the sick, and the poor.
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 Panei 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 atwww.epa.gov/climatechanae.