United States	AuflUSt 2016
Environmental Protection
i. Agency	EPA 430-F-16-027
What Climate Change
Means for MiSSOUli
Missouri'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 ccntuiy.
Missouri has waimed less than most of the
United States. Source: EPA, Climate Change
Indicators in the United States.
Heavy Precipitation and Flooding
Changing the climate is likely to increase the frequency of floods in Missouri. 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.
Mississippi and Missouri Rivers
Flooding occasionally threatens 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, threatened Caruthersville, and prompted evacuation of Cairo, Illinois, due
to concerns that its flood protection levees might fail. To protect Cairo, the U.S. Army
Corps of Engineers opened the Birds Point-New Madrid Floodway, which lowered the
river by flooding more than 100,000 acres of farmland in Missouri. 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.
Heavy rain led to
flooding around St. Louis
in December 2015,
including this area in
Valley Park. Credit: Cpl.
Alex Flynn, Missouri Army
National Guard.
Although springtime in Missouri is iikely 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 along the
Missouri shoreline. The resulting impact on navigation cost the region more than
$275 million. The drought of 2012-2013 also threatened municipal and industrial
water users along the Missouri River.

Scientists do not know how the frequency and severity of
tornadoes will change. Increasing concentrations of green-
house 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 Missouri experiences about
50 tornadoes a year, such research is closely followed by
meteorologists in the state.
Higher temperatures and changes in rainfall are unlikely to
substantially reduce forest cover in Missouri, although the
composition of trees in the forests may change. More droughts
would reduce forest productivity, and climate change is also
likely to increase the damage from insects and diseases. But
longer growing seasons and increased carbon dioxide
concentrations could more than offset the losses from those
factors. Forests cover about one-third of the state, dominated by
oak and hickory trees. As the climate changes, the abundance
of pines in Missouri's forests is likely to increase, while the
population of hickory trees is likely to decrease.
Changing the climate will have both harmful and beneficial
effects on farming. Seventy years from now, Missouri is likely to
have more than 25 days per year with temperatures above 95°F,
compared with 5 to 15 today. Hot weather causes cows to eat
less, produce less milk, and grow more slowly—and it could
threaten their health. Even during the next few decades, hotter
summers are likely to reduce yields of corn. But higher
concentrations of atmospheric carbon dioxide increase crop
yields, and that fertilizing effect is likely to offset the harmful
effects of heat on soybeans, assuming that adequate water is
available. On farms without irrigation, however, increasingly
severe droughts could cause more crop failures. More severe
droughts or floods would also hurt crop yields.
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 some rural
parts of Missouri, ozone levels are high enough to significantly
reduce yields of soybeans and winter wheat. EPA and the
Missouri 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 ragweed
season in Kansas City has grown 18 days longer since 1995,
because the first frost in fall is later.
A photo of a ragweed plant, a common source of allergens In Missouri.
Like many crops and pollen sources, ragweed will have a longer
growing season as temperatures rise. Stock photo.
Hot days can be unhealthy—even dangerous. High air tempera-
tures can cause heat stroke and dehydration, and affect people's
cardiovascular and nervous systems. Midwestern cities like
St. Louis 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 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 atwww.epa.gov/climatechanae.