United States
Environmental Protection
Agency
Office of Policy
(2111)
EPA 236-F-98-007h
September 1998
Climate Change And Iowa
The earth's climate is predicted to change because human
activities are altering the chemical composition of the atmosphere
through the buildup of greenhouse gases — primarily carbon
dioxide, methane, nitrous oxide, and chlorofluorocarbons. The
heat-trapping property of these greenhouse gases is undisputed.
Although there is uncertainty about exactly how and when the
earth's climate will respond to enhanced concentrations of
greenhouse gases, observations indicate that detectable changes
are underway. There most likely will be increases in temperature
and changes in precipitation, soil moisture, and sea level, which
could have adverse effects on many ecological systems, as well
as on human health and the economy.
The Climate System
Energy from the sun drives the earth's weather and climate.
Atmospheric greenhouse gases (water vapor, carbon dioxide,
and other gases) trap some of the energy from the sun, creating
a natural "greenhouse effect." Without this effect, temperatures
would be much lower than they are now, and life as known today
would not be possible. Instead, thanks to greenhouse gases, the
earth's average temperature is a more hospitable 60°F. However,
problems arise when the greenhouse effect is enhancedby
human-generated emissions of greenhouse gases.
Global warming would do more than add a few degrees to today's
average temperatures. Cold spells still would occur in winter, but
heat waves would be more common. Some places would be drier,
others wetter. Perhaps more important, more precipitation may
come in short, intense bursts (e.g., more than 2 inches of rain
in a day), which could lead to more flooding. Sea levels would
be higher than they would have been without global warming,
although the actual changes may vary from place to place
because coastal lands are themselves sinking or rising.
The Greenhouse Effect
Solar
radiation
passes
through
the clear
atmosphere
Some solar radiation
is reflected by the
earth and the
atmosphere
Some of the infrared radiation passes
through the atmosphere, and some is
absorbed and re-emitted in all directions
by greenhouse gas molecules. The effect
of this is to warm the earth's surface and
the lower atmosphere.
Source: U.S. Department of State (1992)
Emissions Of Greenhouse Gases
Since the beginning of the industrial revolution, human activities
have been adding measurably to natural background levels of
greenhouse gases. The burning of fossil fuels — coal, oil, and
natural gas — for energy is the primary source of emissions.
Energy burned to run cars and trucks, heat homes and busi-
nesses, and power factories is responsible for about 80% of
global carbon dioxide emissions, about 25% of U. S. methane
emissions, and about 20% of global nitrous oxide emissions.
Increased agriculture and deforestation, landfills, and industrial
production and mining also contribute a significant share of
emissions. In 1994, the United States emitted about one-fifth of
total global greenhouse gases.
Concentrations Of Greenhouse Gases
Since the pre-industrial era, atmospheric concentrations of carbon
dioxide have increased nearly 30%, methane concentrations have
more than doubled, and nitrous oxide concentrations have risen
by about 15%. These increases have enhanced the heat-trapping
capability of the earth's atmosphere. Sulfate aerosols, a common
air pollutant, cool the atmosphere by reflecting incoming solar
radiation. However, sulfates are short-lived and vary regionally,
so they do not offset greenhouse gas warming.
Although many greenhouse gases already are present in the
atmosphere, oceans, and vegetation, their concentrations in
the future will depend in part on present and future emissions.
Estimating future emissions is difficult, because they will depend
on demographic, economic, technological, policy, and institu-
tional developments. Several emissions scenarios have been
developed based on differing projections of these underlying
factors. Forexample, by 2100, in the absence of emissions
control policies, carbon dioxide concentrations are projected
to be 30-150% higher than today's levels.
Current Climatic Changes
Global mean surface temperatures have increased 0.6-1.2°F
between 1890 and 1996. The 9 warmestyears in this century all
have occurred in the last 14 years. Of these, 1995 was the warmest
year on record, suggesting the atmosphere has rebounded from
the temporary cooling caused by the eruption of Mt. Pinatubo in
the Philippines.
Several pieces of additional evidence consistent with warming,
such as a decrease in Northern Hemisphere snow cover, a
decrease in Arctic Sea ice, and continued melting of alpine
glaciers, have been corroborated. Globally, sea levels have risen
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Global Temperature Changes (1861-1996)
Year
Source: IPCC (1995), updated
4-10 inches over the past century, and precipitation over land has
increased slightly. The frequency of extreme rainfall events also
has increased throughout much of the United States.
A new international scientific assessment by the Intergovern-
mental Panel on Climate Change recently concluded that "the
balance of evidence suggests a discernible human influence
on global climate."
Future Climatic Changes
For a given concentration of greenhouse gases, the resulting
increase in the atmosphere's heat-trapping ability can be pre-
dicted with precision, but the resulting impact on climate is more
uncertain. The climate system is complex and dynamic, with
constant interaction between the atmosphere, land, ice, and
oceans. Further, humans have never experienced such a rapid rise
in greenhouse gases. In effect, a large and uncontrolled planet-
wide experiment is being conducted.
General circulation models are complex computer simulations that
describe the circulation of air and ocean currents and how energy
is transported within the climate system. While uncertainties
remain, these models are a powerful tool for studying climate. As
a result of continuous model improvements over the last few
decades, scientists are reasonably confident about the link
between global greenhouse gas concentrations and temperature
and about the ability of models to characterize future climate at
continental scales.
Recent model calculations suggest that the global surface temper-
ature could increase an average of 1.6-6.3°F by 2100, with signif-
icant regional variation. These temperature changes would be far
greater than recent natural fluctuations, and they would occur
significantly faster than any known changes in the last 10,000
years. The United States is projected to warm more than the
global average, especially as fewer sulfate aerosols are produced.
The models suggest that the rate of evaporation will increase as
the climate warms, which will increase average global precipita-
tion. They also suggest increased frequency of intense rainfall as
well as a marked decrease in soil moisture over some mid-
continental regions during the summer. Sea level is projected to
increase by 6-38 inches by 2100.
Calculations of regional climate change are much less reliable
than global ones, and it is unclear whether regional climate will
become more variable. The frequency and intensity of some
extreme weather of critical importance to ecological systems
(droughts, floods, frosts, cloudiness, the frequency of hot or cold
spells, and the intensity of associated fire and pest outbreaks)
could increase.
Local Climate Changes
Over the last century, the average temperature near Des Moines.
Iowa, has decreased 0.2°F, and precipitation has increased by up
to 20% in many parts of the state. These past trends may or may
not continue into the future.
Over the next century, climate in Iowa could experience
additional changes. For example, based on projections made
by the Intergovernmental Panel on Climate Change and results
from the United Kingdom Hadley Centre's climate model
(HadCM2), a model that accounts for both greenhouse gases
and aerosols, by 2100 temperatures in Iowa could increase by 2°F
in summer (with a range of 1 -4°F), 3 °F in spring (with a range of
1 -5 °F), and 4°F in fall and winter (with a range of 2-7°F). Precipi-
tation is estimated to increase by 10% in winter and spring (with
a range of 5-20%), 15% infall (with a range of 5-30%), and 20% in
summer (with a range of 10-40%). Other climate models may show
different results, especially regarding estimated changes in
precipitation. The impacts described in the sections that follow
take into account estimates from different models. The frequency
of extreme hot days in summer would increase because of the
general warming trend. It is not clear how the severity of storms
might be affected, although an increase in the frequency and
intensity of summer thunderstorms is possible.
Precipitation Trends From 1900 To Present
Trends/100 years
Source: Karl et al. (1996)
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Human Health
Higher temperatures and increased frequency of heat waves may
increase the number of heat-related deaths and the incidence of
heat-related illnesses. The elderly, particularly those living alone.
are at greatest risk. These effects have been studied only for
populations living in urban areas; however, even those in rural
areas may be susceptible.
Climate change could increase concentrations of ground-level
ozone. For example, high temperatures, strong sunlight, and
stable air masses tend to increase urban ozone levels. A 2°F
warming in the Midwest, with no other change in weather or
emissions, could increase concentrations of ozone, a major
component of smog, by as much as 8%. Although Iowa is in
compliance with current ozone air quality standards, increased
temperatures could make remaining in compliance more difficult.
Ground-level ozone is associated with respiratory illnesses such
as asthma, reduced lung function, and respiratory inflammation.
Air pollution also is made worse by increases in natural hydrocar-
bon emissions such as emissions of terpenes by trees and shrubs
during hot weather. If a warmed climate causes increased use of
air conditioners, air pollutant emissions from power plants also
will increase.
Upper and lower respiratory allergies also are influenced by
humidity. A 2°F warming and wetter conditions could increase
respiratory allergies.
Warming and other climate changes could expand the habitat
and infectivity of disease-carrying insects. Infected individuals
can bring malaria to places where it does not occur naturally.
Also, some mosquitoes in Iowa can carry malaria, and others
can carry California encephalitis, which can be lethal or cause
neurological damage. If conditions become warmer and wetter.
mosquito populations could increase, thus increasing the risk
of transmission if these diseases are introduced into the area.
Warmer temperatures could increase the incidence of Lyme
disease and other tick-borne diseases in Iowa, because popula-
tions of ticks, and their rodent hosts, could increase under
warmer temperatures and increased vegetation.
Increased runoff from heavy rainfall could increase water-borne
diseases such as giardia, cryptosporidia, and viral and bacterial
gastroenteritides. Developed countries such as the United States
should be able to minimize the impacts of these diseases through
existing disease prevention and control methods.
Water Resources
Iowa is bordered on the east by the Mississippi River and on
the west by the Missouri River. Roughly two-thirds of the state
drains to the Mississippi, and the western third drains to the
Missouri. Along the major rivers, the largest water withdrawals
are for thermoelectric power generation. In the central and
northern parts of the state, groundwater is more important
than surface water because these areas contain most of the
population, and the principal use of groundwater is for public
supply. During most years, precipitation is sufficient to
maintain streamflow, recharge aquifers, and preserve sufficient
soil moisture to support agriculture (which is primarily rainfed).
However, streamflow is highly variable, and during years with
less-than-average precipitation, surface water supplies become
critically deficient, particularly in the western and south-central
areas of the state. This situation could be exacerbated in a warmer
climate. Runoff in the state comes largely from rainfall, and to a
lesser degree from snowmelt. Warmer winter temperatures would
lead to earlier snowmelt and would increase streamflows in winter
and spring. In the summer, without large increases in precipita-
tion, higher temperatures and increased evaporation would
reduce streamflows, lake levels, and groundwater levels. Lower
streamflow and lake levels would limit important uses of the
Mississippi and Missouri River reservoirs, including navigation.
hydropower generation, recreation, wildlife conservation, and
wastewater assimilation. Water availability also would be reduced
for offstream uses such as thermoelectric power generation.
supply for a growing population, and irrigation demand. In
western Iowa, groundwater is used for irrigation during droughts
and at critical times in the growing season. Groundwater also is
used to water livestock throughout the state. Lower groundwater
levels would adversely impact these agricultural uses, as well as
public supplies. Lower flows and higher temperatures also could
degrade water quality by concentrating pollutant levels and could
impair wetlands.
In Iowa, too much rain is as much a concern as too little. Many
areas are susceptible to flooding, and the fertile soils in the
state are highly erodible. Also, many soils have little permeability.
and drainage is a problem. Surface-water quality problems are
associated with sedimentation from soil erosion and with high
concentrations of nitrates, pesticides, and nutrients from
agricultural runoff. Increased rainfall would aggravate these
problems, particularly because heavier rains are expected in a
warmer climate.
Agriculture
The mix of crop and livestock production in a state is influenced
by climatic conditions and water availability. As climate warms.
production patterns could shift northward. Increases in climate
variability could make adaptation by farmers more difficult.
Warmer climates and less soil moisture due to increased evapora-
tion may increase the need for irrigation. However, these same
conditions could decrease water supplies, which also may be
needed by natural ecosystems, urban populations, industry.
and other users.
Understandably, most studies have not fully accounted for
changes in climate variability, water availability, crop pests.
changes in air pollution such as ozone, and adaptation by farmers
to changing climate. Including these factors could change
modeling results substantially. Analyses that assume changes in
average climate and effective adaptation by farmers suggest that
aggregate U.S. food production would not be harmed, although
there may be significant regional changes.
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Changes In Agricultural Yield And Production
Dryland Yield Production
30
20
Si 10
6 0
s?
-10
-20
-30
Corn Soybeans
I AT = 9°F; Aprecip. = 4%
Corn Soybeans
AT = 8°F; Aprecip. = 17%
Sources: Mendelsohn and Neumann (in press); McCarl
(personal communication)
In Iowa, production agriculture is a $ 10 billion annual industry.
60% of which comes from livestock, mainly cattle. Very few of the
farmed acres are irrigated. The major crops in the state are corn
and soybeans. Corn yields could fall 7-23%, depending on the
extent to which temperature rises beyond the tolerance level of
the crop. Soybean yields could fall by 3% or, if changes are less
severe, could rise by 18%. Farmed acres could remain fairly
constant or could decrease by as much as 8%. Livestock and
dairy production may not be affected, unless summer tempera-
tures rise significantly and conditions become significantly drier.
Under these conditions, livestock tend to gain less weight and
pasture yields decline, limiting forage.
Forests
Trees and forests are adapted to specific climate conditions.
and as climate warms, forests will change. These changes could
include changes in species composition, geographic range, and
health and productivity. If conditions also become drier, the
current range and density of forests could be reduced and
replaced by grasslands and pasture. Even a warmer and wetter
climate could lead to changes; trees that are better adapted to
warmer conditions, such as oaks and southern pines, would
prevail. Under these conditions, forests could become more
dense. These changes could occur during the lifetimes of today's
children, particularly if the change is accelerated by other
stresses such as fire, pests, and diseases. Some of these stresses
would themselves be worsened by a warmer and drier climate.
In Iowa, less than 5% of the area is forested, mostly along rivers
and streams. With changes in climate, the extent of forested areas
in Iowa may change little or could increase by as much as 10-40%.
depending on competition from agricultural uses. The uncertain-
ties also depend on many other factors, including whether soils
become drier and, if so, how much drier. With hotter, drier weather.
southern pines gradually would replace deciduous forests in the
southern part of the state, particularly in areas with rich soils. In
areas with poorer soils, which are common in some Iowa forests.
scrub oaks of little commercial value (e.g., post oak and blackjack
oak) could increase. In contrast, warmer, wetter conditions could
expand northward the range of oak and pine forests and
riparian woodlands.
Ecosystems
Iowa lies in a zone of transition between the forested ecosystems
to the east and the Great Plains of the central United States. The
natural heritage of the state includes hardwood forests in the
south and east, the bluestem prairie in the northwest, and the elm-
ash-cottonwood forests of the Mississippi tributaries. The Prairie
Pothole Region, which extends into north-central Iowa, is a
globally important resource for waterfowl and shorebirds.
Millions of migratory birds use the Mississippi River corridor
during fall and spring migration, which is critical because of its
north-south orientation and its nearly uninterrupted habitat.
Desoto National Wildlife Refuge, for example, is a temporary
home for hundreds of thousands of snow geese and tens of
thousands of ducks. Much of the state is intensively cultivated.
and surface water systems receive substantial inputs of nutrients.
pesticides, sediments, and pollutants. As a result, populations of
fingernail clams, unionid mussels, submersed vegetation, mink.
and migratory waterfowl have declined in recent decades. Many
waterfowl populations have also declined recently; for example.
mallard, blue-winged teal, and northern pintail are at or near their
lowest numbers ever recorded. Along one of the reaches of the
Mississippi in southern Iowa, peak numbers of lesser scaup
have decreased from 300,000-500,000 in the 1970s to fewer than
25,000 today. The oak savannas of the transition zone between
the vast treeless prairies and eastern deciduous forests now
share equal billing with tallgrass prairie as one of the most
threatened plant communities in the Midwest. Historically, they
covered large parts of eastern and southern parts of the state,
but today they have all but disappeared and are a globally
endangered ecosystem. The estimated increases in temperature
and changes in precipitation due to climate change could further
stress these wildlife and plant resources.
Water and the resulting life that it brings is key to the prairie
ecosystem. The abundance of wetlands is closely tied to the
yearly variation in weather patterns, including variation in both
precipitation and temperature. This has important implications for
the shorebird migrants that funnel through the Great Plains.
Under drier conditions, wetland feeding areas are not as abun-
dant. As the quantity of suitable habitat declines, artificially high
concentrations of waterfowl may lead to increased transmission
of avian botulism and large-scale dieoffs. Species of the upland
prairie also could face problems in a changing climate. For
example, one study showed that all 23 grassland bird species
would shift their range and approximately half would decline in
range under projected climate change. Sprague's pipit and
McCown's longspur could become extinct and chestnut-collared
longspur and Baird's sparrow were highly vulnerable.
For further information about the potential impacts of climate
change, contact the Climate and Policy Assessment Division
(2174), U.S. EPA, 401 M Street SW, Washington, DC 20460, or
visit http://www. epa.gov/globalwarming/impacts.
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