United States
Environmental Projection
Agency """"• *^
, Off ice of Policy
(2111)
-——'•EPA 236-F-98-U07n
September 1998
&EPA Climate Change And Nebraska
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 under way. 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 enhanced by
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 akeady 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
institutional developments. Several emissions scenarios have
been developed based on differing projections of these under-
lying factors. For example, 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 warmest years 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)
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
Z
:z
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 ofl.6-6.3°Fby2100, 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 Lincoln,
Nebraska, has decreased 0.2°F, and precipitation has increased by
up to 10% in many parts of the state, except in the far western
areas where precipitation has fallen by nearly 20%. These past
trends may or may not continue into the future.
Over the next century, climate in Nebraska 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 Nebraska could increase by 3°F in spring
and summer (with a range of 1 -6°F) and 4°F in fall and winter (with
a range of 2-7°F). Precipitation is estimated to increase by 10%
(with a range of 5-20%) in spring, summer, and fall, and 15% in
winter (with a range of 5-30%). The amount of precipitation on
extreme wet or snowy days in winter is likely to increase. 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 winter storms is possible.
Precipitation Trends From 1900 To Present
Trends/1 00 years
+20%
+10% £
+5% •
-5% O
-10% O
-20%
O
O
Source: Karl etal. (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, especially those living alone,
are at greatest risk. Nebraska, with its irregular, intense heat
waves, could be susceptible. 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 Nebraska 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 hydro-
carbon 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, thus increasing the
potential for transmission of diseases such as malaria and
dengue ("break bone") fever. Infected individuals can bring
malaria to places where it does not occur naturally. Also, some
mosquitoes in Nebraska can carry western equine 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 Nebraska, because
populations of ticks, and their rodent hosts, could increase
under warmer temperatures and increased shrub and woodland
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
Nebraska relies on both surface and groundwater to meet its
water needs. Agricultural irrigation, which depends heavily on
groundwater, is the largest user of water. Thick aquifer systems
such as the High Plains, or Ogallala, aquifer underlie most regions
of the state. The Missouri River and its major tributaries, the
Platte, the Republican, and the Niobrara, drain much of the state.
However, rainfall and runoff are highly variable, and water can be
scarce in some regions and in some years. Runoff in the state
comes primarily from spring snowmelt, much of which originates
in Colorado and Wyoming, and from summer and spring thunder-
storms. A warmer climate would lead to earlier spring snowmelt,
resulting hi high streamflows in winter and spring. In the summer,
without large increases in precipitation, higher temperatures and
increased evaporation would reduce streamflows and lake levels.
Groundwater levels also could be reduced by lower spring and
summer recharge. For a doubling in CO2 levels, some studies
show a 6-34% reduction in inflow into the Missouri River system.
Drier summer conditions could severely affect the state's agricul-
tural economic base. Under current conditions, two consecutive
dry months in the summer can cause dryland crop failures. Under
climate change, increased demand and reduced water availability
in the summer also could increase competition between irrigation
and wildlife habitat needs, such as maintaining critical habitat for
migratory waterfowl in the Central flyway along the Platte River
valley. Lower streamflows could compromise important uses of
Missouri River reservoirs, including hydropower generation,
navigation, municipal-industrial supply, fish and wildlife habitat,
and recreation. Groundwater levels, which are declining in the
intensively developed areas throughout the state, could be
reduced further. The wetlands in Nebraska, which include shallow
lakes and wet meadows in the Sand Hills region, rainwater basins
in the southeast, and marshes along major rivers, also could be
impaired by lower summer flows and water levels.
More rain would ease competition for available supplies, but it
also could increase flooding. The North Platte, South Platte, and
Platte rivers are vulnerable to floods from melting snow, and small
streams can experience flash floods caused by intense summer
thunderstorms. In a warmer climate, heavier rains are expected
and flash floods could occur more frequently. Higher rainfall rates
also could increase erosion and exacerbate levels of pollution
from runoff. Leaching of nitrogen fertilizers into groundwater
and contamination of surface waters from agricultural runoff
are primary water quality concerns in Nebraska.
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
I
5
o
80
70
60
50
40
30
20
10
0
-10
•20
Corn Soybeans Hay
• AT = 9°F; Aprecip. = 2%
Corn Soybeans Hay
I AT = 8°F; Aprecip. = 11%
Sources: Mendelsohn and Neumann (in press); McCarl
(personal communication)
In Nebraska, production agriculture is a $9 billion annual industry,
60% of which comes from livestock, mainly cattle. Almost 40% of
the farmed acres are irrigated. The major crops in the state are
corn, soybeans, and hay. Climate change could reduce corn
yields by about 13% as temperature rises beyond the tolerance
level of the crop. Hay and pasture yields could increase 2-19%,
and soybean yields could increase by about 30%. Farmed acres
could remain fairly constant or could increase by 28%. Livestock
and dairy production may not be affected, unless summer
temperatures rise significantly and conditions become signifi-
cantly 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
wanner 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.
With changes in climate, the extent of forested areas in Nebraska
could change little or decline by as much as 20-50%. The uncer-
tainties depend on many factors, including whether soils become
drier and, if so, how much drier. Hotter, drier weather could
increase the frequency and intensity of wildfires, whereas
increased rainfall could reduce their severity. In areas with richer
soils, the range and density of southern pines could increase.
Grasslands and savanna eventually could replace many of the
forests and woodlands in eastern Nebraska. These changes
would significantly affect the character of eastern Nebraska
forests and woodlands.
Ecosystems
Nebraska stands at the transition between the eastern
deciduous forests, the tallgrass prairie, and the shortgrass
prairie. The oak-hickory forests of the eastern portion of the
state also extend into the northern floodplain forests along major
tributaries of the Missouri River. Important prairie ecosystems
from east to west are bluestem, wheatgrass-bluestem-
needlegrass, sandsage-bluestem, and grama-buffalo grass. The
Nebraska Sandhills prairie in the northeastern portion of the state
is one of the largest contiguous dune areas in the Western
Hemisphere. Many of the native ecosystems of the state are some
of the most critically endangered of the world's ecosystems. A
tallying of known oak savanna sites from Missouri northward in
1985 found only 6,600 acres, some 0.02% of the estimated original
coverage. Similarly, less than 1% of the original grasslands of
prairie ecosystems remains undisturbed by human activities.
These reductions have contributed to the state-wide endanger-
ment of several animal and plant species, including the black-
footed ferret, swift fox, and blow-out penstemon. During the last
25 years, populations of 10 endemic grassland bird species have
declined, and 14 of 20 species that evolved primarily on the
Great Plains declined similarly during this period.
Agricultural development and resultant nutrient, pesticide,
sediment, and pollutant input levels have possibly exceeded the
assimilative capacity of the Upper Missouri watershed. In recent
decades, populations of fingernail clams, unionid mussels,
submersed vegetation, migratory waterfowl, mink and otter have
decreased along extensive reaches of the upper river. As a result,
piping plover and interior least tern are endangered, and several
prairie fishes that were once widespread and abundant are now
threatened.
Wetlands used by the millions of waterfowl that migrate along the
Mississippi corridor have also been reduced, and populations of
mallard, blue-winged teal, and northern pintail are at or near their
lowest numbers ever recorded. An increased number of invasive
weed species, greater pest outbreaks, increased rates of aquifer
use, and loss of wetlands for waterfowl could result from in-
creased temperatures. One study of potential climate change
impacts on a typical small prairie wetland showed that drier
conditions resulted in less open water and greater vegetative
cover. This would have significant negative implications for
waterfowl populations because of the disproportionate impor-
tance of small prairie potholes and wetland extent for breeding
bird density, diversity, and reproduction. As the quantity of
suitable habitat declines, artificially high densities of waterfowl
could lead to increased transmission of avian botulism and large-
scale dieoffs.
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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