EPA's
GUIDE to
Answers to commonly
asked questions.
What individuals can
do to help reduce
the risks.
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Climate Change...
DO YOUR FART
You can save up to 40 percent in energy costs by
purchasing energy-efficient home products.
use of alternative Eielvehiclisi-
When buying or building a new house, an energy-
efficient model gives, quality and comfort as well as
lower mondily costs.
S^^
Buy products that feature reusable, recyclable, or
reduced packaging to save the energy required to
make new containers, and to reduce methane
emissions from landfills.
iEB^^
When buying a car, purchase a fuel-efficient
vehicle—one that gets'more miles to the gallon
than your current vehicle.
Consider transportation alternatives such
as mass transit, carpooling, bicycling, and
telecommuting.
Insulate, caulk windows and doors, and
tune up your furnace and air conditioner.
sg^^
Encourage your local utility to do its part by
offering energy from clean sources such as landfill
gas recovery, high-efficiency natural gas-fired power
plants, or renewables such as solar and wind.
Your company or school can save money by
upgrading its buildings to be energy-efficient,
joining climate-friendly programs, and buying
energy-efficient office equipment.
Trees absorb carbon dioxide, a greenhouse gas,
from the air. Join family members, neighbors, and
community service groups in planting trees in your
yard, along roadways, and in parks.
Let friends and family know about these practical,
energy-saving steps they can take to save money
while protecting the environment.
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ne of the most important
environmental issues facing the world
today is climate change. The Earth's surface
is becoming warmer, and evidence is
mounting that human activities are likely
contributing to the warming trend. Still,
uncertainties exist about exactly how
much of the warming is due to human
activities, whether recent temperature.
trends are truly outside the range of natural
climate variability, and the effect that
warming could have on our climate, lives,
and habitat. This brochure addresses some
commonly asked questions about climate
change. It also offers ideas, about what
individuals and communities can do to
help reduce the risk of climate change.
What Is Global Warming?
Global warming refers to any increased heating in the lower atmosphere
(at and near the Earth's surface) associated with increased concentrations
of heat-trapping greenhouse gases such .as carbon dioxide. Such heating
has recently been detected in our lower atmosphere. The rate and magni-
tude of the resultant warming at the Earth's surface appears to exceed that
of any natural warming that has occurred in at least the last thousand
years. Some portion of this warming is now thought to be the likely result
of a human-induced increase in greenhouse gas emissions.
What Is the Greenhouse Effect and How
Does It Relate to Global Warming?
The greenhouse effect is a natural process, in which heat is blocked or
slowed from escaping directly into space by greenhouse gases. Without a
natural greenhouse effect, the Earth would be too cold to support life as
we know it.
Since the Industrial Revolution, concentrations of greenhouse gases such
as carbon dioxide and methane have been increasing in the atmosphere,
enhancing the natural greenhouse effect. Most of these additional green-
house gases originate from the burning of fossil fuels such as coal, natural
gas, oil, and gasoline to power our cars, factories, utilities, and appliances.
Energy from the sun enters the
Earth's atmosphere mainly in
the form of visible light.
Some escapes
back into space
What Is Climate Change?
We all recognize weather changes: a thunderstorm interrupting a
mostly sunny day or a sudden drop in temperature in the wake of a
cold front. Weather can change rapidly and noticeably in minutes.
Climate change, on the other hand, refers to the average change in
weather conditions over long periods of time, typically decades to
centuries or longer. Examples of indications of climate change
might include observations that more snow fell in your hometown
20 years ago than it does today, or that it was warmer when
dinosaurs roamed the planet around 100 million years ago and
colder during periodic ice ages.
According to scientific studies, large climate changes pre-dating
the Industrial Revolution (circa 1750) resulted from natural causes
such as changes in solar radiation and volcanic eruptions. But since
then, human activities have significantly altered the concentrations
of many climate-regulating gases and particles in the atmosphere.
Greenhouse gases absorb infrared
radiation (in the form of heat) and
re-radiate heat energy out to jpace
and back toward the surface of the
Earth, resulting in a warming at or
near the surface of the Earth.
Some is trapped by
heat-trapping or
greenhouse gases
It is very likely' that emissions of
heat-trapping greenhouse gases
have contributed to the warming
temperature trend observed over the
past century. Unless steps are taken to
stabilize or reduce net emissions of
greenhouse gases, atmospheric concen-
trations of these gases will very likely
continue to increase, with potential long-
term effects on people, plants, and animals.
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What Are the Different Greenhouse Gases?
.Water vapor, the most abundant greenhouse gas in the atmosphere,
occurs naturally. Of the remaining greenhouse gases, carbon dioxide,
methane, nitrous oxide, and tropospheric ozone occur naturally and also
are the byproducts of human activities, while fluorinated compounds are
almost exclusively man-made. Carbon dioxide is by far the most abundant
of the human-produced greenhouse gases—all of which have increased
significantly during the Industrial Era.
Changes of Greenhouse Gas Concentrations
During the Industrial Era
Greenhouse
Gas
Carbon
Dioxide
Methane
Nitrous
Oxide
Fluorinated
Compounds
Tropospheric
Ozone
Concentration
Increase
Since 1750
31%
• ' 151%
17%
Emissions began
20th Century
36%
Human
Contribution
to Increase
Almost
All
Over
Half
About
One-third
Almost
All
Almost
All
•Primary Sources ' :
of Increase
Man-Made Sources
Fossil Fuel Combustion,
Deforestation
Landfills, Cattle Raising,
Rice Growing,
Natural Gas Handling
Agricultural Soil Management,
Fuel Combustion
Refrigerants,
Foam-Blowing Agents,
Semiconductor Production
Action of sunlight upon air
polluted by motor vehicle
exhaust and power plants.
How Is the Climate Changing?
The 1980s and 1990s were the warmest decades of
the 20th century, and the 1990s were likely1 to
have been the warmest decade in at least the
last thousand years in the Northern
Hemisphere. However, the varying methods
used for measuring temperature in the past
millennium must be considered in evaluat-
ing such trends.
As temperatures climbed during the past
century (marked by an intermittent cool
period from 1940-1970), average precipitation
also increased in many areas. For example, in
portions of the United States, 24-hour heavy rains
now occur with greater frequency.
What Do Climate Science Experts Say?
The Intergovernmental Panel on Climate Change (IPCC), an international
body of climate scientists and government officials, recently concluded
that there is "new and stronger evidence that most of the warming observed
over the last SO years is attributable to human activities."2 A June 2001
report from the National Academy of Sciences (NAS) re-confirmed that this
conclusion accurately portrays the thinking of the scientific community.3
However, the NAS also warned that "[b]ecause there is considerable uncer-
tainty in current understanding of how the climate system varies normally
and reacts to emissions of greenhouse gases and aerosols, current estimate
of the magnitude of future wanning should be regarded as tentative and
subject to future adjustments (either upward or downward)."
The IPCC, using a wide range of emissions scenarios and assumptions,
projects that globally averaged temperatures could rise between 2.5-10.4
degrees Fahrenheit (1.4-5.8 degrees Celsius) by 2100. However, the most
likely temperature estimates are thought to be in the range of 3.3-8.8
degrees F (1.7-4.9 degrees C), according to one study.4
The NAS cautioned that global warming "could well have serious adverse
societal and ecological impacts by the end of this century" if the tempera-
ture increases approach the high-end projections of the IPCC. The NAS
also stated: "Climate projections will always be far from perfect.
Confidence limits and probabilistic information, with their basis, should
always be considered as an integral part of the information that climate
scientists provide to policy- and decision-makers. Without them, the IPCC
could give an impression that the science of global warming is 'settled,'
even though uncertainties still remain."
TEMPERATURE VARIABILITY IN THE NORTHERN HEMISPHERE SINCE 1000 A.D.
BASE PERIOD: 1902-1980
DATA FROM THERMOMETERS (YELLOW)
ANDFROMTREER1NCLS, CORALS, ICE CORES, AND HISTORICAL RECORDS (BLUE)
1400
1800
YEAR
SOURCE: MICHAEL E. MANN, UNIVERSITYOF VIRGINIA. DATA AND MORE
INFORMATION AVAILABLE AT HTnV/W\yW.PEOPLE.VIRGINIA.EOU/-MEM6U/MBH95.K™L
Other signs around the world that the Earth is warming:
Arctic sea ice is thinning and
decreasing in extent.
Tropical and temperate
mountain glaciers are melting.
Winter snow cover in the
Northern Hemisphere is
decreasing.
Sea level is rising.
Although it is inappropriate to
attribute any single rainstorm or
heat wave to global warming, the
balance of evidence suggests-that a
general.global warming is currently
underway, the causes of which
appear to be both natural and
human-induced.
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25,000
20,000
Global Emissions and Atmospheric
Concentration of COz
1750'1997
ATMOSPHERIC CONCENTRATIONS
MEASURED DIRECTLY
P
u
15,000
o
l'
10,000
5,000
ATMOSPHERIC CONCEffTRATlONS
0 I
1750 1775 1800 1825 1850 1875 1900 1925 1950 1975
'SOURC&CARBON DIOXIDEINFORMATIONANALYSISCEKrERiHOI.
375
350
325
300
275
What Might We Expect in the Future?
Current scientific guidance suggests that climate changes may affect our
world in the following ways:
Climate change will likely produce positive and negative effects for small
temperature increases. For large temperature increases, the effects of
climate change may* become increasingly negative as it becomes more
difficult for ecosystems, communities,, and species to adapt.
In' the short term, increased carbon dioxide in the atmosphere and
warmer temperatures will likely enhance the growth of certain plants,
benefiting agriculture and speeding tree growth as well. In the long term,
changes in climate may require farmers to adapt by changing the kinds
of crops they grow. Adaptation will very likely be more difficult if the
climate changes abruptly and unpredictably.
Because warmer air accelerates evaporation, the potential for heavy rains
and floods will very likely increase due to increased water vapor in the
atmosphere. At the same time, some areas will likely experience more
droughts due to decreased soil moisture and sporadic rainfall.
Changes in overall storm activity during the 20th century have been
difficult to assess due to a lack of adequate data. Discernible changes in
the frequency of hurricanes, tornadoes, thunder days, or hail events have
not emerged. Accordingly, it is difficult to draw definitive conclusions
about future storm activity. However,.peak hurricane wind speeds are
likely to increase over some areas.
Diseases and insects that now exist primarily in warmer climates may spread
into other parts of the world, challenging the ability of public health pro-
grams to contain them. Cold-related health stresses will likely decline,
while heat stresses and smog-induced respiratory illnesses will likely increase.
Warming air melts land ice, and warming water expands, both causing
sea level to rise. The IPCC projects sea levels will rise between 4 and 35
inches (.09 to .88 meters) globally by 2100. In the United States, likely sea
level rise effects include enhanced coastal erosion, coastal flooding, loss
of coastal wetlands, and increased risk from storm surges.
Outdoor enthusiasts may experience changes in fishing and hunting
opportunities. Populations of cold-water fish such as brook trout could
be depleted in some parts of the country, while there may be an increase
in the number of warm-water fish such as catfish and largemouth bass.
Warmer temperatures and increased precipitation will likely affect the
habitats and migratory patterns of many types of wildlife. Recent studies
have shown that climate change may already be affecting frog, penguin,
polar bear, and butterfly populations, stressing coral, and leading to
shifts in forest ranges and early blooms of some plant species.
What Are Some of the Scientific Uncertainties?
Important scientific questions remain about how much warming will occur,
how fast it will pccur, and the degree to which humans and ecosystems will
be affected by its potential effects. Further progress in resolving these issues
poses a number of scientific challenges:
Since both humans and nature affect climate, determining the relative
contribution to the observed warming from human activities and natural
causes remains a challenge.
Scientists use computer-based climate models to help reproduce past
climates and to create scenarios of future climate change. These models do
a reasonably good job of simulating the large-scale aspects of the present
climate system. Despite these considerable successes, models contain
weaknesses that result in important uncertainties in model forecasts.
Scientists generally have more confidence in model projections of global-
scale changes in surface temperatures, precipitation, and sea level, and
significantly less confidence in regional scale projections. .
1 In all instances within the text, "very likely" indicates a 90-99 percent chance of occurrence, and "likely" indicates
a 66-90 percent chance as defined by the Intergovernmental Panel on Climate Change (IPCC).
1 Intergovernmental Panel on Climate Change. 2001. Summary for Policymakers, IPCC WCI Third Assessment
Report. Geneva.
! National Research Council. 2001. Climate Change Science: An Analysis of Some Key Questions.
National Academy Press, Washington, D.C.
' Wigley, T.M.L. and S.C.B. Raper. 2001. Interpretation of high projections of global-mean warming.
Science 293:451-454.
* "May/could" indicates medium confidence of occurrence, or a 33-67 percent probability as defined by the IPCC.
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