Frequently Asked Questions
ABOUT GLOBAL WARMING
AND CLIMATE CHANGE:
Back to Basics
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The Earth's climate is changing. In
most places, average temperatures
are rising. Scientists have observed
a warming trend beginning
around the late 1800s.
The most rapid
warming has occurred
in recent decades. Most
of this recent warming
is very likely the result of
human activities.
Many human activities release "greenhouse gases"
into the atmosphere. The levels of these gases
are increasing at a faster rate than at any time in
hundreds of thousands of years.
We know that greenhouse gases trap heat. If
human activities continue to release greenhouse
gases at or above the current
rate, we will continue to increase
average temperatures around
the globe. Increases in global
temperatures will most likely
change our planet's climate in
ways that will have significant
long-term effects on people and
the environment.
This fact sheet addresses the
most frequently asked questions
about the science of global
warming and climate change.
The Intergovernmental Panel on
Climate Change's (IPCC) Fourth
Assessment Report (2007)
serves as the key reference for this brochure. The
IPCC was formed jointly in 1 988 by the United
Nations Environment Programme and the United
Nations World Meteorological Organization. The
IPCC brings together the world's top scientists,
economists and other experts, synthesizes
peer-reviewed scientific literature on
climate change studies, and produces
authoritative assessments of the current
state of knowledge of climate change.
The Greenhouse Effect
Q. What is the
greenhouse effect?
A. The Earth's greenhouse effect is a natural
occurrence that helps regulate the temperature of
our planet. When the Sun heats the Earth, some of
this heat escapes back to space. The rest of the heat,
also known as infrared radiation, is trapped in the
atmosphere by clouds and greenhouse gases, such
as water vapor and carbon dioxide. If all of these
greenhouse gases were to suddenly disappear, our
planet would be 60°F colder and would not support
life as we know it.
Human activities have enhanced the natural
greenhouse effect by adding greenhouse gases
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According to the National Academy of Sciences;
however, "the phrase 'climate change' is growing
in preferred use to 'global warming' because it
helps convey that there are [other] changes in
addition to rising temperatures."
Climate change refers to any distinct change
in measures of climate lasting for a long period of
time. In other words, "climate change" means major
changes in temperature, rainfall, snow, or wind
patterns lasting for decades or longer. Climate change
may result from:
• natural factors, such as changes in the Sun's energy
or slow changes in the Earth's orbit around the Sun;
• natural processes within the climate system (e.g.,
changes in ocean circulation);
• human activities that change the atmosphere's
make-up (e.g, burning fossil fuels) and the land
surface (e.g., cutting down forests, planting trees,
building developments in cities and suburbs, etc.).
Global warming is an average increase in
temperatures near the Earth's surface and in
the lowest layer of the atmosphere. Increases in
temperatures in our Earth's atmosphere can contribute
to changes in global climate patterns. Global warming
can be considered part of climate change along with
changes in precipitation, sea level, etc.
Global change is a broad term that refers to changes
in the global environment, including climate change,
ozone depletion, and land use change.
Carbon Dioxide and Methane Concentrations Over the Last 10,000 Years
to the atmosphere, very likely causing the Earth's
average temperature to rise. These additional
greenhouse gases come from burning fossil fuels
such as coal, natural gas, and oil to power our
cars, factories, power plants, homes, offices, and
schools. Cutting down trees, generating waste
and farming also produce greenhouse gases.
Q. What are the most important
greenhouse gases? Where are they
coming from and how have they
changed?
A. Many greenhouse gases, like water vapor and
carbon dioxide (CO2), occur naturally. Fuel burning
and other human activities are adding large amounts
of carbon dioxide and other gases to the natural mix
at a faster rate than at any other time on record. Other
important greenhouse gases produced by human
activity include methane (CH4), nitrous oxide (N2O),
hydrofluorocarbons (MFCs), perfluorocarbons (PFCs)
and sulfur hexafluoride (SF6).
Since 1 750, atmospheric concentrations of
CO2, CH4 and N2O have increased by over
36 percent, 148 percent and 18 percent,
respectively. Scientists have concluded that
this is due primarily to human activity.
Climate Change,
Global Warming, and
Global Change Defined
Q. How are the
terms climate
change, global
warming, and
global change
different?
A, The term climate
change is often used
as if it means the
same thing as the
term global warming.
350
X
o
300
250
1
2000
— 1500
1000
500
10,000 years ago
Present
1 0,000 years ago
Present
Atmospheric concentrations of carbon dioxide (in parts per million) and methane (in parts per billion) over the last ] 0,000 years
(large panels) and since 1750 (inset panels). Measurements are shown from ice cores (symbols with different colors for different
studies) and atmospheric samples (red lines). Source: IPCC, 2007
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Present and Future
Climate Change
Q. Is our planet warming?
Annual Global Temperature
Over Oceans and Land
Year
Annual global surface temperature departure (also known as anomalies) from
1901-2000 average for the period 1880-2007. Source: NOAA, 2007
A. Yes. The global temperature record shows an average
warming of about 1.3°F over the past century (see graph).
According to the National Oceanic and Atmospheric
Administration (NOAA), seven of the eight warmest years
on record have occurred since 2001. Within the past 30
years, the rate of warming across the globe has been
approximately three times greater than the rate over the
last 100 years. Past climate information suggests the
warmth of the last half century is unusual in at least the
previous 1,300 years in the Northern Hemisphere.
The IPCC concluded that warming of the Earth's
climate system is now "unequivocal" (i.e., "definite").
The IPCC bases this conclusion on observations of
increases in average air and ocean temperatures,
melting of snow and ice, and average sea level
across the globe.
Late Summer Arctic Sea Ice Changes
Ice is melting. Arctic sea ice, an indicator of climate change, set a record
low in September 2007. Sea ice extent was 38 percent below the 1979-2007
average. Source: NASA 2007
Q. Are human activities responsible
for the warming?
A. IPCC scientists believe that there is a greater than
90 percent chance that most of the warming we have
experienced since the 1 950s is due to the increase in
greenhouse gas emissions from human activities.
Q. How do scientists project future
climate change?
A, The Earth's climate is very complex and involves
the influences of air, land, and oceans on one
another. Scientists use computer models to study
these interactions. The models project future
climate changes based on expected changes to the
atmosphere. Though the models are not exact, they
are able to simulate many aspects of the climate.
Scientists reason that if the models can mimic currently
observed features of the climate, then they are also
most likely able to project future changes.
Q. How much will the Earth warm
if emissions of greenhouse gases
continue to rise?
Warming Projections to 2100
4
3-
2-
variability between models-
high growth (A2)-
moderate growth (A1B)-
observed
warming
0
1900
2000
Year
2100
Temperature pro/ecfions to the year 2 ] 00, based on a range of emission scenarios and
global climate models. Scenarios that assume the highest growth in greenhouse gas
emissions provide the estimates in the top end of the temperature range. The orange
line ("constant CO2") projects global temperatures with greenhouse gas concentrations
stabilized at year 2000 levels. Source: NASA (adapted from IPCC, 2007)
A. If humans continue to emit greenhouse gases at
or above the current pace, we will probably see an
average global temperature increase of 3 to 7°F by
2100, and greater warm ing after that. Temperatures
in some parts of the globe (e.g., over land and in the
polar regions) are expected to rise even more.
Even if we were to drastically reduce greenhouse gas
emissions, returning them to year 2000 levels and
holding them constant, the Earth would still warm
about 1 °F over the next 100 years. This is due to the
long life time of many greenhouse gases and the slow
cycling of heat from the ocean to the atmosphere.
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Q. How will a warming climate affect
precipitation?
A. Rising temperatures will intensify the Earth's water
cycle. Increased evaporation will make more water
available in the air for storms, but contribute to drying
over some land areas. As a result, storm-affected
areas are likely to experience increases in precipitation
and increased risk of flooding. But areas located far
away from storm tracks are likely to experience less
precipitation and increased risk of drought. In the
U.S., warming is expected to cause a northward shift
in storm tracks, resulting in decreases in precipitation
in areas such as the Southwest U.S. but increases in
many areas to the north and east. However, these
changes will vary by season and depend on weather
fluctuations.
Precipitation Projection for
North America 2100
90°N
70°N
50°N
30°N
Increase in Likelihood of
Extremes in a Warmer Climate
10°N
180°W
140°W
100°W
20°W
Precipitation changes averaged over 21 climate models between 1980 to 1999
and 2080 to 2099. As storm tracks shift north, precipitation tends to increase in
the middle and northern latitudes but decrease in the southern latitudes in North
America. Yellow shades indicate decreases in precipitation and green shades
indicate increases in precipitation. Darker shades indicate larger increases or
decreases. Source: (PCC, 2007
Q. Will a warming climate make
temperatures more extreme?
A. Most scientists think that a warming climate
will alter the frequency and severity of extreme
temperature events. In general, they expect increases
in heat waves and decreases in cold spells. These
effects will vary from place to place.
More
Record Hot
Weathe*
Cold
Average
Hot
Global warming increases the likelihood it will be hot or very hot and decreases,
but does not eliminate, the likelihood it will be cold or very cold.
Source: IPCC, 2007
Q. How will a warming climate affect
hurricanes?
A. Because warm sea surface temperatures energize
hurricanes, a warming climate is likely to make
hurricanes more intense. Hurricanes in the future will
probably have stronger peak winds and increased
rainfall. The relationship between sea surface
temperatures and the frequency of hurricanes is less
clear. There is currently no scientific consensus on how
a warming climate is likely to affect the frequency of
hurricanes, but research continues.
Q. How will a warming climate and
climate change affect the polar ice
sheets, sea levels, and sea ice?
A. Polar ice sheets (such as those on Greenland and
Antarctica) are some of the largest surface features on our
planet. Any changes to them, however small, could have far-
reaching effects. Polar ice sheets potentially will accumulate
more snow and ice because of an increase in precipitation.
However, overall melting due to global warming is expected
to reduce the size and extent of the polar ice sheets.
Melting of polar ice and land-based glaciers is expected to
contribute to sea eve rise. The IPCC projects a six inch to
two foot rise in sea level during the 21 st century.
Sea level rise may be greater if there are sudden
increases in ice sheet melt. Such increases have already
been observed but their effects have not yet been
incorporated into current projections of sea level rise.
The stability of the West Antarctic Ice Sheet is of
particular concern. A sudden collapse of the ice sheet
could raise sea levels 16 to 20 feet. The IPCC is unable
to estimate the likelihood or timing of such a collapse,
however, due to incomplete understanding of all the
processes affecting this ice sheet.
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Sea Level Changes and Projections
•200
1800
2MO
210C
Past and projected global average sea level. The gray shaded area shows the
estimates of sea level change from 1800 to 1870 when measurements were not
available. The red line is a reconstruction of sea level change measured by tide
gauges with the surrounding shaded area depicting the uncertainty The green line
shows sea level change as measured by satellite. The purple shaded area represents
the range of model pro/ecfions for a medium growth emissions scenario f/PCC SRES
AIBJ. For reference 100mm is about 4 inches. Source: IPCC, 2007
In addition to the ice sheets, sea ice is also melting.
Though the melting of floating sea ice that covers part
of the Arctic Ocean does not effect sea level, sea ice
is important for wildlife and for keeping the region
cool by reflecting sunlight back to space. If the Arctic
loses the reflective surface of ice and then the dark
Arctic Ocean absorbs more heat, the northern regions
may warm even more rapidly.
Q. How serious is a warming
of a few degrees?
A. The IPCC estimates it has warmed 1.2 to 1.4°F over
the past century and projects a further 3 to 7°F over the
21 st century. The increases may appear minor compared
to short-term weather changes from night to day and
winter to summer. In global climate terms, however,
warming at this rate would be much larger and faster
than any of the climate changes over at least the past
10,000 years.
Q. Will a warming climate have more
positive or negative effects?
A. A warming climate will have both positive and
negative impacts. Local impacts are the most difficult to
predict, making it a challenge to know exactly who or
what will be harmed or benefit.
Generally, the risk of negative impacts from climate
change increases the faster it warms. More rapid
climate change makes adapting to change more
difficult and costly. This is especially true for vulnerable
groups (such as the poor, the very young and older
adults) and fragile ecosystems which may struggle
to adapt to even small changes. The IPCC suggests
that temperature increases above the range of 3.5
to 5.5°F over the next 100 years would dramatically
increase the negative impacts of climate change. So
a major aim of climate action is to reduce the risk
and likelihood of large, rapid warming.
Health
Impacts
Heat-related deaths
Infectious diseases
Air quality-respiratory
illnesses
Climate Change Impacts
Temperature
Sea Level
Rise
Agriculture
Crop yields
Irrigration demand
Forest Impacts
Health, composition
and productivity
Water Resources
Changes in precipitation,
water qualify, ami water
supply
Wildlife _p
Loss of diversity
Species range shil.
oastal
Erosion and inundation
of coastal lands
Cost of protect!
vulnerable Ian
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Q. How might global warming and
climate change affect my health and
well-being?
A. Because global temperatures, precipitation, sea
levels and the frequency of some extreme weather are
expected to increase, climate change could affect you
in many ways. Our health, agriculture, forests, water
resources, energy, coasts, wildlife and recreational
opportunities would all react to climate changes.
Scientific results suggest that
climate changes may affect you
in the following ways:
Health: Longer, more intense and frequent heatwaves
may cause more heat-related death and illness. There
is virtual certainty of declining air quality in cities since
greater heat can also worsen air pollution such as
ozone, or smog. Insect-bourne illnesses are also likely to
increase as many insect ranges expand. Climate change
health effects are especially serious for the very young,
very old, or for those with heart and respiratory problems.
Conversely, warmer winter temperatures may reduce the
negative health impacts from cold weather.
Agriculture and Forestry: The supply and cost of
food may change as farmers and the food industry
adapt to new climate patterns. A small amount of
warming coupled with increasing CO2 may benefit
certain crops, plants and forests, although the
impacts of vegetation depend also on the availability
of water and nutrients. For warming of more than
a few degrees, the effects are expected to become
increasingly negative, especially for vegetation near
the warm end of its suitable range.
Water Resources: In a warming climate, extreme
events like floods and droughts are likely to become
more frequent. More frequent floods and droughts
will affect water quality and availability. For example,
increases in drought in some areas may increase
the frequency of water shortages and lead to more
restrictions on water usage. An overall increase in
precipitation may increase water availability in some
regions, but also create greater flood potential.
Coasts: If you live along the coast, your home may
be impacted by sea level rise and an increase in storm
intensity. Rising seas may contribute to enhanced
coastal erosion, coastal flooding, loss of coastal
wetlands, and increased risk of property loss from
storm surges.
Energy: Warmer temperatures may result in higher
energy bills for air conditioning in summer, and
lower bills for heating in winter. Energy usage is also
connected to water needs. Energy is needed for
irrigation, which will most likely increase due to climate
change. Also, energy is generated by hydropower in
some regions, which will also be impacted by changing
precipitation patterns.
Wildlife: Warmer temperatures and precipitation
changes will likely affect the habitats and migratory
patterns of many types of wildlife. The range and
distribution of many species will change, and
some species that cannot move or adapt may face
extinction.
Recreational opportunities: Some outdoor activities
may benefit from longer periods of warm weather.
However, many other outdoor activities could be
compromised by increased beach erosion, increased
heatwaves, decreased snowfall, retreating glaciers,
reduced biodiversity and changing wildlife habitats.
Resources
A great place to start is EPA's Climate Change Web
site at: www.epa.gov/climatechange
The site contains detailed information about
greenhouse gas emissions, science, effects of
climate change and what you can do.
Here are some other Web sites you may find useful:
Intergovernmental Panel on Climate Change
http://www.ipcc.ch
Climate Change Science Program
http://www.climatescience.gov
NASA's Global Warming Web site
http://earthobservatory.nasa.gov/Library/
GlobalWarmingUpdate
NASA's Climate Change—Eyes on the Earth Web site
http://climate.jpl.nasa.gov
NOAA's National Climatic Data Center
http://www.ncdc.noaa.gov
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SERA
United States
Environmental Protection
Agency
www.epa.gov/climatechange
Office of Air and Radiation (6207J)
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