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Twenty-four Frequently Asked Questions on Climate Change
This short guide contains answers to twenty-four commonly asked questions about
climate change. It is divided into three sections. The first fifteen questions address
climate change science; the next seven, the potential impacts of a changed climate;
and the last two, what scientific research is needed and how it should be organized.
Climate Change Science
1. How does the climate system work?
The sun provides the energy that drives the climate system. The intensity of solar
energy reaching the earth and its interaction with the atmosphere and the earth’s
surface are the key factors determining climate. The greenhouse effect, which
traps thermal energy re-radiated by the earth in the atmosphere, is one of the
important interactions.
2. What are greenhouse gases?
Greenhouse gases are gases (water vapor, carbon dioxide, methane, nitrous oxide,
and others) that can absorb the thermal energy emitted by the earth, creating the
greenhouse effect, which warms the earth.
3. How has the concentration of greenhouse gases in the atmosphere
changed since 1750?
Atmospheric concentrations of carbon dioxide, methane and the other greenhouse
gases have increased since 1750.
4. What other changes have affected the climate system since 1750?
Since 1750, there have been increases in the amount of particulates in the
atmosphere, changes in land cover, and the creation of contrails in the upper
atmosphere, all of which can affect the climate system.
The George C. Marshall Institute
1625 K Street, NW – Suite 1050
Washington, D.C. 20006
202-296-9655 – fax 202-296-9714
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5. How accurate are measurements of the earth’s temperature?
Surface temperature records contain biases that could introduce errors 0.2-0.3° C
(0.4-0.6o F), or one-third to one-half of the warming observed during the 20th
century.
6. How accurate are satellite measurements of the temperature of the
troposphere?
Satellite measurements of the temperature of the troposphere, once corrected for
known sources of error, appear to be very accurate.
7. Are there differences between measurements of surface
tropospheric temperatures and if so, are the differences real?
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Satellite temperature measurements show the troposphere warming at a slower
rate than the surface. In 2000, the National Research Council concluded that the
differences were real and could not be explained with our current scientific
understanding.
8. What is the greenhouse “fingerprint”? Has it been found?
The greenhouse “fingerprint” refers to predictions from current theory and climate
model simulations that tropospheric temperatures should rise faster than surface
temperatures. A comparison of satellite and surface temperature data shows just
the opposite.
9. Has the earth’s temperature increased over the last 100 years in
step with increasing atmospheric concentrations of greenhouse
gases?
No. Greenhouse gas concentrations have increased steadily, but global average
surface temperature declined from 1940 to 1975.
10.
What influence does the sun have on global climate?
The sun provides the energy that drives the climate system. Long-term variations
in the intensity of solar energy reaching the earth are believed to cause climate
change on geological time-scales. New studies indicate that changes in the sun’s
magnetic field may be responsible for shorter-term changes in climate, including
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much of the climate of the 20 century.
The George C. Marshall Institute
1625 K Street, NW – Suite 1050
Washington, D.C. 20006
202-296-9655 – fax 202-296-9714
www.marshall.org email: [email protected]
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11.
How much does the global climate vary naturally?
Climate scientists do not know the answer to this question, but the available data
suggest that natural climate can change very rapidly.
12.
Are computer simulations of the earth’s climate accurate?
No. Because knowledge of the detailed working of the climate system is
incomplete, climate models can provide only poor simulations of the earth’s
climate. For example, estimates of the temperature rise that would result from a
doubling of atmospheric concentration of carbon dioxide vary by a factor of three.
13. Isn’t the temperature rise since 1975 proof that humans are
changing the climate?
No. The claim that the temperature rise since 1975 is the result of human
emissions of greenhouse gases is based on climate model studies that suffer all of
the shortcomings and limitations discussed in Question 12, and historical data on
greenhouse gas and particulate emissions that can only be guessed at.
14.
Can we predict future climate?
Not now, and possibly not ever. Current climate models have not been validated,
and even if climate models can be validated, the inputs required to determine future
human emissions of greenhouse gases and aerosols are probably unknowable.
15. How will we know if climate has changed and whether the change
was caused by human activities?
Climate change is defined as a change in climate that is greater than natural
climate variability. Natural climate variability is currently unknown, but should be
knowable with further research. Validated climate models can be used to
determine the cause of the change. If the change is large enough, it may be
possible to determine its cause without using a model.
Climate Change Impacts
16. How much will the earth’s temperature rise if the amount of
human-made greenhouse gas in the atmosphere continues to rise for
the next 100 years?
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1625 K Street, NW – Suite 1050
Washington, D.C. 20006
202-296-9655 – fax 202-296-9714
www.marshall.org email: [email protected]
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Climate scientists do not know the answer to this question for two reasons. First,
because the rates of human emissions of greenhouse gases and particulates
decades from now are unknowable. Second, because our understanding of the
climate system is incomplete the impacts of human emissions on climate are highly
uncertain. These two sources of uncertainty are about equal in magnitude.
17.
Will the earth’s climate change in other ways?
Increased precipitation and increases in flood and droughts are a common
prediction about future climate. However, climate model projections, even if one is
willing to accept them, do not show consistent changes in precipitation. Floods
and droughts are affected by so many other factors that determining the affect of
climate change is very difficult.
18. Will climate change produce a major rise in sea level and cause
flooding?
Not for the next century. Projections for longer time-scales are too uncertain to be
credible.
19.
Will climate change produce more violent storms?
Unlikely, since the warming of the 20th century did not produce any significant
change in storm frequency or intensity. Future trends cannot be accurately
predicted because climate models do an even poorer job of simulating small events
like hurricanes than they do in simulating global average climate.
20.
Will climate change cause the spread of infectious diseases?
No. Climate is a relatively small factor in determining the rate of vector-borne
infectious disease. Appropriate public health measures are the key to controlling
both the current incidence of these diseases and any increase due to climate
change.
21.
Will climate change lead to massive species extinctions?
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No. The warming of the 20 century was implicated in the extinction of only one
species, indicating that species are more resilient to climate change than indicated
in modeling studies.
The George C. Marshall Institute
1625 K Street, NW – Suite 1050
Washington, D.C. 20006
202-296-9655 – fax 202-296-9714
www.marshall.org email: [email protected]
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22. Could human emissions of greenhouse gases cause the next ice
age?
No. Human emissions of greenhouse gases causing an ice age do not agree with
our scientific understanding of either ice ages or the climate system. Ice ages are
believed to be caused by changes in the earth’s orbit and tilt that cause reductions
in the amount of solar energy reaching the earth’s surface.
Climate Science Research
23. What are the most important priorities for the U.S. Climate
Change Science Program (CCSP)?
The most important priorities for the CCSP are:
(1) Achieving the theoretical understanding of important climate processes,
including the roles of water vapor, clouds, particulates, and ocean currents,
needed to understand better potential human influences on the climate system.
(2) Building and maintaining an effective climate observation network.
(3) Developing empirical knowledge and theoretical understanding of adaptation.
24. Aren’t most scientists in agreement on climate change?
should we listen to those who disagree with the consensus?
Why
Scientific knowledge doesn’t move forward because there is a consensus. It moves
forward because of new ideas that depart from the consensus.
The George C. Marshall Institute
1625 K Street, NW – Suite 1050
Washington, D.C. 20006
202-296-9655 – fax 202-296-9714
www.marshall.org email: [email protected]