9/29/2010
Greenhouse effect
and global warming
The Greenhouse Effect and
Atmospheric Warming
• Why is it called greenhouse effect?
• What is the difference between the
greenhouse effect and real greenhouses?
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The Greenhouse Effect and
Atmospheric Warming
• Greenhouse gases make up about 1% of the
earth atmosphere
• Without the greenhouse gases, the earth’s
average temperature would be close to -18°C
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Most important greenhouse gases
Gas
Water Vapor
Carbon Dioxide
Methane
Ozone
Formula
H2O
CO2
CH4
O3
Contribution (%)
36 – 72 %
9 – 26 %
4–9%
3–7%
Do these numbers imply that CO2 is
responsible for 9-26% of the earth warming?
Greenhouse gases
• Water vapor is the most dominant greenhouse gas.
• Water vapor is the dominant positive feedback in the
climate system and amplifies warming caused by
changes in atmospheric CO2.
• This positive feedback is why climate is so sensitive
to CO2 warming.
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Main non-gas contributors to the
greenhouse effect: Clouds
• Actually clouds do both
– 1)act as insulation warming the earth
– 2)reflect insolation cooling the earth
How does the altitude of the clouds
influence the greenhouse effect?
Clouds and Greenhouse effect
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CO2 and warming
• Why does CO2 receive so much attention in
the climate warming context?
CO2 and warming
• Carbon dioxide accounts for a significant
fraction of the enhanced greenhouse effect.
• The level of carbon dioxide in the atmosphere
is increasing by more than 10% every 20 yrs
due to human activity.
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CO2 and warming
• Natural sources of atmospheric CO2
– volcanic outgassing
– combustion of organic matter
– respiration of aerobic organisms
CO2 and warming
Anthropogenic sources?
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Source epa.gov
Source epa.gov
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CO2 and warming
• Natural land and ocean CO2 sinks removed
57% of all CO2 emitted from human activities
during the 1958-2008
• Atmospheric lifetime of CO2 is 50 to 200 yrs.
• Global warming will continue to affect the
Earth for hundreds of years.
What about CH4 and warming?
• Methane is 25 times more potent as a
greenhouse gas than CO2 (but it’s at lower
concentrations in the atmosphere)
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What about CH4 and warming?
• Largest anthropogenic sources of methane
emissions (for USA only):
– decomposition of wastes in landfills
– ruminant digestion
– manure management associated with livestock
– natural gas and oil systems
What about CH4 and warming?
• There is some uncertainty about the
potential future contributions of CH4 to
global warming.
• Positive feedbacks triggered by elevated
temperatures could release large amounts
of CH4 to the atmosphere.
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• Let’s now see some of the data…
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