climate change: an overview of the science anthony j. broccoli director, center for environmental...
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Climate Change:An Overview of the Science
Anthony J. BroccoliDirector, Center for Environmental Prediction
Department of Environmental SciencesRutgers University
Conference on Carbon Politics and FinanceFordham University
New York, NYOctober 29, 2010
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Why do we care about carbon emissions?
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[Source: Intergovernmental Panel on Climate Change, Third Assessment Report]
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Preindustrial
Today
[Source: Brook, E., 2005: Tiny bubbles tell all, Science, 310, 1285-1287.]
Greenhouse gases are now higher
than any time in the past 650,000
years.
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Three lines of evidence link CO2 and climate:
• Basic physics
• Observations
• Modeling
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Three lines of evidence link CO2 and climate:
• Basic physics
• Observations
• Modeling
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Basic physics of CO2 and climate
• If an object receives energy in the form of visible light, as the earth does from the sun, it warms up.
• The warmer an object is, the more energy it emits in the form of infrared light.
• CO2 and water vapor are “greenhouse gases” that absorb infrared light, making it more difficult for energy to escape into space. This is the earth’s cooling mechanism that balances the heating from the sun’s visible light.
• Without greenhouse gases the earth would be much colder (i.e., its average temperature would be well below freezing).
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The “atmospheric window”
Infrared light can escapethrough atmospheric window
CO2 partially blocksatmospheric window
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Te4
Temperature
288 K255 K
Temperature
288 K255 K
temperatureincreases
Te4
more greenhouse gases↓
infrared opacity increases↓
effective radiating level rises
effective radiating level
effective radiating level
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Three lines of evidence link CO2 and climate:
• Basic physics
• Observations
• Modeling
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Source: NASA/Goddard Institute for Space Studies
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Northern Hemisphere Temperature Reconstructions
“It can be said with a high level of confidence that global mean surface temperaturewas higher during the last few decades of the 20th century than during any comparable period during the preceding four centuries”“…the committee finds it plausible that the Northern Hemisphere was warmer during the last few decades of the 20th century than during any comparable period over the preceding millennium.” National Research Council
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Source: Polar Research Group, Univ. of Illinois
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Three lines of evidence link CO2 and climate:
• Basic physics
• Observations
• Modeling
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What Are Climate Models?
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Coupled Climate Model Schematic
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Blue: Natural Pink: Natural + Human-induced
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Variations among colored lines represents uncertainty due to uncertainty in future emissions.
Projections of Future Climate
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Source: NOAA Geophysical Fluid Dynamics Laboratory
Simulating Future Climate Change
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Potential Climate Change Impacts
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Future Emissions Scenarios
All scenarios showincreasing emissionsduring next severaldecades
Some scenarios showdecreased emissionsin latter half of 21st
century
Even with substantialreductions in emissions,CO2 would rise to 2xpreindustrial levels
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The Atmospheric CO2 Balance
Human-produced emissions of CO2
Uptake of CO2 by ocean, vegetation, and solid earth
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More Warming in the Pipeline
Warming to date
Additional “zero-emission” warming (aka “commitment”)
Future emissions
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Outstanding scientific questions
• How sensitive is the earth’s climate? In other words, how much will the climate change for a given change in greenhouse gas concentrations?
• How rapidly will sea level rise? Will Greenland and Antarctica melt more quickly or more slowly?
• How will climate change affect precipitation patterns?• How will climate change affect severe storms (e.g.,
tornadoes, hurricanes, nor’easters)?• Are there “tipping points” in the climate system?• What impacts will climate change have on natural
systems and society?