Climate Change: An Overview of the Science

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Climate ChangeAn Overview of the Science

• Anthony J. Broccoli
• Director, Center for Environmental
  PredictionDepartment of Environmental Sciences
• Rutgers University
• Conference on Carbon Politics and FinanceFordham
  UniversityNew 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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Greenhouse gases are now higher than any time in
the past 650,000 years.
Source Brook, E., 2005 Tiny bubbles tell all,
Science, 310, 1285-1287.
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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
  earths cooling mechanism that balances the
  heating from the suns 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
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sTe4
sTe4
effective radiating level
temperatureincreases
effective radiating level
more greenhouse gases?infrared opacity
increases?effective radiating level rises
288 K
255 K
288 K
255 K
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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 temperature was 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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Projections of Future Climate
Variations among colored lines represents
uncertainty due to uncertainty in future
emissions.
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Simulating Future Climate Change
Source NOAA Geophysical Fluid Dynamics Laboratory
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Potential Climate Change Impacts
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Future Emissions Scenarios
Some scenarios showdecreased emissionsin latter
half of 21stcentury
Even with substantialreductions in
emissions,CO2 would rise to 2xpreindustrial
levels
All scenarios showincreasing emissionsduring
next severaldecades
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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
Future emissions
Additional zero-emission warming (aka
commitment)
Warming to date
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Outstanding scientific questions

• How sensitive is the earths 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, noreasters)?
• Are there tipping points in the climate system?
• What impacts will climate change have on natural
  systems and society?