Global Climate Change: Past and Future

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• Global Climate Change Past and Future

Michael E. Mann Departments of Meteorology and
Geosciences and Earth and Environmental Systems
Institute Director, Earth System Science
Center, Penn State University
Straub Environmental Lecture Salem, Oregon May
31, 2007
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The balance of evidence suggests that there is a
discernible human influence on global climate '
Intergovernmental Panel on Climate Change (United
Nations), Second Assessment Report, 1996
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There is new and stronger evidence that most of
the warming observed overthe last 50 years is
attributable to human activity'
Intergovernmental Panel on Climate Change (United
Nations), Third Assessment Report, 2001
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Most of the observed increase in globally
averaged temperatures since the mid-20th century
is verylikely due to the observed increase in
anthropogenic greenhouse gas concentrations
Intergovernmental Panel on Climate Change (United
Nations), Fourth Assessment Report, 2007
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OBSERVATIONS
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Surface Temperature Changes
Gray back to beginning of 20th century
Boxes back to mid 19th century
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Surface Temperature Changes
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Surface Temperature Changes
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Internally Consistent Changes in Other Variables
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Greenhouse Gases and Warming
CO2
Related?
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ENHANCED GREENHOUSE EFFECT?
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TREE RINGS
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CORALS
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ICE CORES
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VARVED LAKE SEDIMENTS
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HISTORICAL DOCUMENTS
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RECONSTRUCTED GLOBAL TEMPERATURE PATTERNS
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(No Transcript)
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From Wikipedia
Reconstructions of Northern Hemisphere mean
temperatures for the last 1000 years and
instrumental record (black line)
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Mt Kilimanjaro
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Mt Kilimanjaro
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Thompson, L. G., Mosley-Thompson, E., Davis, M.
E., Lin, P. N., Henderson, K., and Mashiotta, T.
A., 2003, Tropical glacier and ice core evidence
of climate change on annual to millennial time
scales, Climatic Change, v. 59, p. 137-155.
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MODEL SIMULATIONS
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The climate represents a coupled system
consisting of an atmosphere, hydrosphere,
biosphere, and cryosphere
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General Circulation Models (GCMs) take into
account the full three-dimensional structure of
the atmosphere and ocean
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CLIMATE FORCINGS
Volcanism
Solar
Natural
Crowley, T.J., Causes of Climate Change Over the
Past 1000 Years, Science, 289 270-277, 2000.
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CLIMATE FORCINGS
Anthropogenic
Industrial Aerosols
Greenhouse Gases
Climate Change 2001 The Scientific Basis,
Houghton, J.T., et al. (eds.), Cambridge Univ.
Press, Cambridge, 2001
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Simulated Annual Global Mean Surface Temperatures
Climate Change 2001 The Scientific Basis,
Houghton, J.T., et al. (eds.), Cambridge Univ.
Press, Cambridge, 2001
Forced Model simulations
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Simulated Annual Global Mean Surface Temperatures
Climate Change 2001 The Scientific Basis,
Houghton, J.T., et al. (eds.), Cambridge Univ.
Press, Cambridge, 2001
Forced Model simulations
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Simulated Annual Global Mean Surface Temperatures
Climate Change 2001 The Scientific Basis,
Houghton, J.T., et al. (eds.), Cambridge Univ.
Press, Cambridge, 2001
Forced Model simulations
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Jones, P.D., Mann, M.E., Climate Over Past
Millennia, Reviews of Geophysics, 42, RG2002,
doi10.1029/2003RG000143, 2004.
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Future Surface Temperatures Trends?
Climate Change 2001 The Scientific Basis,
Houghton, J.T., et al. (eds.), Cambridge Univ.
Press, Cambridge, 2001
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Model Predictions
Climate Change 2001 The Scientific Basis,
Houghton, J.T., et al. (eds.), Cambridge Univ.
Press, Cambridge, 2001
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Model Predictions
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Possible Impacts?
Warmer summer temperatures less/no increase in
continental precipitation
more frequent summer drought
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Possible Impacts?
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Possible Impacts?
Sea Level Rise
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Possible Impacts?
10 meters
Sea Level Rise
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Possible Impacts?
Katrina (Aug 05)
More Destructive Hurricanes
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Possible Impacts?
Rita (Sep 05)
More Destructive Hurricanes
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Possible Impacts?
Wilma (Oct 05)
More Destructive Hurricanes
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Climate Model Predictions
Knutson, T. K., and R. E. Tuleya, 2004 Impact of
CO2-induced warming on simulated hurricane
intensity and precipitation Sensitivity to the
choice of climate model and convective
parameterization. Journal of Climate, 17(18),
3477-3495.
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Hurricane Statistics
Emanuel, K. (2005), Increasing destructiveness of
tropical cyclones over the past 30 years, Nature,
online publication published online 31 July 2005
doi 10.1038/nature03906
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CONCLUSIONS

• Recent global surface temperatures are
  unprecedented in a long-term context

• It is difficult to explain the recent surface
  warming in terms of natural climate variability

• Recent surface warming is largely consistent with
  simulations of the effects of anthropogenic
  influence on climate

• Possible impacts of anthropogenic climate change
  this century include increased drought, coastal
  flooding, and more destructive Atlantic Hurricanes

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RealClimate is a commentary site on climate
science by working climate scientists for the
interested public and journalists. We aim to
provide a quick response to developing stories
and provide the context sometimes missing in
mainstream commentary.
Gavin Schmidt, Michael Mann
Eric Steig, William Connolley, Ray Bradley,
Stefan Rahmstorf, Rasmus Benestad, Caspar Ammann,
Thibault de Garidel, David Archer, Ray
Pierrehumbert