climate change and global warming michael e. mann department of environmental sciences university of...
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Climate Change and Global Warming
Michael E. MannDepartment of Environmental Sciences
University of Virginia
Symposium on Energy for the 21st CenturyUniversity of Massachusetts
April 9, 2005
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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 over
the last 50 years is attributable to human activity'
Intergovernmental Panel on Climate Change (United Nations), Third Assessment Report, 2001
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THE EMPIRICAL RECORD
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Climatic Research Unit (‘CRU’), University of East Anglia
Surface Temperature Changes
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Shaded: 20th century
Boxes: since mid 19th century
Surface Temperature Changes
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Climate Change 2001: The Scientific Basis, Houghton, J.T., et al. (eds.),
Cambridge Univ. Press, Cambridge, 2001
Surface Temperature Changes
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1998 Global Temperature Pattern
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EL NINO/SOUTHERN OSCILLATION (“ENSO”)
Multivariate ENSO Index
(“MEI”)
Substantial interannual climate variability associated with ENSO, but decadal variability is also evident as well. The recent decadal trend towards El Nino conditions could be natural or anthropogenic.
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NORTH ATLANTIC OSCILLATION
Negative Phase Positive Phase
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This NAO trend could be Anthropogenic
NORTH ATLANTIC OSCILLATION
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“PACIFIC DECADAL OSCILLATION”
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There is evidence of multidecadal natural variability
in the North Atlantic ocean circulation
Atlantic Multidecadal Oscillation
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Greenhouse Gases and WarmingCO2
Related?
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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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Reconstructed Surface Temperatures
Climate Change 2001: The Scientific Basis, Houghton, J.T.,
et al. (eds.), Cambridge Univ. Press, Cambridge, 2001
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Moberg, A., Sonechkin, D.M., Holmgren, K., Datsenko, N.M., Karlen, W., Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data, Nature, 433, 613-617 (2005).
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Oerlemans, J., Extracting a climate signal from 169 Glacier Records, Science (express), March 3 (2005).
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CLIMATE MODELS
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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 take into
account the full three-dimensional structure of
the atmosphere and ocean
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This alone doesn’t guarantee that they should do a good job in describing climate change!
GCMs do a fairly good job of
describing the seasonal cycle in
surface temperature
January Temp (observations)
January Temp (model)
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Modeled Internal Natural Variability Observations
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INFLUENCE OF EXTERNAL FACTORS
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The climate is governed by external factors, including the intensity of solar output and volcanic aerosols
and greenhouse gas concentrations
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Solar Variations
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The climate is governed by external factors, including the intensity of solar output and volcanic aerosols
and greenhouse gas concentrations
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Volcanoes
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The climate is governed by external factors, including the intensity of solar output and volcanic aerosols
and greenhouse gas concentrations
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The climate is governed by external factors, including the intensity of solar output and volcanic aerosols
and greenhouse gas concentrations
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GREENHOUSE EFFECT?
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ENHANCED GREENHOUSE EFFECT?
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Greenhouse Gases and WarmingCO2
Related?
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SIMULATIONS OF CLIMATE CHANGE
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Natural
1000 1200 1400 1600 1800 2000
Volcanism
Solar
CLIMATE FORCINGS
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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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CLIMATE FORCINGS
Anthropogenic
Greenhouse Gases
Industrial Aerosols
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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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Knutson, T.R., T.L. Delworth, K.W. Dixon, and R.J. Stouffer, Model assessment of regional surface temperature trends (1949-1997), Journal of Geophysical Research, 104, 30981-30996, 1999.
OBSERVED ANNUAL MEAN TREND 1949-1997
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Inconsistent with Natural unforced Variability
Inconsistent with Greenhouse+Sulphate Forcing
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Jones, P.D., Mann, M.E., Climate Over Past Millennia, Reviews of Geophysics, 42, RG2002, doi:10.1029/2003RG000143, 2004.
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Climate Change 2001: The Scientific Basis, Houghton, J.T., et al. (eds.), Cambridge Univ.
Press, Cambridge, 2001
Future Surface Temperatures Trends?
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CONCLUSIONS•Recent global surface temperatures are unprecedented this century, and likely at least the past millennium
•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
•Uncertainties remain regarding the precise sensitivity of the climate to forcing, and the regional details of expected climate changes