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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
`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
`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
`Most of the observed increase in
globally averaged temperatures
since the mid-20th century is very
likely due to the observed increase
in anthropogenic greenhouse gas
concentrations’
Intergovernmental Panel on Climate Change
(United Nations), Fourth Assessment Report, 2007
OBSERVATIONS
Surface Temperature Changes
Gray: back to beginning of 20th century
Boxes: back to mid 19th century
Surface Temperature Changes
Surface Temperature Changes
Internally
Consistent
Changes in
Other Variables
CO2
Related?
Greenhouse
Gases and
Warming
ENHANCED GREENHOUSE EFFECT?
TREE RINGS
CORALS
ICE CORES
VARVED LAKE SEDIMENTS
HISTORICAL DOCUMENTS
RECONSTRUCTED
GLOBAL
TEMPERATURE
PATTERNS
Reconstructed Surface Temperatures
Climate Change 2001: The
Scientific Basis, Houghton, J.T.,
et al. (eds.), Cambridge Univ.
Press, Cambridge, 2001
From “Wikipedia”
Reconstructions of Northern Hemisphere mean temperatures
for the last 1000 years and instrumental record (black line)
Mt Kilimanjaro
Mt Kilimanjaro
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.
MODEL SIMULATIONS
The climate represents a coupled system
consisting of an atmosphere, hydrosphere,
biosphere, and cryosphere
General Circulation
Models (GCMs) take
into account the full
three-dimensional
structure of the
atmosphere and ocean
CLIMATE FORCINGS
Volcanism
1000
1200
1400
1600
1800
Solar
Natural
Crowley, T.J., Causes of
Climate Change Over the
Past 1000 Years, Science,
289 270-277, 2000.
2000
CLIMATE FORCINGS
Anthropogenic
Greenhouse
Gases
Industrial
Aerosols
Climate Change 2001: The
Scientific Basis, Houghton, J.T.,
et al. (eds.), Cambridge Univ.
Press, Cambridge, 2001
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
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
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
Jones, P.D., Mann, M.E., Climate
Over Past Millennia, Reviews of
Geophysics, 42, RG2002,
doi:10.1029/2003RG000143, 2004.
Future Surface Temperatures Trends?
Climate Change 2001: The Scientific Basis, Houghton, J.T.,
et al. (eds.), Cambridge Univ. Press, Cambridge, 2001
Model Predictions
Climate Change 2001: The Scientific Basis, Houghton, J.T.,
et al. (eds.), Cambridge Univ. Press, Cambridge, 2001
Model Predictions