Global Climate Change: Past and Future Michael E. Mann Departments of Meteorology and Geosciences and Earth and Environmental Systems Institute (EESI) Penn State University Pennsylvania Consortium for Interdisciplinary Environmental Policy and the Pennsylvania Environmental Council Harrisburg PA Oct 5, 2006

`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

THE DATA

Surface Temperature Changes Climatic Research Unit (‘CRU’), University of East Anglia

Greenhouse Gases and Warming CO2 Related?

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HISTORICAL DOCUMENTS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

Thompson, L. G. , Mosley-Thompson, E. , Davis, M. E. , Lin, P. N 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.

From “Wikipedia” Reconstructions of Northern Hemisphere mean temperatures for the last 1000 years and instrumental record (black line)

CLIMATE MODELS

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

January Temp (observations) GCMs do a fairly good job of describing the seasonal cycle in surface temperature January Temp (model) This alone doesn’t guarantee that they should do a good job in describing climate change!

INFLUENCE OF EXTERNAL FACTORS

The climate is governed by external factors, including the intensity of solar output and volcanic aerosols and greenhouse gas concentrations

Solar Variations

Solar Variations

The climate is governed by external factors, including the intensity of solar output and volcanic aerosols and greenhouse gas concentrations

Volcanoes 1000 1200 1400 1600 1800 2000

The climate is governed by external factors, including the intensity of solar output and volcanic aerosols and greenhouse gas concentrations

GREENHOUSE EFFECT?

ENHANCED GREENHOUSE EFFECT?

ANTHROPOGENIC IMPACTS Industrial Aerosols Greenhouse Gases Climate Change 2001: The Scientific Basis, Houghton, J.T., et al. (eds.), Cambridge Univ. Press, Cambridge, 2001

SIMULATIONS OF CLIMATE CHANGE

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

Possible Impacts? Climate Change 2001: The Scientific Basis, Houghton, J.T., et al. (eds.), Cambridge Univ. Press, Cambridge, 2001

Gavin Schmidt, Michael Mann David Archer, Ray Pierrehumbert ``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