PALEOCLIMATE IMPLICATIONS FOR RECENT HUMAN INFLUENCE ON CLIMATE Michael E. Mann Department of Environmental Sciences University of Virginia World Federation of Scientists August 22, 2003

CO2 Concentration Measurements of CO2 in parts per million (ppm) at Mauna Loa Observatory.

Greenhouse Gases and Warming CO2 Related?

PALEOCLIMATOLOGY

PALEOCLIMATOLOGY

PALEOCLIMATOLOGY

Modeled Internal Natural Variability Observations

PALEOCLIMATE ‘PROXY’ DATA

TREE RINGS

CORALS

ICE CORES

VARVED LAKE SEDIMENTS

HISTORICAL DOCUMENTS

Annual Resolution Proxy Climate Indicators INSTRUMENTAL TEMPERATURE RECORD GLOBAL PROXY CLIMATE RECORDS

Reconstructed Surface Temperatures Mann, M.E., Bradley, R.S., Hughes, M.K., Global-Scale Temperature Patterns and Climate Forcing Over the Past Six Centuries, Nature, 392, 779-787, 1998.

Reconstructed Surface Temperatures Climate Change 2001: The Scientific Basis, Houghton, J.T., et al. (eds.), Cambridge Univ. Press, Cambridge, 2001

Temperature Proxy Climate Indicators Past two millennia… Mann, M.E., Jones, P.D., Global Surface Temperatures over the Past Two Millennia, Geophysical Research Letters, in press, 2003.

Temperature Proxy Climate Indicators Past two millennia… Mann, M.E., Ammann, C., Bradley, R.S., Briffa, K., Crowley, T.J., Hughes, M.K., Jones, P.D., Oppenheimer, M., Osborn, T.J., Overpeck, J.T., Rutherford, S., Trenberth, K.E., Wigley, T.M.L., On Past Temperatures and Anomalous late 20th Century Warmth, Eos, in press, 2003.

Northern Hemisphere Reconstructed Surface Temperatures Past two millennia… Northern Hemisphere Mann, M.E., Jones, P.D., Global Surface Temperatures over the Past Two Millennia, Geophysical Research Letters, in press, 2003.

Northern Hemisphere Reconstructed Surface Temperatures Past two millennia… Northern Hemisphere Mann, M.E., Jones, P.D., Global Surface Temperatures over the Past Two Millennia, Geophysical Research Letters, in press, 2003.

Reconstructed Surface Temperatures Mann, M.E., Jones, P.D., Global Surface Temperatures over the Past Two Millennia, Geophysical Research Letters, in press, 2003.

Reconstructed Surface Temperatures Mann, M.E., Jones, P.D., Global Surface Temperatures over the Past Two Millennia, Geophysical Research Letters, in press, 2003.

Natural CLIMATE FORCINGS Volcanism Solar 1000 1200 1400 1600 1800 2000 Volcanism Solar Natural Crowley, T.J., Causes of Climate Change Over the Past 1000 Years, Science, 289 270-277, 2000.

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

Mann, M.E., The Value of Multiple Proxies Science, 297, 1481-1482, 2002.

Mann, M. E. , Ammann, C. , Bradley, R. S. , Briffa, K. , Crowley, T. J Mann, M.E., Ammann, C., Bradley, R.S., Briffa, K., Crowley, T.J., Hughes, M.K., Jones, P.D., Oppenheimer, M., Osborn, T.J., Overpeck, J.T., Rutherford, S., Trenberth, K.E., Wigley, T.M.L., On Past Temperatures and Anomalous late 20th Century Warmth, Eos, in press, 2003.

Future Surface Temperatures Trends? Climate Change 2001: The Scientific Basis, Houghton, J.T., et al. (eds.), Cambridge Univ. Press, Cambridge, 2001

CONCLUSIONS Comparisons between different proxy-based estimates, model predictions, and optimally- determined borehole estimates of past hemispheric SAT trends indicate broad consistency over the past millennium. The latest results indicate that late 20th warmth appears unprecedented over at least the past two millennia for the Northern Hemisphere; conclusions for the Southern Hemisphere and globe are presently indeterminate.