Global Climate Change: Past and Future Michael E. Mann Department of Meteorology and Earth and Environmental Systems Institute (EESI) Penn State University University of California at Santa Cruz May 10, 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HISTORICAL DOCUMENTS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

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 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!

Modeled Internal Natural Variability Observations

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

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

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

ENHANCED GREENHOUSE EFFECT?

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

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

North American Drought Possible Impacts: North American Drought

1998 Global Temperature Pattern

El Nino and North American Drought

El Nino vs. North American Drought over the Past Century Increased Drought La Nina El Nino Less Drought Courtesy of E.Cook

Destructive Potential of Atlantic Hurricanes Possible Impacts: Destructive Potential of Atlantic Hurricanes Katrina (Aug 28 ’05)

Destructive Potential of Atlantic Hurricanes Possible Impacts: Destructive Potential of Atlantic Hurricanes Rita (Sep 21 ’05)

Destructive Potential of Atlantic Hurricanes Possible Impacts: Destructive Potential of Atlantic Hurricanes Wilma (Oct 19 ’05)

Hurricane Statistics P. J. Webster, G. J. Holland, J. A. Curry, H.-R. Chang Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment, Science, 309, Issue 5742, 1844-1846 , 2005.

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

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.

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 Possible impacts of anthropogenic climate change this century include increased drought conditions in the western U.S. and more destructive Atlantic tropical storms and Hurricanes

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