1. 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

2. `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

3. `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

4. THE DATA

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

6. Greenhouse Gases and Warming
CO2
Related?

7. TREE RINGS

8. CORALS

9. ICE CORES

10. VARVED LAKE SEDIMENTS

11. HISTORICAL DOCUMENTS

12. RECONSTRUCTED GLOBAL TEMPERATURE PATTERNS

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

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

15. CLIMATE MODELS

16. The climate represents a coupled system consisting of an atmosphere, hydrosphere, biosphere, and cryosphere

17. General Circulation Models take into account the full three-dimensional structure of the atmosphere and ocean

18. 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!

19. Modeled Internal Natural Variability
Observations

20. INFLUENCE OF EXTERNAL FACTORS

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

22. Solar Variations

23. Solar Variations

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

25. Volcanoes

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

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

28. ENHANCED GREENHOUSE EFFECT?

29. SIMULATIONS OF CLIMATE CHANGE

30. 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

31. 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

32. 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

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

34. North American Drought
Possible Impacts:
North American Drought

35. 1998 Global Temperature Pattern

36. El Nino and North American Drought

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

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

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

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

41. 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, , 2005.

42. Hurricane Statistics
Emanuel, K. (2005), Increasing destructiveness of tropical cyclones over the past 30 years, Nature, online publication; published online 31 July 2005 | doi: /nature03906

43. 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),

44. 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

45. 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