1. Climate Change and Global Warming Michael E. Mann Department of Environmental Sciences University of Virginia Waxter Environmental Forum Sweet Briar College March 14, 2002

2. `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

3. THE EMPIRICAL RECORD

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

5. Shaded: 20 th century Boxes: since mid 19 th century Surface Temperature Changes

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

7. 1998 Global Temperature Pattern

8. EL NINO/SOUTHERN OSCILLATION (“ENSO”) Multivariate ENSO Index (“MEI”) Substantial interannual climate variability associated with ENSO, but decadal variability is also evident as well. The recent decadal trend towards El Nino conditions could be natural or anthropogenic.

9. NORTH ATLANTIC OSCILLATION Negative Phase Positive Phase

10. This NAO trend could be Anthropogenic NORTH ATLANTIC OSCILLATION

11. “PACIFIC DECADAL OSCILLATION”

12. There is evidence of multidecadal natural variability in the North Atlantic ocean circulation Atlantic Multidecadal Oscillation

13. Greenhouse Gases and Warming CO 2 Related?

14. TREE RINGS

15. CORALS

16. ICE CORES

17. VARVED LAKE SEDIMENTS

18. HISTORICAL DOCUMENTS

19. RECONSTRUCTED GLOBAL TEMPERATURE PATTERNS

21. “Little Ice Age” European Winter Cooling During the Little Ice Age

22. LIA winter cooling in Europe associated with an NAO trend due to solar irradiance changes, interacting w/ stratospheric atmospheric dynamics and chemistry Empirical NASA/GISS Model European Winter Cooling During the Little Ice Age Shindell, D.T., Schmidt, G.A., Mann, M.E., Rind, D., Waple, A., Solar forcing of regional climate change during the Maunder Minimum, Science, 294, 2149- 2152, 2001.

23. CLIMATE MODELS

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

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

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

27. Modeled Internal Natural VariabilityObservations

28. INFLUENCE OF EXTERNAL FACTORS

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

30. Solar Variations

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

32. Volcanoes

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

35. GREENHOUSE EFFECT?

37. ENHANCED GREENHOUSE EFFECT?

38. Greenhouse Gases and Warming CO 2 Related?

39. SIMULATIONS OF CLIMATE CHANGE

40. Natural 100012001400160018002000 Volcanism Solar CLIMATE FORCINGS

41. 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

42. CLIMATE FORCINGS Anthropogenic Greenhouse Gases Industrial Aerosols

43. 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

44. 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

45. 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

46. Science Energy Balance Model (“EBM”) simulation

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

48. 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 Uncertainties remain regarding the precise sensitivity of the climate to forcing, and the regional details of expected climate changes