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  1. “what a climate model is, and what uncertainty means” Noah S. Diffenbaugh Department of Environmental Earth System Science and Woods Institute for the Environment Stanford University

  2. “what a climate model is”

  3. General Circulation Model (“GCM”) Laws of Physics!!! Australia Government BOM

  4. Two basic parts: • “Dynamics” • Atmospheric circulation • Ocean circulation • “Physics” • Radiation • Clouds • Precipitation • Land surface fluxes • and more…..

  5. Global Radiation Balance

  6. Te = [S0(1-ap) / 4σ] 1/4 Te = emission temp S0 = solar “constant” ap = planetary albedo σ = Stefan-Boltzman constant From Marshall and Plumb, Elsevier, 2008

  7. Water Vapor in Air

  8. Observed and Modeled Water Vapor Content • important for greenhouse effect • important for atmospheric circulation • important for extreme events Santer et al., 2007

  9. Atmosphere and Ocean Circulation

  10. “and what uncertainty means”

  11. Observed “Global Warming”

  12. Keeling Curve Global Warming Art

  13. IPCC, 2007 • Observed warming does not occur without human forcings

  14. “The Future”

  15. From the perspective of climate model experiments

  16. IPCC SRES Scenarios Raupach et al., 2007

  17. • spread within each scenario • spread between scenarios IPCC, 2007

  18. Climate Feedbacks Santer et al., 2007 http://internationalspacestationpictures.com/pictures-of-earth-from-space.php NASA http://internationalspacestationpictures.com/pictures-of-earth-from-space.php

  19. “Internal Variability” “Model” “Scenario” Hawkins and Sutton, 2009

  20. Diffenbaugh and Scherer, 2011

  21. Date of permanent exceedence of late-20th century maximum Diffenbaugh and Scherer, 2011

  22. U.S.A. Summer Soil-Moisture/Temperature/Precipitation Coupling 2030-2039 minus 1980-1999 Diffenbaugh and Ashfaq, 2010

  23. Joplin Tornado – May 22, 2011 CBS News

  24. Brooks et al. 2003

  25. Severe Thunderstorm Environments • Vertical Wind Shear • Convective Available Potential Energy (CAPE) Pole-equator temperature gradient S6 Thermal Wind Equation Trapp et al., 2007 Brooks et al., 2003

  26. Trapp et al., PNAS, 2007

  27. From the perspective of the climate system

  28. Climate Change Uncertainty Giorgi, Diffenbaugh, et al., 2008

  29. How do we make decisions when: 1. we don’t know the level of climate forcing in the future? 2. we don’t understand every process that could be important for climate change impacts? 3. The phenomena that matter most for climate change impacts may exceed the limits of predictability?