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“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
General Circulation Model (“GCM”) Laws of Physics!!! Australia Government BOM
Two basic parts: • “Dynamics” • Atmospheric circulation • Ocean circulation • “Physics” • Radiation • Clouds • Precipitation • Land surface fluxes • and more…..
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
Observed and Modeled Water Vapor Content • important for greenhouse effect • important for atmospheric circulation • important for extreme events Santer et al., 2007
Keeling Curve Global Warming Art
IPCC, 2007 • Observed warming does not occur without human forcings
IPCC SRES Scenarios Raupach et al., 2007
• spread within each scenario • spread between scenarios IPCC, 2007
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
“Internal Variability” “Model” “Scenario” Hawkins and Sutton, 2009
Date of permanent exceedence of late-20th century maximum Diffenbaugh and Scherer, 2011
U.S.A. Summer Soil-Moisture/Temperature/Precipitation Coupling 2030-2039 minus 1980-1999 Diffenbaugh and Ashfaq, 2010
Joplin Tornado – May 22, 2011 CBS News
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
Climate Change Uncertainty Giorgi, Diffenbaugh, et al., 2008
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?