1. Extreme climate in the 21 st century Noah S. Diffenbaugh Department of Environmental Earth System Science and Woods Institute for the Environment Stanford University

2. IPCC SRES Scenarios Raupach et al., 2007 A2: > 800 ppm CO 2 in 2100 Simulations test difference between: 1961-1989 2071-2099

3. General Circulation Model Australia Government BOM

4. Nested High-Resolution Climate Model Driver Variables Temperature Pressure Winds Geopotential Height Specific Humidity Driver variables passed to nested model at lateral boundaries every 6 model hours

5. Walker and Diffenbaugh, 2009 Diffenbaugh and Ashfaq, in review

6. Increases of 100 to 560 % in occurrence and 50 to 550 % in duration Change in Extreme Hot Event Occurrence Diffenbaugh et al., 2005 2071-2099 minus 1961-1989

7. Change in Extreme Cold Events Extreme Cold Frequency Extreme Cold Magnitude 2071-2099 minus 1961-1989 Diffenbaugh et al., 2005

8. Poumadere et al., 2005

9. Magnitude of 2003 Heat Stress Giorgi and Diffenbaugh, 2008 2071-2099 minus 1961-1989

10. Trapp, et al., PNAS, 2007 Change in Severe Thunderstorm Environments Inceases in CAPE overcome decreases in shear

11. Harshvardhan et al., in revision Air Stagnation Events

12. IPCC SRES Scenarios Raupach et al., 2007 A1B Simulation between: 1950-2039 5 ensemble members => physically uniform

13. Ensemble Mean Exceedence of 1951-1999 3-month maximum value Diffenbaugh and Ashfaq, in review

14. Summary and Conclusions High-resolution nested climate models often project larger changes in health-relevant metrics than global climate models. => is this a real feature of the climate system? Near-term (decadal), local-scale climate prediction is of high value as a climate service, but is at best very challenging (and at worst impossible) from a scientific perspective.