Extreme climate in the 21st century

Noah S. Diffenbaugh

Department of Environmental Earth System Science

and

Woods Institute for the Environment

Stanford University

IPCC SRES Scenarios

Raupach et al., 2007

A2: > 800 ppm CO2 in 2100

Simulations test difference between:

1961-1989

2071-2099

General Circulation Model

Australia Government BOM

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

Walker and Diffenbaugh, 2009

Diffenbaugh and Ashfaq, in review

• Increases of 100 to 560 % in occurrence and 50 to 550 % in duration

Change in Extreme Hot Event Occurrence

Diffenbaugh et al., 2005

2071-2099minus

1961-1989

Change in Extreme Cold Events

∆ Extreme Cold Frequency ∆ Extreme Cold Magnitude

2071-2099minus

1961-1989Diffenbaugh et al., 2005

Poumadere et al., 2005

Magnitude of 2003

Heat Stress

Giorgi and Diffenbaugh, 2008

2071-2099minus

1961-1989

Trapp, et al., PNAS, 2007

Change in Severe Thunderstorm Environments

• Inceases in CAPE overcome decreases in shear

Harshvardhan et al., in revision

Air Stagnation Events

IPCC SRES Scenarios

Raupach et al., 2007

A1B

Simulation between:

1950-2039

5 ensemble members=> “physically uniform”

Ensemble Mean

• Exceedence of 1951-1999 3-month maximum value

Diffenbaugh and Ashfaq, in review

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.