1. Man Made Climate Change vs. Natural Variability Presented By: Mark Seaman Sam Atwood EESC W4400

2. 2 Benin Natural Variability in the Climate System Long-Term: Glacial / Interglacial Periods Variability over 10s to 100s of thousands of years Max ~ 4°C to 6°C change over a Glacial / Interglacial cycle Variations in Orbit, and Ice Sheet Cover and other Feedbacks Short-Term: Last several Millennia Max +/- 0.2°C change over a century Solar Irradiance and Volcanism Not constant on all time or spatial scales “Little Ice Age” and “Medieval Warm Period” Source: Jones, P.D., and M.E. Mann (2004)

3. 3 Anthropogenic Impact on Climate System Typical natural range of variability exceeded in 20th Century +0.6 to +0.9°C change Man Made Forcings Physically understood mechanisms Greenhouse Gas Levels Climate Sensitivity: 1.5°C to 4.5°C with doubling of CO 2 Sulfate Aerosols Land Use Changes Last half of 20th Century Anthropogenic impacts dominate over Natural Variability Source: Jones, P.D., and M.E. Mann (2004)

4. 4 Temperature Variations in Last Millennium Source: IPCC Climate change 2001 - Synthesis report

5. 5 Primary Take Home Points Man Made Climate Change is different from Natural Variability in the Climate System This difference: Timescale: The time of the change is quicker Spatial scale: Mean trends for the entire planet Magnitude: The direction and amount of change Questions?