Outline

1. Outline • Climate Change Primer • Causes of the Observed Warming • Projections of Climate Changes and Their Impacts • Abrupt Climate Change – Shutdown of the Atlantic Thermohaline Circulation • Conclusions

2. Conclusions (1 of 4) • The observed warming during 1856-1990 was predominantly human induced. • This and the observed melting of alpine glaciers, the Greenland and West Antarctic Ice Sheets, the freshening of the North Atlantic Ocean, and the slowdown of the Atlantic thermohaline circulation are the “Ozone Hole” of Global Warming. • These observed changes and ongoing research have shown that human-induced warming is proceeding more quickly than anticipated. It is now clear that we have no time to spare - we must act immediately.

3. Conclusions (2 of 4) • Two major factors cause the range of possible future temperature increases: (1) we don’t know precisely how sensitive the climate system will be to future emissions and (2) we don’t know exactly how much humankind will emit. We can only control one of these 2 factors; by reducing emissions, we can reduce the amount of future warming and associated impacts.

4. Conclusions (3 of 4) • If we continue on our present course of increasing emissions, there is a good chance that the warming could be even greater than the IPCC projected high end of 10 degrees F. • If we continue on our present emissions path, there is a high likelihood that the Atlantic thermohaline circulation will be shutdown during the next 200 years. Reducing CO2 emissions reduces this probability significantly.

5. Conclusions (4 of 4) • Our simulation of the geographic distribution of climate change due to such a shutdown shows a very large winter warming over Alaska and over the West Antarctic Ice Sheet. This suggests the “Nightmare” scenario wherein global warming causes the loss of both the Greenland and West Antarctic Ice Sheets, thereby increasing sea level by 40 feet.

6. Nice planet we have. Let’s keep it that way.