1. Global Warming: The Debate Objectives: Define the uncertainties Describe the scientific process Analyze available data Explore solutions

2. Four debates 1)Is the climate changing? 2)Are humans responsible? 3)How severe will it be? 4)What should we do about it? Science Science/Policy Policy

3. Why trust science? The scientific method: Theory  Law Carbon dioxide is increasing Is the world getting warmer? The world is warmer today than in 1750 Measure tree rings, ice cores Yes, tree rings and thermometers show a warming trend

4. Why trust science? 1)The scientific method is objective 2)Science is peer-reviewed by experts 3)Ideas are funded, not particular answers

5. Science funding Taxpayer Congress Gov’t Agency Peer Review Scientist Results Private foundationBusiness Scientific Method Peer Review

6. The Intergovernmental Panel on Climate Change (IPCC)

7. The Greenhouse Effect (Fourier 1824) Sunlight Heat Greenhouse gases Sunlight warms the earth The earth cools by radiating heat Greenhouse gases in atmosphere trap heat and re-radiate it back to surface Slide from M. S Torn, LBL

8. 1. Is the climate changing? YES

9. Climategate Issues: data manipulation and sharing –Tree ring data do not match thermometers –No evidence that data were altered –Evading and disparaging skeptics is counterproductive Public is losing confidence in climate science Michael Mann Phil Jones

10. Temperature has risen by 1.5 °F over land 9 of the hottest years of the century occurred in last 10 years

11. CO 2 concentrations are rising Charles David Keeling 2. Are humans responsible? YES

12. Can warming be explained by natural causes? No. Climate Model Simulations:  (a) with only natural processes (solar, volcanoes)  (b) with also anthropogenic gases and aerosols

13. Major Findings of IPCC-4 “Unequivocal” that Earth’s climate is warming Greenhouse gases at highest levels in 650,000 years “Very Likely” that increased greenhouse gases have caused most of the rise in temperatures since 1950

14. 3. How severe will climate change be? It depends… California, relative to last three decades:

15. Expect a lot of change relative to the past:

16. Impacts on the biosphere: feedback loops CO 2 Plant Growth Warming NutrientsDecomposition Negative Positive

17. Temperature increase by 2100 Soil carbon

18. Warming experiment Alaskan boreal forest

19. Measuring soil carbon loss

20. Warming reduces microbial activity

21. We find negative feedbacks CO 2 Plant Growth Warming NutrientsDecomposition Negative Positive

22. Different results in permafrost: Big soil carbon losses

23. Also consider ocean feedbacks

24. 4. What can we do? Mitigate = slow the rate of increase of greenhouse gases Adapt = change infrastructure to deal with climate change Manage = actively manage climate and atmospheric composition Increasing knowledge required

25. Mitigation options Pacala and Socolow, 2004

26. Mitigation options Pacala and Socolow, 2004

27. Mitigation options Pacala and Socolow, 2004

28. Summary Climate change is happening Humans are the likely cause The biosphere may respond in unpredictable ways There are options to avoid climate change