1. Future climate (Ch. 19) 1. Enhanced Greenhouse Effect 2. CO 2 sensitivity 3. Projected CO 2 emissions 4. Projected CO 2 atmosphere concentrations 5. What about other gases? 6. Projected T increases

2. anthropogenic increase in CO 2 and CH 4 2000: 365 ppm 1800: 280 ppm 1. Enhanced Greenhouse Effect

3. What will happen to Earth’s climate system as the abundance of greenhouse gases in the atmosphere continue to increase? What we need to know is Earth’s “CO 2 sensitivity”

4. 2. CO 2 sensitivity T changes caused by changing CO 2 abundance by given amount CO 2 sens. = (T change) / (change in CO 2 amount) e.g., for 2 x CO 2 amount, 4 x CO 2 amount

5. CO 2 sensitivity CO 2 sens. = (T change) / (change in CO 2 amount) or T change = (CO 2 sens.) x (change in CO 2 amount) For given CO 2 change: If sensitivity high, T change large If sensitivity low, T change small

6. Equivalent CO 2 a measure of the amount of the combined effect of all greenhouse gases, calculated as if CO 2 were the only greenhouse gas

7. GCM results for CO 2 sensitivity 280 ppm 560 ppm

8. GCM results for CO 2 sensitivity Much variation. Intergovernmental Panel on Climate Change (IPCC, 2007): +2.5 o C for 2 x CO 2 560 ppm280 ppm

9. Q: Why is there so much uncertainty in determining CO 2 sensitivity?

10. Q: Why is there so much uncertainty in determining CO 2 sensitivity? A: Because of feedbacks.

11. T - water vapor feedback

12. T - albedo feedback less snow & ice, lower albedo more absorption of radiation by ground

13. Some feedbacks to CO 2 changes.

14. GCM results for CO 2 sensitivity Curves steeper Curves less steep Why?

15. Q: Can’t we determine CO 2 sensitivity by using recent known temperature and CO 2 changes?

16. Q: Can’t we determine CO 2 sensitivity by using recent known temperature and CO 2 changes? A: Yes, but… We have to consider that response lags behind forcing And consider SO 2 pollution

18. SO 2 + 2H 2 O = H 2 SO 4 + 2H SO 2 released from burning, e.g. S-bearing coal This SO 2 combines with water to make sulfuric acid Get cooling effect & acid rain Effect of SO 2 pollution gas liquid liquid in solution Produces cooling effect in atmosphere-- what book calls “sulfate” aerosol

19. SO 2 pollution and sulfate

21. Global sulfate emissions

22. Temperature variations correlated with SO 2 pollution? 1950-2000 x x x x = major sulfate aerosol sources Average: +0.7 o C/100 yrs

23. Thought experiment illustrating different response times for CO 2 and SO 2

24. Q: Can’t we determine CO 2 sensitivity by using past climate info?

25. Q: Can’t we determine CO 2 sensitivity by using past climate info? A: Yes, to some extent.

26. CO 2 data: ice cores T data: various CO 2 data: vegetation changes T data: various b a a b

27. 3. Projected CO 2 emissions % increase = % increase change change in in C in x in emission x efficiency of emissions population per person of C use

28. Projected CO 2 emissions % increase = % increase change change in in C in x in emission x efficiency of emissions population per person of C use Likely to get higher or lower?

29. max x

30. Projected CO 2 emissions % increase = % increase % change % change in in C in x in emission x efficiency of emissions population per person of C use Likely to get higher or lower?

31. Projected CO 2 emissions % increase = % increase % change % change in in C in x in emission x efficiency of emissions population per person of C use Likely to get higher or lower? Standard of living? C taxes? Cap & trade? Conservation?

32. Projected CO 2 emissions % increase = % increase % change % change in in C in x in emission x efficiency of emissions population per person of C use Likely to get higher or lower?

33. Projected CO 2 emissions % increase = % increase % change % change in in C in x in emission x efficiency of emissions population per person of C use Likely to get higher or lower? Fuel type (oil, gas, bituminous coal, anthracitic coal, oil shale? H??) Technology Wind? Solar? Nuclear? Biofuels?

34. Current trends minimum (from pre-industrial CO 2 value = 280 ppm) Q: Why do curves reach maximum?

35. Current trends minimum (from pre-industrial CO 2 value = 280 ppm) Q: Why do curves reach maximum? A: We run out of fossil fuels

36. 4. Projected CO 2 atmosphere concentration How does Earth redistribute CO 2 ? Some stays in atmosphere Some goes into biomass Some into oceans (over millions of years: into rock) Roughly half of atmosphere value

37. CO 2 only

38. 5. What about other gases? sulfur dioxide SO 2 methane CH 4 concentrations of both will probably go up

39. Melting of methane clathrate ice in deep ocean & in permafrost CH 4

40. 6. Projected temperature increase What should happen on Earth as temperature increases?

41. What should happen on Earth as temperature increases? More evaporation, more rain overall (exceptions!) Cloudier Less glaciers, sea ice, icesheets More forests at high latitudes More plant growth Higher sealevel Changes in habitat Change in season length

42. Assumes mid-range CO 2 sensitivity: +2.5 o C for 2 x CO 2 +5 o C for 4 x CO 2 130 yrs 300 yrs

43. 4 x CO 2 path (likely) could lead in 50-500 to Earth like it was 10-50 Myr ago But… different now in rate at which system changing Use past as guide to the future?

44. IPCC (2007) sea level: +30 cm 2 x CO 2 in year 2100

45. Change in seasons at mid-latitudes

46. 2 x CO 2 scenario at peak warming More change at high latitudes (>40 o ) especially in winter (why?)

47. Sea level: +1 to 2 m 4 x CO 2 Yr 2200-2300 Sea level: +1 to 2 m

48. Bye-bye ice sheets? How quickly to melt?

49. “Estimated future changes in climate will be on a scale comparable to the largest natural changes of the past… We are now ~0.7 o C of the way [out of 2.5-5 o C projected warming] into this huge new experiment in transforming our planet… Unless technology or extreme conservation efforts intervene, Earth is headed toward a warmer future at rates that are unprecedented in its 4.5-billion-year history” --Ruddiman, p. 357