Future climate (Ch. 19) 1. Enhanced Greenhouse Effect 2. CO 2 sensitivity 3. Projected CO 2 emissions 4. Projected CO

1. Future climate (Ch. 19) 1. Enhanced Greenhouse Effect 2. CO2 sensitivity 3. Projected CO2 emissions 4. Projected CO2 atmosphere concentrations 5. What about other gases? 6. Projected T increases

2. 2000: 365 ppm 1. Enhanced Greenhouse Effect 1800: 280 ppm anthropogenic increase in CO2 and CH4

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 “CO2 sensitivity”

4. 2. CO2 sensitivity T changes caused by changing CO2 abundance by given amount CO2 sens. = (T change) / (change in CO2 amount) e.g., for 2 x CO2 amount, 4 x CO2 amount

5. CO2 sensitivity CO2 sens. = (T change) / (change in CO2 amount) or T change = (CO2 sens.) x (change in CO2 amount) For given CO2 change: If sensitivity high, T change large If sensitivity low, T change small

6. Equivalent CO2 a measure of the amount of the combined effect of all greenhouse gases, calculated as if CO2 were the only greenhouse gas

7. GCM results for CO2 sensitivity 560 ppm 280 ppm

8. GCM results for CO2 sensitivity Much variation. Intergovernmental Panel on Climate Change (IPCC, 2007): +2.5 oC for 2 x CO2 280 ppm 560 ppm

9. Q: Why is there so much uncertainty in determining CO2 sensitivity?

10. Q: Why is there so much uncertainty in determining CO2 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 CO2 changes.

14. GCM results for CO2 sensitivity Curves less steep Why? Curves steeper

15. Q: Can’t we determine CO2 sensitivity by using recent known temperature and CO2 changes?

16. Q: Can’t we determine CO2 sensitivity by using recent known temperature and CO2 changes? A: Yes, but… We have to consider that response lags behind forcing And consider SO2 pollution

18. Effect of SO2 pollution • SO2 released from burning, e.g. S-bearing coal • This SO2 combines with water to make • sulfuric acid • Get cooling effect & acid rain SO2 + 2H2O = H2SO4 + 2H gas liquid liquid in solution Produces cooling effect in atmosphere-- what book calls “sulfate” aerosol

19. SO2 pollution and sulfate

21. Global sulfate emissions

22. Temperature variations correlated with SO2 pollution? x x x 1950-2000 Average: +0.7 oC/100 yrs x = major sulfate aerosol sources

23. Thought experiment illustrating different response times for CO2 and SO2

24. Q: Can’t we determine CO2 sensitivity by using past climate info?

25. Q: Can’t we determine CO2 sensitivity by using past climate info? A: Yes, to some extent.

26. a CO2 data: vegetation changes T data: various b b a CO2 data: ice cores T data: various

27. 3. Projected CO2 emissions % increase = % increase change change in in C in x in emission x efficiency of emissions population per person of C use

28. Projected CO2 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 max

30. Projected CO2 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 CO2 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 CO2 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 CO2 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 (from pre-industrial CO2 value = 280 ppm) Q: Why do curves reach maximum? minimum

35. Current trends (from pre-industrial CO2 value = 280 ppm) Q: Why do curves reach maximum? A: We run out of fossil fuels minimum

36. 4. Projected CO2 atmosphere concentration • How does Earth redistribute CO2? • Some stays in atmosphere • Some goes into biomass • Some into oceans • (over millions of years: into rock) Roughly half of atmosphere value

37. CO2 only

38. 5. What about other gases? sulfur dioxide SO2 methane CH4 concentrations of both will probably go up

39. CH4 Melting of methane clathrate ice in deep ocean & in permafrost

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 CO2 sensitivity: +2.5 oC for 2 x CO2 +5 oC for 4 x CO2 300 yrs 130 yrs

43. Use past as guide to the future? 4 x CO2 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

44. 2 x CO2 in year 2100 IPCC (2007) sea level: +30 cm

45. Change in seasons at mid-latitudes

46. 2 x CO2 scenario at peak warming More change at high latitudes (>40 o) especially in winter (why?)

47. 4 x CO2 Yr 2200-2300 Sea level: +1 to 2 m 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 oC of the way [out of 2.5-5 oC 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