Tom Ackerman Professor, Department of Atmospheric Sciences

1. Tom AckermanProfessor, Department of Atmospheric Sciences

2. Planet Earth has warmed over the last 100 years

3. Data analyzed by Hadley Research Centre, United Kingdom

5. Probable CauseIncrease in greenhouse gas concentrations

6. Pre-industrial level

8. Atmosphere Carbon balance Fossil fuel emission 6.1 GTon / year Deforestation 1.5 GTon /year Total ~7.5 GT / year Increasing CO2 in atmosphere 3 GT / year Uptake in mixed layer 2.5 GT / year Reforestation in NA 0.5 GT / year Total ~ 6 GT / year

9. The Facts • Surface temperature is increasing • Increase is unprecedented in last 1000 years (and probably more) • CO2 is on the rise – up about 35% • About 20% of the CO2 emission cannot be accounted for at present! • Increasing CO2 causes increasing surface temperature

10. Okay, so the question is:What’s going to happen to global climate over the next 10 to 50 years? Corollary:How would we know?

11. Let’s build a CLIMATE model!

12. What do we need in our climate model? Atmosphere H2O vapor and Clouds Absorbing gases – CO2 Aerosol Biota Surface vegetation Ice Sea ice Ice sheets (glaciers) Ocean

13. Complete 4D model Coordinates: Latitude Longitude Height Time

14. Constructing a climate model • Decide on the variables – what do we want to predict? • T, wind speed (3D), water vapor concentration • Write down time-dependent equations Temp (time = t + t) = Temp (time = t) + (all the things that change the temperature) • Can’t solve these equations exactly

16. How big is big? 300 km x 300 km Typical values for current ATMOSPHERE ONLY climate models 5 variables (minimum) 8190 boxes 26 vertical levels 30 minute time step (48/day) 51.1 million equations / day 18.6 billion equations / year

17. Climate modeling challenges the biggest computers CRAY Japanese Earth Simulator IBM Blue Sky (NCAR)

18. Let’s RUN our climate model!

19. How to run a climate model Prescribed forcing (Sun, CO2, etc.) Initial conditions Run forward in time for at least 10 to 30 years Coupled Global Climate Model Atmosphere Ocean Compare averaged model results with averaged climate results

20. Major questions • Can we simulate climate change over the past 100 years? • Is it possible that the current increase in temperature is a result of natural variability in the climate system?

21. Simulating the last 150 years • Input natural forcing into climate model • Volcanic aerosol • Solar activity • Input anthropogenic forcing • CO2 and other greenhouse gases • Sulfate aerosol • Input both

25. IPCC Conclusion In the light of new evidence and taking into account the remaining uncertainties, most of the observed warming over the last 50 years is likely to be due to the increases in greenhouse gas concentrations.

26. Predicting the future

27. Intergovernmental Panel on Climate Change (IPCC) – est. 1988

28. IPCC is an assessment activity – it does not sponsor research or monitor climate

29. Information chain leading to a climate projection

30. Projecting the future: Scenarios • Estimate future emissions of greenhouse gases and pollutants • CO2 • Other greenhouse gases • Aerosol (sulfate, carbon)

31. Rate of increase in CO2 due to emissions: 73 – 03 1.5 ppmv / year 93 – 03 1.8 ppmv / year Assumption: we can tolerate a climate change corresponding to 600 ppmv • Question: • How many years will it take to reach 600 ppmv at an emission rate of 1.5 ppmv / year?

32. Currently (2004) at 377 ppmv • Amount of extra CO2: 600 – 377 = 223 ppmv • Length of time to accumulate = amount / rate = 223 ppmv / (1.5 ppmv / year) = 149 years

33. Rate of increase in CO2 due to emissions: 73 – 03 1.5 ppmv / year 93 – 03 1.8 ppmv / year Assumption: we can tolerate a climate change corresponding to 600 ppmv • Questions: • How many years will it take to reach 600 ppmv at an emission rate of 1.5 ppmv / year? = 149 years • At an emission rate of 1.8 ppmv / year? = 124 years • So what are we worried about?

34. IPCC Scenarios A1: A world of rapid economic growth and rapid introductions of new and more efficient technologies A2: A very heterogenous world with an emphasis on familiy values and local traditions B1: A world of „dematerialization“ and introduction of clean technologies B2: A world with an emphasis on local solutions to economic and environmental sustainability IS92a „business as usual“ scenario (1992)

35. Emissions scale with population Population increases exponentially (not linearly) Emissions increase exponentially (not linearly)

36. Summary: Scenarios • CO2 concentrations in this century vary widely depending on assumptions about technology use and energy mix • By 2100, we could have CO2 concentrations exceeding 900 ppmv; hard to see how we would have less than ~ 500 ppmv

37. So now let’s put those CO2 estimates into our climate model(“force” our model with CO2)

38. Start of Lecture 2

39. Where we are … • “Built” a climate model • Used the climate model to simulate last 150 years – did a pretty good job • Developed scenarios for the future – based on projected energy use • Started to look at climate change over this during this century

40. IPCC Scenarios A1: A world of rapid economic growth and rapid introductions of new and more efficient technologies A2: A very heterogenous world with an emphasis on familiy values and local traditions B1: A world of „dematerialization“ and introduction of clean technologies B2: A world with an emphasis on local solutions to economic and environmental sustainability IS92a „business as usual“ scenario (1992)

41. Figure SPM-5 Updated: 13 Feb 2007

42. Figure SPM-6

44. Sea level rise

49. “Commitment” Even if we stopped emitting CO2 today, we are committed to more warming and more sea level rise because we have to wait for the climate system to come into equilibrium with the current atmospheric concentration of CO2

50. Summary of effects (very certain) • The globally averaged surface temperature is projected to increase by 1.4 to 5.8°C by 2100. • The projected rate of warming is much larger than the observed changes during the 20th century and is very likely to be without precedent during at least the last 10,000 years. • Global mean sea level is projected to rise by 0.1 to 0.9 meters between 1990 and 2100. • Global mean surface temperature increases and rising sea level from thermal expansion of the ocean are projected to continue for hundreds of years after stabilisation of greenhouse gas concentrations (even at present levels) • Could be more if ice sheets experience catastrophic failure