The Modeling of Climate and Climate Change; can we trust model predictions?

1. The Modeling of Climate and Climate Change;can we trust model predictions? University of California, Irvine 21 February 2003 by John Houghton

2. Outline • Introduction • Cloud Radiation Feedback • Ocean Interactions • The Carbon Cycle • The Climate of the 20th Century • Climate Projections for the 21st Century • Regional Climate Modeling • Patterns of Climate Response

3. The greenhouse effect Solar radiation Long-wave radiation 236 Wm-2 236 Wm-2 Equivalent T = 255 K (-18ºC) 390 Wm-2 T = 255 K (-15ºC)

4. Spectra of outgoing radiation from Earth observed by IRIS on Nimbus 3

6. The Enhanced Greenhouse Effect S L 236 236 S L 236 232 S L 236 236 S L 236 236 Solar (S) and longwave (L) radiation in Wm-2 at the top of the atmosphere T = -18°C CO2 x 2 + Feedbacks H2O (+60%) Ice/Albedo (+20%) Cloud? Ocean? CO2 x 2 CO2 x 2 TS = 15°C TS = 15°C DTS ~ 1.2K DTS ~ 2.5K

7. The climate system

8. The Development of Climate models, Past, Present and Future Mid 1980s Early 1990s Late 1990s Present day Early 2000s? Mid 1970s Atmosphere Atmosphere Atmosphere Atmosphere Atmosphere Atmosphere Land surface Land surface Land surface Land surface Land surface Ocean & sea-ice Ocean & sea-ice Ocean & sea-ice Ocean & sea-ice Sulphate aerosol Sulphate aerosol Sulphate aerosol Non-sulphate aerosol Non-sulphate aerosol Carbon cycle Carbon cycle Atmospheric chemistry Sulphur cycle model Non-sulphate aerosols Ocean & sea-ice model Off-line model development Strengthening colours denote improvements in models Land carbon cycle model Carbon cycle model Ocean carbon cycle model Atmospheric chemistry Atmospheric chemistry

9. Predicting impacts of climate change Scenarios from population, energy, economics models Emissions Concentrations CO2, methane, sulphates, etc. Global climate change Temperature, rainfall, sea level, etc. Regional detail Mountain effects, islands, extreme weather, etc. Impacts Flooding, food supply, etc. Carbon cycle and chemistry models Coupled global climate models Regional climate models Impacts models The main stages required to provide climate change scenarios for assessing the impacts of climate change. Hadley Centre - PRECIS brochure

10. Coupled atmosphere / ocean climate model Radiation Atmosphere: Density Motion Water Heat Exchange of: Momentum Water Ocean: Density (inc. Salinity) Motion Sea Ice Land

12. 30km 19 levels in atmosphere 2.5 lat 3.75 long THE HADLEYCENTRETHIRDCOUPLEDMODEL -HadCM3 1.25 1.25 20 levelsin ocean -5km

14. Physical Feedbacks • Water vapour • Ice albedo • Clouds • Oceans • Ice sheets

15. Cloud Radiation Feedback

16. Cloud radiation feedback

17. Global average change in T /C

18. Model Estimates of Cloud Radiative Forcing with CO2 Doubling

19. Effect of cloud feedback formulation on climate prediction • Feedback scheme Global Av Temp change,C for doubled CO2 • RH 5.3 • CW 2.8 • CWRP 1.9 • after Senior & Mitchell, Hadley Centre

20. Net cloud forcing: January to July Hadley Centre

21. SHIP TRACKS UNDER CLOUD Washington state

22. Ocean Interactions

23. IPCC Synthesis Report

24. Strength of the thermohaline circulation in the North Atlantic. Hadley Centre

25. Modelled transport of water in Atlantic conveyor belt IPCC Third Assessment Report

26. Projected changes in annual temperatures for the 2050s The projected change in annual temperatures for the 2050s compared with the present day, when the climate model is driven with an increase in greenhouse gas concentrations equivalent to about 1% increase per year in CO2 BW 11 The MetOffice. Hadley Center for Climate Prediction and Research.

27. Changes in surface air temperature, relative to the present day, 20 years after the hypothetical collapse of the thermohaline circulation. Hadley Centre

28. Combined effect of THC collapse (2049-2059) and global warming Surface Temperature Cooling over UK: 1-3°C

29. The Carbon Cycle

31. IPCC Third Assessment Report

32. Human Perturbation of the Carbon Cycle

33. Partitioning of CO2 uptake using O2 measurements

34. Global CO2 budgets in GtC per year 1980s 1990s Atmospheric increase 3.3 ± 0.1 3.2 ± 0.1 Emissions (fossil fuel, cement) 5.4 ± 0.3 6.3 ± 0.4 Ocean-atmosphere flux -1.9 ± 0.6 -1.7 ± 0.5 Land atmosphere flux -0.2 ± 0.7 -1.4 ± 0.7 partitioned as follows: Land-use change 1.7 (0.6 to 2.5) NA Residual terrestrial sink -1.9 (-3.8 to 0.3) NA IPCC Third Assessment Report

35. Carbon cycle feedbacks

36. Change in carbon content of soil (top) and vegetation (bottom) between 1860 and 2100 - predicted by Hadley Centre climate model Hadley Centre

37. Simulated changes in the global total soil and vegetation carbon content (Gt C) between 1860 and 2100. Hadley Centre

38. Influence of ENSO on CO2 Variability • Annual changes in atmospheric CO2 are dominated by ENSO • after removing anthropogenic rise • rise during El Nino • fall during La Nina CO2 - black, Nino3 - red

39. Influence of Volcanoes on CO2 Variability • 2 notable exceptions to ENSO correlation • CO2 levels lower than expected • Coincide with major volcanic eruptions El Chichon Pinatubo CO2 - black, Nino3 - red

40. Constraint from ENSO Sensitivity • Model with q10=2 has realistic sensitivity to ENSO. • Reconstructions for range of q10. • Infer q10=2.1±0.7.

41. Constraint from Sensitivity to Volcanoes • Model with q10=2 has realistic sensitivity to Pinatubo. • Reconstructions for range of q10. • Infer q10=1.9±0.4

42. ENSO and Pinatubo Variations as a constraint on climate-carbon cycle feedback Model with C cycle Feedback (q10= 2) Grey region is estimate of uncertainty related to q10 parameter for soil respiration Model without C cycle Feedback q10= 3 q10= 1

43. Photo: Tim Hewison

44. Estimated carbon uptake if suitable arable land north of 30º N were to be replaced with trees. The additional effect on climate of the changes in surface reflectivity when trees are planted on suitable arable land north of 30º N, expressed as equivalent carbon emissions. The difference between the two diagrams above. Negative values show where the net effect of planting trees is to warm climate. Hadley Centre

45. NET EFFECT OF PLANTING TREESexpressed as equivalent carbon uptake – 50 0 50 100 150 200 tonnes of carbon per hectare Met Office / Hadley Centre Negative values show where the net effect of planting trees is to warm climate

46. 20 1000 950 900 850 15 emissions (GtC/yr) 800 750 700 CO concentration (ppm) 10 2 650 600 2 Anthropogenic CO 550 5 500 450 400 0 350 2000 2050 2100 2150 2200 2250 2300 2350 2000 2050 2100 2150 2200 2250 2300 2350 750 ppm stabilisation 550 ppm stabilisation Unmitigated emissions EMISSIONS AND CONCENTRATIONS OF CO2from unmitigated and stabilising emission scenarios Source: IPCC

47. The Climate of the 20th Century

48. Global mean surface air temperature anomalies from 1,000 year control simulations with three different climate models, - Hadley, GFDL and Hamburg, compared to the recent instrumental record. No model control simulation shows a trend in surface air temperature as large as the observed trend. If internal variability is correct in these models, the recent warming is likely not due to variability produced within the climate system alone. IPCC Third Assessment Report

49. Simulated annual global mean surface temperatures Natural forcing Anthropogenic forcing

50. Simulated annual global mean surface temperatures