Introduction to Climate Change Scenario Development

1. Introduction to Climate Change Scenario Development Dr. Elaine Barrow CCIS Principal Investigator (Science)

2. What is a climate change scenario? Definitions: “…a coherent, internally consistent and plausible description of a possible future state of the world…” [Parry & Carter, 1998] “…a plausible future climate that has been constructed for explicit use in investigating the potential consequences of anthropogenic climate change…” [IPCC TAR, 2001]

3. A climate scenario is not a prediction of future climate!

4. Why do we need climate change scenarios? • To provide data for VIA assessment studies • To act as an awareness-raising device • To aid strategic planning and/or policy formation • To scope the range of plausible futures • To structure our knowledge (or ignorance) of the future • To explore the implications of decisions

5. Key component of a framework for conducting integrated assessment of climate change for policy applications

6. What are the challenges of developing climate scenarios? • simple to obtain, interpret and apply • provide sufficient information for VIA assessments • physically plausible and spatially compatible • consistent with the broad range of global warming projections • reflect the potential range of future regional climate change, i.e., be representative of the range of uncertainty in projections

7. What you want … … typically is daily weather for a particular place for some future year

8. Three ways ... COMPLEXITY • Incremental (arbitrary, synthetic) scenarios • Analogue scenarios • Scenarios from global climate models (GCMs)

9. T=2°C Incremental Scenariosfor sensitivity studies Can provide valuable information about: • sensitivity • thresholds or discontinuities of response • tolerable climate change

10. ADVANTAGES: simple to construct and apply, allow relative sensitivity of impacts sectors/models to be explored DISADVANTAGES: arbitrary (and unrealistic) changes, may be inconsistent with uncertainty range Yield change (t/ha) of Valencia orange in response to changing temperature and CO2 concentration [Source: Rosenzweig et al. (1996)]

11. Analogue Scenarios Identification of recorded climate regimes which may resemble the future climate in a given region Assumption: climate will respond in the same way to a unit change in forcing despite its source and even if boundary conditions differ

12. Spatial Analogues Identify regions which today have a climate analogous to that anticipated in the study region in the future [Source: Parry & Carter, 1988] • Approach restricted by frequent lack of correspondence between other non-climatic features of the two regions • Causes of the analogue climate likely different from the causes of future climate change

13. Temporal Analogues Use climate information from a past time period as an analogue of possible future climate • Palaeoclimatic • Instrumental

14. Palaeoclimatic Analogues Use information from the geological record - fossils, sedimentary deposits - to reconstruct past climates • mid-Holocene, 5-6k BP, 1°C warmer • last (Eemian) interglacial, 125k BP, approx. 2°C warmer • Pliocene, 3-4m BP, 3-4°C warmer IPCC, 1990

15. Palaeoclimatic Analogues • changes in the past unlikely to have been caused by increased GHG concentrations • data and resolution generally insufficient, i.e., extremely unlikely to get daily resolution and individual site information • uncertainty about the quality of palaeoclimatic reconstructions • higher resolution (and most recent) data generally lie at the low end of the range of anticipated future climatic warming

16. Difference =0.4°C Instrumental Analogues Past periods of observed global- or hemispheric- scale warmth used as an analogue for the future Northern Hemisphere temperature record Lough et al., 1983

17. Instrumental Analogues The 1930s in the North American Great Plains have frequently been used as an analogue for the future. Mean temperature (°C) Precipitation (mm) Differences between 1931-1940 average and 1951-1980 average in the MINK states (Easterling et al., 1992)

18. Instrumental Analogues Palmer Drought Severity Index (PSDI) for the US Corn Belt, 1930-1980. [Source: Rosenberg et al., 1993]

19. Instrumental Analogues Rice-growing areas in Japan 0.4°C warmer than base Base, 1951-1980 Warm decade, 1921-1930

20. Instrumental Analogues ADVANTAGES • data available on a daily and local scale • scenario changes in climate actually observed and so are internally consistent and physically plausible • DISADVANTAGES • climate anomalies during the past century have been fairly minor cf. anticipated future changes • anomalies probably associated with naturally-occurring changes in atmospheric circulation rather than changes in GHG concentrations

21. Scenarios from GCMs GCMs are the “…only credible tools currently available for simulating the physical processes that determine global climate...”[IPCC] [Source: David Viner, UK Climate Impacts LINK Project]

22. What do GCMs do? Simulate the response of the global climate system to changes in atmospheric composition Growth in population, energy demand, changes in technology and land-use/cover Energy-economy models Greenhouse gas emissions Carbon cycle and other chemical models Atmospheric GHG concentrations Climate models Future climate projections

23. GCM evolution 1980s EQUILIBRIUM EXPERIMENTS late 1980s TRANSIENT EXPERIMENTS COLD START early 1990s WARM START

24. Warm start GCMs

25. CGCM1

26. Which GCM should I use? • Vintage • Resolution • Validity • Representativeness of results [Source: Smith and Hulme, 1998]

27. BUT ... • Climate models are not accurate • Different GCMs give different results • The future is uncertain - it is expensive to run many climate change experiments using different emissions scenarios • Climate model results are not at a fine enough spatial scale

28. Climate models are not accurate ...

29. Climate change integration t2 Global mean temperature (°C) t1 Time so we cannot use their output directly ... t1 is typically 1961-1990 t2 is a future time period, e.g., 2040-2069, representing the 2050s DT=t2-t1 Some models exhibit large inter-decadal variability, so average over 30 years to capture longer-term trend.

30. IPCC-TGCIA recommend 1961-1990 as the climatological baseline Role in climate scenario construction: • serves as a reference period from which estimated future change in climate is calculated • used to define the observed present-day climate with which climate change scenario information is usually combined

31. Specifying the Baseline Important for: • characterising the prevailing conditions under which an exposure unit functions and to which it must adapt • describing average conditions, spatial and temporal variability and anomalous events, some of which can cause significant impacts • calibrating and testing impact models across the current range of variability • identifying possible ongoing trends or cycles • specifying the reference situation with which to compare future changes

32. Sources of Uncertainty Cascade of uncertainty [Source: Hadley Centre for Climate Prediction and Research, UK Met. Office]

33. The future is uncertain ... IPCC Special Report on Emissions Scenarios (2000)

34. The future is uncertain ...

35. The future is uncertain ... 1.4-5.8°C

36. The future is uncertain ... 0.09-0.88m

37. SRES climate change

38. SRES climate change

39. Different GCMs give different results …

40. Different GCMs give different results …

41. Which scenarios? Cooler, wetter Warmer, wetter Cooler, drier Warmer, drier

42. Risk assessment approach • ADVANTAGES • makes (some) uncertainties explicit • good for risk assessment • can be applied at different scales • DISADVANTAGES • not yet a well developed methodology • requires a lot of model data to develop • expert assumptions still needed

43. Spatial Scale of Scenarios Effect of scenario resolution on impact outcome [Source: IPCC, WGI, Chapter 13]

44. Scenario Needs • What climate variables are essential for your study? • How many scenarios do you want? Which uncertainties are you going to explore? • Do you need local data for case studies/sites, or national/regional coverage? • What spatial resolution do you really need - 300km, 100km, 50km, 10km, 1km? Can you justify this choice? • Do you need changes in average climate, or in variability? • Do you need changes in daily weather, or just monthly totals?

45. Further Reading • IPCC TAR - Chapter 13 (www.ipcc.ch) • Smith & Hulme - Chapter 3: Handbook on Methods of Climate Change Impacts Assessment and Adaptation Strategies (http://130.37.129.100/english/o_o/instituten/IVM/research/climatechange/Handbook.htm) • Parry & Carter - Climate Impact and Adaptation Assessment. Earthscan, 166pp. • IPCC TGCIA Guidelines on Climate Scenarios (currently under revision)