National climate scenarios

1. National climate scenarios Suraje Dessai Sustainability Research Institute and ESRC Centre for Climate Change Economics and Policy, School of Earth and Environment, University of Leeds, UK Climate Change Impacts, Adaptation and Mitigation (CC-IAM) Research Group, Faculty of Sciences, University of Lisbon, Portugal

2. Outline • Rationale for climate scenario construction • The UK experience of national climate scenarios • Re-thinking national climate scenarios workshop

3. Scenario and climate scenarios • 1950s – usage in military strategy and planning • 1970s – usage in the energy business (Royal Dutch/Shell; Van der Heijden, 1997). • 1980 – first climate scenario (Wigley et al. 1980)

5. Scenarios and climate scenarios • 1950s – usage in military strategy and planning • 1970s – usage in the energy business (Royal Dutch/Shell; Van der Heijden, 1997). • 1980 – first climate scenario paper (Wigley et al. 1980) • 1980s-90s – scientific papers and policy documents use and develop climate scenarios • 1990s – first national climate scenarios published (UK) • 2001 – IPCC TAR WG1 devotes a chapter to the science of climate scenario construction (Mearns et al., 2001) • 2009 – first probabilistic climate change projections published (UK)

6. Climate scenario definition • A plausible and often simplified representation of the future climate, based on an internally consistent set of climatological relationships that has been constructed for explicit use in investigating the potential consequences of anthropogenic climate change, often serving as input to impact models. Climate projections often serve as the raw material for constructing climate scenarios, but climate scenarios usually require additional information such as the observed current climate. A climate change scenario is the difference between a climate scenario and the current climate (IPCC AR5 WG1)

7. Climate scenarios • Types: synthetic (arbitrary), analogues (temporal and spatial), model based (GCMs, RCMs, statistical, etc.) and hybrids.

8. Climate ‘relocation’ ofEuropeancities CNRM ARPEGE-Climat model Hadley Centre HadRM3H model 2080s under SRES A2 scenario Hallegatte et al.(2007) Using climate analogues for assessing climate change economic impacts in urban areas. Climatic Change 82:47–60

10. National climate scenarios • Climate scenarios are negotiated amongst various actors (Hulme and Dessai, 2008) • Multiple functions: pedagogic, motivational or practical • Often endowed with governmental authority to inform decision-making • Increasingly used to inform adaptation decisions

11. A chronology of UK climate scenarios Climate change act UKCP09 projections 2009 COP-15 fails to agree a post 2012 regime

12. A chronology of UK climate scenarios UKCIP98 UKCIP02 CCIRG91 CCIRG96 UKCP09

13. UK climate scenarios (Hulme and Dessai, 2008)

14. Chronology of estimates of summer precipitation change (%) for the southeast of England

15. UKCIP02

16. UKCP09 projections • First projections designed to treat uncertainties explicitly (Murphy et al. 2009) • More informative but also more complex than previous scenarios (Murphy et al. 2009) • Designed to inform adaptation decisions • Cost £11 million • User Interface • Reviewed by Steering and User group and 5 experts

17. From UKCIP02 to UKCP09

18. UKCP09: sampled uncertainties

19. UKCP09

20. UKCP09 uncertainties • Modelling uncertainty – arising from incomplete understanding of the climate system, and our inability to model it perfectly (PPE: model parameters, the sulphur and carbon cycles) • Natural climate variability – arising from both internal and external factors on the climate system • Emissions uncertainty – arising from not knowing the amount of future global greenhouse gas emissions • Contributions to uncertainty from downscaling

21. UKCP09 map

23. Contributions to the uncertainty in winter precipitation changes for 2070-2099 relative to 1961-1990, at selected 25 km grid squares.

24. Figure 4.4: 10, 50 and 90% probability levels of changes to the average daily mean temperature (ºC) of the winter (upper) and summer (lower) by the 2080s, under Medium emissions scenario.

25. Figure 4.10: Changes in annual (top), winter (middle) and summer (bottom) mean precipitation (%) at the 10, 50 and 90% probability levels, for the 2080s under the Medium emissions scenario.

26. The greatest difference between UKCIP02 and UKCP09

27. Demand for climate scenarios • Early mainstreaming into planning (e.g., water resources in late 1990s) now more diverse • Success of UKCIP (1997-) • Research demand (e.g., ARCC programme, 2007-17) • Climate Change Act (2008) • Adaptation Reporting Power (2009): “The UKCP09 Projections are likely to be a useful tool for some organisations in undertaking assessments of their risks from climate change. They will allow decision makers to consider a range of possible future climates, as well as an estimate of the uncertainties surrounding those changes.” (Defra, 2009, p. 8). • Climate change risk assessment (2012)

28. Prevalence of UK national climate scenarios in the academic literature Number of peer-reviews papers that include a UK national climate scenario in the topic (includes title, abstract and keywords). Searched in Scopus (24 July 2014).

29. (Re)Thinking National Climate Scenarios Workshop – Dec 2013 • Some research on the construction of UK climate scenarios (Hulme & Dessai, 2008) and its use (Tang & Dessai, 2012) but much remains unclear or undocumented • An international comparison has never been done (to my knowledge) • Aims and objectives of the workshop: • Reflect on the process of national climate scenario construction • Understand what lessons can be learnt about the social, political and technical issues that shaped the construction of national climate scenarios • Think and discuss the next generation of national climate scenarios

30. A chronology of selected national climate scenarios

31. National climate projections in Europe Slide by Stefan Fronzek: adopted from Füssel(2014), in Capela et al. (eds.) Adapting to an Uncertain Climate – Lessons from Practice

32. Some reflections • Tension: “Keep the methodology understandable” vs“Take full advantage of new science and tools” • Separate development and delivery as far as possible (publishing methodology/external review) • Plan strategically for product support and development (It’s a Climate Service) • Keep the rigour on uncertainties, but provide a more flexible set of storylines as a front-line product • Tension: Balance user needs against what science can credibly provide • Keep things simple: unless additional complexity adds value • Fitness-for-purpose • “credibility”: are the scenarios plausible, authoritative and consistent? • “relevance”: do the scenarios fulfill the user needs? • “legitimacy”: are the scenarios constructed in a transparent way? • XXXX does not (yet) provide actionable climate information

33. Treatment of uncertainty • Variety of approaches: PPE, MME, statistical emulators, scenarios • Relevant Dominant Uncertainty (RDU): is the source of uncertainty or error that is the primary limit on the fidelity of our probability forecasts • Communicating Immature Probability forecasts will carry less risk to the credibility all science-based decision support when the RDU is discussed and your Probability of a Big Surprise is provided, explicitly. Why communicate an immature PDF at all? (Lenny Smith) • Volunteer computing: almost limitless computer power (weather@home) • Hierarchy of approaches needed, but connected

34. Use of scenarios/projections in decision-making • Various UK examples of use: water resources planning, Climate Change Risk Assessment (CCRA), energy, etc. • User: “we need national climate scenarios less than we think we do”; vulnerability-led approach.

35. Where Are We Headed? • Generic scenarios are inherently limited – shouldn’t expect too much – modesty/humility • Focus more on process and insight rather than model and predictions • National Centre for Climate Services – tailoring; where is the boundary between public and private? • Early days for decadal predictions (experimental – need to be skilful and reliable) • Define a climate science agenda that begins with national vulnerabilities (narrative will help) • Are PDFs inherently dangerous?

36. Extras

37. Answers to the questions by one participant • What kind of uncertainty can or should be quantified? • Identify what uncertainty becomes important at what scales but • Internal variability, structural, parameter, inadequacy, predictability, implementation • Does the representation of uncertainty in climate models encounter unique epistemic/technical challenges? • Not unique, potentially most important • Epistemic – need to increase awareness that this is unavoidable (does Gödel’s incompleteness theorem apply here?) • Technical – no, but just about the hugest out there

38. Answers to the questions by one participant • What are the limits to modelling uncertainty? • Can’t do anything about models being wrong • More important are the technical limits • But may not need “the works” depending on application • Data! • Were (are?) simpler approaches possible? • Identify the plausible & the potentially important • Refuse to be precise / design to fail? • Is consistency across scenarios needed? • Some would help • More important is compatibility and comparability