Uncertainty, climate scenarios and adaptation Suraje Dessai Tyndall Centre for Climate Change Research, UK and School of Environmental Sciences University of East Anglia, Norwich, UK CLIMATE CHANGE KIOSK EVENT CALENDAR GLOBAL CLIMATE SCIENCE

Uncertainty in climate change IMPACTS [Source: Carter, 2000]

Why might we need probabilities of climate change? To assess the seriousness of impacts we need to know how likely they are to occur (Schneider, 2001, 2002). Probabilities represent uncertainty explicitly and thus better fit a risk assessment framework: “the reason for quantifying risk it to make coherent risk management decisions under uncertainties and within resource constrains” (Pate-Cornell 1996); this allows decision- makers to hedge the risk of climate change Several communities (water resource managers and engineers) demand it! The central role played by prediction in guiding decision-making.

What are the problems in estimating probabilities? Probabilities only one method to represent uncertainties Confusion about probabilities, risk and uncertainty (various definitions and typologies) Stirling (1998) Incomplete vs unknowable knowledge Epistemic vs stochastic uncertainty Subjective vs aleatory uncertainty Type B vs type A uncertainty Reducible vs irreducible uncertainty …

Different types of uncertainty in the context of climate change Type of knowledgeType of uncertainty Possible to represent with probabilities IncompleteEpistemicYes, but limited by knowledge Incomplete- Unknowable Natural stochasticYes, but with limits UnknowableHuman reflexiveNo, scenarios required

Emission scenarios Global climate sensitivity Regional climate change Local climate change

Sensitivity of adaptation decision-making Probability Climate variable A B C D E F G Decisions Adaptation decisions A – Alternative supply required B – Build new storage C – Operations management changes D – No changes required E – Operations management changes F – Develop small infrastructure G – Develop big infrastructure

Sensitivity of adaptation decision-making Probability Climate variable A B C D E F G Decisions Adaptation decisions A – Alternative supply required B – Build new storage C – Operations management changes D – No changes required E – Operations management changes F – Develop small infrastructure G – Develop big infrastructure

Further reading Dessai and Hulme (2003) Does climate policy need probabilities? Tyndall Working Paper 34 g_papers/wp34.pdf