1. Climate Prediction on Timescales of Seasons to Decades A tool for sustainable development in the 21 st Century T N Palmer ECMWF

8. Increasing levels of CO 2 are changing the probability of occurrence of spells of cold/warm wet/dry weather.

10. Multiple climate forecasts (varying uncertain initial conditions and uncertain model parameters) can be used to estimate the impact of increasing levels of CO 2 on the probability of occurrence of drought/flood/heatwave/cold snap.

11. Ensemble Climate Forecasting An ensemble is a set of predictions, each member with slightly different initial conditions and using slightly different model approximations. Ensemble gives - most likely prediction - estimate of uncertainty - probability of occurrence of extreme climatic conditions.

12. Probability of 1-in-20 year warm summer Weisheimer and Palmer, 2005

13. Probability of 1-in-20 year dry summer

14. Probability of 1-in-20 year wet summer

15. Increasing Levels of CO 2 are Predicted to Change the Risk of Extreme Seasonal Climate Anomalies. As part of an overall adaptation strategy to lessen the impact of inevitable climate change, particularly in developing countries, the use of climate models to predict risk of particular occurrences of seasonal climatic extremes months to seasons ahead, will be of increasing importance.

16. El-Niño

17. Thomson, M.C., Doblas-Reyes, F.J., Mason S.J., Hagedorn, R., Connor S.J., Phindela, T., Morse, A.P. and Palmer, T.N. Malaria early warnings based on seasonal climate forecasts from multi- model ensembles. Nature, 439,576-579.

18. Cumulative PDFs of standardised malaria incidence in Botswana five months in advance of the epidemic -- high malaria years -- low malaria years ROC ScorePrecipitationIncidence EventCMAPDEMETERCMAPDEMETER Low1.00 (1.00-1.00) 0.95 (0.82- 1.00) 1.00 (1.00- 1.00) High1.00 (1.00-1.00) 0.52 (0.25- 0.78) 0.94 (0.80- 1.00) 0.84 (0.65- 0.98) Low malaria incidence High malaria incidence

19. Climatic linkage with meningitis in African Sahel

20. Webster P.J., Anderson, D.L.T. Chang, H.- R., Grossman, R., Hoyas, C., Hopson, T., Shami, K., Subbiah, A. and Palmer, T.N. Regional application of monsoon dynamics: implementation of a three-tier flood and precipitation forecasting scheme for Bangladesh and surrounding regions. CLIVAR Exchanges, 9, 21-25.

21. Challinor, A.J., Singo, J.M., Wheeler, T.R. and Doblas-Reyes, F.J., 2005. Probabilistic simulations of crop yield over western India using the DEMETER seaonal hindcast ensembles. Tellus 57A, 498-512.

22. The LACES Project Large Atmospheric Computation on the Earth Simulator 12-h development of Hurricane Earl: Sept.1, 1998: 1-km horizontal resolution

23. Conclusions Increasing levels of CO 2 are gradually changing the probability of occurrence of extremes of weather. Ensemble forecast techniques give probabilistic estimates of climate change. The same techniques and models can be used to make seasonal climate forecasts - a increasingly valuable tool to help society, especially in developing countries, adapt to the changing risk of climate extremes. The accuracy of climate forecasts is compromised by inadequate computational resources.