Climate Prediction on Timescales of Seasons to

Decades

A tool for sustainable development in the 21st Century

T N Palmer

ECMWF

Increasing levels of CO2 are changing the probability of

occurrence of spells of cold/warm wet/dry weather.

Multiple climate forecasts (varying uncertain initial conditions and

uncertain model parameters) can be used to estimate the impact of

increasing levels of CO2 on the probability of occurrence of

drought/flood/heatwave/cold snap.

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.

Probability of 1-in-20 year warm summer

Weisheimer and Palmer, 2005

Probability of 1-in-20 year dry summer

Probability of 1-in-20 year wet summer

Increasing Levels of CO2 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.

El-Niño

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.

Cumulative PDFs of standardised malaria incidence in Botswana five months in advance of the epidemic

-- high malaria years

-- low malaria years

ROC Score Precipitation Incidence

Event CMAP DEMETER CMAP DEMETER

Low1.00 (1.00-

1.00)0.95 (0.82-

1.00)1.00 (1.00-

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

Climatic linkage with meningitis in African Sahel

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.

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.

The LACES ProjectLarge Atmospheric Computation on the Earth Simulator

12-h development of Hurricane Earl: Sept.1, 1998: 1-km horizontal resolution

Conclusions• Increasing levels of CO2 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.