Title: Changes in temperature and precipitation annual extremes in the

IPCC AR4 multi-model ensemble

V.V. Kharin (1), F.W. Zwiers, X. Zhang, and G.C. Hegerl

1: Canadian Centre for Climate Modelling and Analysis,

Environment Canada,

Victoria, British Columbia, Canada

Abstract:

Temperature and precipitation extremes and their potential future

changes are evaluated in an ensemble of global coupled climate

models participating in the Intergovernmental Panel on Climate Change

(IPCC) diagnostic exercise for the Fourth Assessment Report (AR4).

Climate extremes are expressed in terms of 20-yr return values of

annual temperature extremes and 24-hr precipitation amounts.

The simulated changes are documented for years 2046-2065 and 2081-2100

relative to 1981-2000 in experiments with the SRES B1, A1B and A2

emission scenarios.

Overall, the climate models simulate present-day warm extremes

reasonably well on the global scale, as compared to estimates from

reanalyses. The model discrepancies in simulating cold extremes are

generally larger than those for warm extremes, especially in

sea-ice covered areas. Simulated present-day precipitation extremes are

plausible in the extratropics but uncertainties in extreme

precipitation in the tropics are very large, both in the models and

the available observationally based datasets.

Changes in warm extremes generally follow changes in the mean

summertime temperature. Cold extremes warm faster than warm extremes.

The excessive warming of cold extremes is generally confined to

regions where snow and sea-ice retreat with global warming. Relative

changes in the intensity of precipitation extremes generally exceed

relative changes in annual mean precipitation, particularly in

tropical and subtropical regions. Waiting times for late 20th century

extreme precipitation events are reduced almost everywhere. The very

large inter-model disagreements in the tropics reduce our confidence

in the projected changes in extreme precipitation.