Good news and bad on climate extremes

Extreme heat is of most concern (photo: Bob Beale)
Wednesday, 8 April, 2009
Bob Beale

The increases in temperature extremes Australia faces this century due to global climate change will not be quite as large as some have feared, according to a new study by UNSW researchers published in Geophysical Research Letters.

The team compared the climate models used by the Intergovernmental Panel on Climate Change (IPCC) and tested their accuracy against actual climate observations to select the strongest and weakest ones.

The researchers looked specifically at rare extreme events - those that occur on average once each 20 years - because heatwave conditions can dramatically affect biological, physical or human systems and are of most concern for planners and policy makers.

They found that the best-performing climate models simulated smaller rises in the temperature extremes compared with the models that performed poorly.

The study's authors caution that this is not good news: the increases in the extreme temperatures predicted by the strongest models are still extremely high and would generate heat waves much worse than the recent one that hit south-eastern Australia, they say.

The least accurate models were found to bias the average of all IPCC models towards higher temperature increases of about 3 to 5 degrees Celsius over most of the continent by the end of the century.  When those weak models were removed from the average, the predicted increase was 2 to 3 C (although in some regions the increase could be smaller or greater).

Recent heatwaves - such as the recent ones in Adelaide or Melbourne - have been "phenomenally hot", notes one of the authors of the study, Professor Andy Pitman, co-director of the UNSW Climate Change Research Centre.

Professor Pitman points out that Melbourne's record maximum temperature reached 46.4 C during the heatwave and power systems failed and trains were stopped by warped rails. At Hopetoun Airport in Victoria, a new record maximum temperature for the State was recorded on 7 February at 48.8 C.

"Even with our revised projections, adding two or three degrees to 47 C days is not a prospect I think anyone would like to experience," he says. "The lower figures are not as bad as 3 to 5 C, but they're still very bad and emphasise the need to aggressively cut greenhouse gases on a global scale.

"While we have not determined if this result is common to other continents, our results were similar over temperate, sub-tropical and tropical regions so we think its likely that our results can likely be extrapolated elsewhere."

The study was authored by Sarah Perkins, Professor Pitman - both of the UNSW Climate Change Research Centre- and Dr Scott Sisson, UNSW School of Mathematics and Statistics.

Media contacts:

Professor Andy Pitman:

Dr Scott Sisson:

UNSW Faculty of Science media liaison: Bob Beale 0411 705 435