Human activity linked to hottest summer on record

Tom Arup Environment editor

The Age, June 27, 2013 

Australia's record-breaking heat last summer was at least five times more likely to have occurred in a world subject to to greenhouse gas emissions from human activities than one without, a study has found.

University of Melbourne researchers drew the conclusion after examining 90 model simulations and climate observations from summers of the past 100 years.

They used nine climate models — those used by the United Nation's Intergovernmental Panel on Climate Change — to test how likely the record temperatures in Australia between December and February would be in a world with and without human-induced global warming.

They found it was very likely — with 90 per cent confidence — that summers such as that of 2012-13 were at least five times more likely to occur due to man-made climate change than in a world facing only natural variation.

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The researchers also found the frequency of extremely hot summers would continue to increase due to global warming.

"These results support a clear conclusion that anthropogenic climate change had a substantial influence on the extreme summer heat over Australia and that natural climate variations alone are unlikely to explain the recent record summer temperature," the researchers say in a paper published in the journal Geophysical Research Letters.

The Bureau of Meteorology says temperatures throughout the country last summer were 1.11 degrees above the long-term average, making it the hottest since records began.

The average temperature has risen 0.9 degrees since 1910 — an increase scientists have linked to rising greenhouse gas concentrations in the atmosphere.

Study co-author David Karoly said this year's hot summer was "at least five times more likely to have happened in a world with increasing greenhouse gases than in a world with natural variability".

"That is already a substantial change, and we are talking about climate change which is only less than one degree so far globally, ramping up to four or five degrees towards the end of that century," Professor Karoly said.