Scientists find human fingerprints all over Australia's hottest year on record

http://www.theguardian.com/environment/planet-oz/2014/oct/03/scientists-find-human-fingerprints-all-over-australias-hottest-year-on-record

Australia had a hot one in 2013 – a real record breaker.

We started off with a heat wave that made January 2013 the hottest month on record that was part of the hottest summer on record that then became the hottest year on record.

Meteorologists and climatologists looking at records tend to express things by “anomalies” – how far above or below the long-term average is a particular temperature.

September 2013 had all the anomalous bells and whistles you could muster, managing to break above the long term average by 2.75C (4.95F) – a departure greater than any other month on record going back to 1910.

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Climate scientists Dr Sophie Lewis, of the Australian National University, and Professor David Karoly, of the University of Melbourne, ran two groups of computer models for a study into Australia’s scorching 2013.

In one group, they included the extra carbon dioxide in the atmosphere being added at the rates they are now. In another group of models, they left out the human contribution.

They found that on average, the computer models with current levels of carbon dioxide managed to reproduce the temperatures comparable to that scorching year of 2013 every six years.

For the computer models without the added greenhouse gas emissions, they got a year as hot as 2013 only once in more than 12,000 years.

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In the case of Australia’s record hot year, anthropogenic influences were a big contributor, to the point that the temperatures we experienced would have been virtually impossible without greenhouse gases. This doesn’t mean that natural variability isn’t important too.

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The study found that the risk of Australia getting a year of maximum temperatures hotter than 2002 is 23 times greater than it was in the late 19th century. There was an at least seven-fold increase in the risk of Australia getting a combination of extreme heat and drought occurring at the same time.

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