Conservation comment: The climate change answers

NEW SCIENCE: A new branch of climate science is starting to provide answers to the question of whether a specific storm (or heatwave or drought) was at least partly attributable to climate change.PHOTO/FILE

CLIMATE scientists have been cautious about attributing specific weather events to global warming. Because weather is variable, it's impossible to know whether climate change caused any particular drought or flood. So scientists have steered away from making firm connections.

Until now. A new branch of climate science is starting to provide answers to the question: was this drought (or heatwave or storm) at least partly attributable to climate change? In some cases, the answer seems to be a cautious yes. Although it is not possible to say categorically that climate change has caused any individual weather event, scientific attribution does not require certainty. It deals in probabilities. Even now, doctors cannot be sure that a case of lung cancer has been caused by smoking - the patient might have got the disease anyway.

The science of weather attribution started in 2003 with an article in Nature, "Liability for climate change" by Myles Allen of Oxford University. It showed that human contributions to climate change can be calculated by looking at what the climate would have been like if people had not increased greenhouse gas emissions.

That meant comparing observations of the weather with computer models of what might have happened without climate change. Much climate science depends on such models, which describe the complexities of the climate. By running them using different assumptions (for example, no increase in greenhouse gas emissions, or more volcanic activity), and comparing the results with reality, it is possible to reveal the probable effects of the emissions. With lung cancer it is possible to compare groups of smokers and non-smokers; with climate change computers have to simulate the equivalent of the non-smokers.

The strongest evidence for human influence can be seen in heatwaves, such as Australia's "angry summer" of 2013, its hottest on record. In a study in Geophysical Research Letters, David Karoly of the University of Melbourne argues that it is possible to say with considerable confidence that human influence increased the risk of such high temperatures fivefold, at least. This heatwave, he argues, would have been "virtually impossible" without climate change.

Nine studies of heatwaves in Europe, China, Japan and Korea were undertaken in 2013. All showed that man-made climate change had increased the likelihood of exceptional heat. In Korea daily minimum summer temperatures were 2.2C above the 1971-2000 average. The study found that climate change had boosted the chance of this happening tenfold.

Germany is likely to have a summer as hot as that of 2013 about once in seven years now. Before industrialisation the odds were one in 80. For Europe, the odds rose by 35 times - the result of changes to ocean currents and the great Arctic melt, and to emissions of greenhouse gases and aerosols. You would expect more heatwaves with more global warming. But climate change also seems to be contributing to droughts, though the evidence here is weaker.

All these findings emphasise the problem; this is science. It is rarely absolute, frequently confusing and sometimes counter-intuitive. But it is the only way to establish the answers to the questions and problems that confront us. This new science is a welcome development for climatologists.

-Ian Sutherland is a retired pathologist who has lived and worked in many predominantly warm, countries and has always had an interest in conservation and environmental matters