The context for the study is the record-smashing “Angry Summer” Australia just endured, which brought heat waves, brush fires, and both the hottest month and the hottest day the country has ever seen. According to the paper, by Sophie Lewis and David Karoly, the odds of such summers occurring have increased five fold between now and 2020 — and half the blame can be laid at the door of greenhouse gas emissions.
Climate always involves lots of natural variability, and Australia is no exception. The El Niño, a band of unusually warm water that cyclically develops across the Pacific Ocean, has historically been associated with unusually hot Australian summers. But the Pacific Ocean was recently almost in La Niña conditions — the opposite, colder extreme of the oscillation. That was the initial clue for Lewis and Karoly that connected the “Angry Summer” to human activity. As The Guardian reports:
“We cannot categorically ascribe the cause of a particular climate event to anthropogenic climate change; however, the roles of various factors contributing to the change in odds of an event occurring can be identified,” the two scientists write.
They examined the historical record of more than 150 years of observation, and found, repeatedly, that extreme summers tended to occur in step with El Niño years: in fact were three times more likely to happen in an El Niño year than a La Niña season.
Clearly, something else was at work in the Australian summer of 2013. Natural climatic variations were not likely to have caused the bush fires and the floods. It was possible to say, with more than 90 percent confidence, that human influences on the Australian atmosphere had dramatically increased the odds of extreme temperatures.
The key thing to understand when it comes to extreme weather is that the range of possible scenarios natural climate variations can produce exist along a bell curve. When human-driven global warming raises average temperatures, it shifts the bell curve so that more of the distribution lies in the extremes, increasing the odds of punishing heat, wildfires, floods, and all the rest in any given season.
Unfortunately, Australia is helping dig its own grave in some respects here. The country’s plans to double down on coal production and exports was noted by Greenpeace as one of 14 “carbon bombs” threatening the global climate. And all by themselves, the coal reserves Australia is considering exploiting could take up 75 percent of what the world can still burn without pushing global warming above two degrees Celsius. To top it off, Australia’s conservative opposition has vowed to undo the country’s embryonic carbon tax if it wins elections this September.
On the plus side, the price of Australian wind power is already outperforming that of fossil fuels — even in the absence of government assistance — with solar coming up rapidly behind it. And studies suggest that providing all of Australia’s electricity needs with renewables by 2030 is a goal that lies well within the realm of the realistically achievable.