Residents look at the flames from a bushfire that erupted in Sydney’s western suburb of Castlereagh, New South Wales, on Sept. 10, 2013. (Saeed Khan/AFP/Getty Images)

Afterwards — after the blistering heat and the bushfires — they would call it the “Angry Summer.”

But whatever the description, the Australian summer of 2012-2013 provided a terrifying preview of a world under climate change. According to the country’s Bureau of Meteorology, a devastating heat wave in late 2012-early 2013 saw “records set in every State and Territory … the nationally averaged daily temperature rose to levels never previously observed, and did this for an extended period.”

What was truly astonishing is just how extreme the records were that summer — 44 different locations set all time high temperature records, including Sydney — and how long the heat lasted. “January 2013 brought record-setting heat to Australia; not just for days, but for weeks,” noted NASA.

The scorching temperatures at the start of 2013 then helped pave the way for a new national temperature record in 2013, surpassing the previous Australian heat record set just a few years earlier in 2005.

Here’s a NASA image of Australian temperature anomalies from Jan. 1-8, 2013:


Credit: NASA

And now, says a new report, it’s pretty hard to see how it could have all happened unless climate change was stacking the odds. The report, by the country’s independent Climate Council, finds that 2013, Australia’s record hottest year ever, was “virtually impossible” without climate change. And as for the 2012/2013 summer heat waves? Global warming made their frequency three times as likely, and doubled the chances that they’d reach the extreme heat intensity that they did.

The report was authored by Will Steffen, an adjunct professor who studies Earth system science at the Australian National University.*

So how can Steffen know how global warming changed the odds that the summer of 2012-2013’s “exceptionally large number of record high temperatures,” as he puts it, would occur?

The answer is that researchers have run many, many climate change models — high-powered simulations that use our understanding of the physics of the atmosphere and oceans — which can simulate temperatures with and without human-added climate factors. This allows them to compare just how often a given set of temperatures are expected to occur in the greenhouse enhanced world, versus a world in which somehow, we didn’t pump all that stuff up into the atmosphere.

This led to the following results:

* In a world without global warming, 2013’s record Australian temperature would only happen once out of every 12,300 years.

* The same approach suggests that global warming upped the odds of the Angry Summer’s heat waves by a factor of 3 or 2, depending on whether you’re referring to the frequency of heat waves or the magnitude of the heat waves themselves.

This week, Australia’s prime minister, Tony Abbott – who actually reversed the country’s carbon taxsurvived a leadership challenge from his own party.

* Correction: This post previously described Will Steffen as the director of the Climate Change Institute at the Australian National University. He left that post in 2012.