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| A wildfire in New South Wales in February. Australia has been hit by brutal heat waves in the last two months. Credit NSW Rural Fire Service, via Associated Press |
"It was nothing short of awful," said Sarah Perkins-Kirkpatrick, of the Climate Change Research Center at the University of New South Wales, in Sydney. "In Australia, we're used to a little bit of heat. But this was at another level."
So Dr. Perkins-Kirkpatrick, who studies climate extremes, did what comes naturally: She looked to see whether there was a link between the heat and human-driven climate change.
Her analysis, conducted with a loose-knit group of researchers called World Weather Attribution, was made public on Thursday. Their conclusion was that climate change made maximum temperatures like those seen in January and February at least 10 times more likely than a century ago, before significant greenhouse gas emissions from human activity started warming the planet.
Looked at another way, that means that the kind of soaring temperatures expected to occur in New South Wales once every 500 years on average now may occur once every 50 years. What is more, the researchers found that if climate change continued unabated, such maximum temperatures may occur on average every five years.
For the overall 2016-17 summer in New South Wales, the researchers say, climate change made the hot average temperatures — which set records for the state — at least 50 times more likely than in the past.
The findings are the latest in what has become a growing field: studies that try to assess the influence of climate change on extreme weather as soon as possible. The idea is to offer scientific analyses of heat waves, floods and other events while people are still talking about them, and to counter the spread of misinformation, intentional or not, about the impact of global warming.
Climate scientists have long said that climate change should bring an increase in extreme events like dry spells and heat waves. Because warmth causes more evaporation and warmer air holds more moisture, climate change should also lead to more intense and frequent storms.
Studies have shown that these effects are occurring on a broad scale. But the natural variability of weather makes looking at individual events more difficult.
World Weather Attribution, which is coordinated by Climate Central, a research organization in Princeton, N.J., is one of a number of groups doing rapid analysis. Among other events, they have looked at flooding in Germany and France last May; high temperatures in the Arctic in November and December; and an usually strong storm that hit northern Britain in 2015.
Not all attribution studies have found a climate-change link. In general, studies of heat waves tend to produce the clearest signal of the influence, or not, of global warming.
Australian heat waves have been examined in the past, most recently in several studies that showed a clear link between climate change and a period of torrid weather in 2013. David Karoly, a scientist at the University of Melbourne, was involved in one of the studies, which took more than six months to produce.
"That was considered very rapid at the time," Dr. Karoly said.
As a member of World Weather Attribution, Dr. Karoly helped with the study of the recent heat waves, which took about two weeks.
A big difference between the two studies is in the use of computer climate models — both of the current atmosphere with its greenhouse gas emissions and of a hypothetical atmosphere as if those emissions had never occurred and climate change was not happening.
For the older study, as for most attribution studies in the recent past, the models were run over and over again, which took months. The newer, rapid studies use models that have already been run, extracting data as needed.
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