It was only in March of this year that the massive wildfires that began tearing through the national park in January near Australia’s capital city of Canberra were finally declared out. In the intervening weeks they consumed more than 80 percent of the park. This is just one example of the enormous toll taken recently by southeastern Australia’s unprecedented bushfires, which collectively killed more than 30 people, destroyed nearly 6,000 structures and wiped out hundreds of millions of animals.

The flames were fanned by a rare perfect storm of conditions, including strong winds, prolonged drought and searing temperatures—along with a boost from climate change. Global warming has pushed up the odds of such extreme fire events occurring in southeastern Australia by at least 30 percent—and likely by much more—according to a study submitted to Natural Hazards and Earth System Sciences. It is the most thorough analysis to date of the role of climate change in a particular wildfire event. The examination began as the blazes were still scorching forests and blanketing cities in smoke, impacting some of the researchers involved in the work.

The analysis suggests that although events of this magnitude will remain relatively rare in the future, firefighting efforts and other disaster-response systems need to prepare for rising odds, or they risk being overwhelmed. “I hope people will see this as the study that did show there is a link between climate change and the bushfires,” says co-author Geert Jan van Oldenborgh of the Royal Netherlands Meteorological Institute.

Climate scientists have increasingly been conducting what are called extreme event attribution studies to address the inevitable questions that crop up about the role of climate change in any number of weather extremes, from heat waves to floods. The World Weather Attribution consortium (WWA), a group of researchers who conducted the new research, has pioneered a way to do such analyses immediately after an event—rather than the months or years that early studies took to complete.

Wildfires are particularly tricky for such investigations because myriad factors drive them, including weather, fuel availability and ignition sources. Helping to set the stage for the recent fires were the facts that Australia had its hottest and driest year in 2019 and that large areas had been subject to drought for three years, along with highly conducive fire weather. The new WWA analysis considered the weather and climate aspects but not the ignition sources. The researchers examined trends in a risk measure called the Fire Weather Index, which includes factors such as precipitation, temperature, humidity and wind speed. They also looked at temperature and precipitation on their own, over an area of the states of New South Wales and Victoria between the Great Dividing Range mountain system and the coast.

When fires began igniting in the region during the Australian spring, 95 percent of the country had some of the highest fire index values on record, said WWA team member Sophie Lewis of the University of New South Wales during a recent press conference. There is only about a 3 percent chance of having such extreme values in any given year, the WWA researchers say. But according to their analysis, historical records show that such high fire indices are nearly four times more likely now than they were in 1900. Based on climate models that can compare worlds with and without anthropogenic warming, those indices are currently 30 percent more likely to occur than they were 120 years ago.

The team thinks the main climate driver behind the increased odds of exceptionally high fire indices is temperature. “The hot temperatures just pull the moisture out of the potential fuels,” such as trees, van Oldenborgh says. The historical records indicate the chances of the exceptional heat that gripped the region during the fires are 10 times higher now, compared with the beginning of the 20th century. But the climate models used in the study suggest such events are twice as likely because of climate change.

Van Oldenborgh says the results demonstrate that these models are consistently underestimating the rise in heat extremes with warming—something that the investigators also noticed when looking at heat waves in Europe and a trend they are now working to understand in an attempt to improve projections of future heat and fire risk.

Unlike the case with temperature, the team could not find a discernible trend in the extreme dryness that contributed to the ferocity and size of the fires. Previous research has shown this dryness was caused by La Niña and other natural climate swings, which are linked to ocean temperatures and influence atmospheric circulation. During this season, those phenomena happened to align in a way that made southeastern Australia weather ripe for encouraging fires.

Taken together, the study’s results show that although “natural variation was very important and will continue to be important in fueling these large fire seasons”—and although such events are likely to remain rare occurrences—climate change is making them “substantially more probable,” says John Abatzoglou, a climate scientist at the University of Idaho. He was not involved in the analysis but has investigated how climate change has influenced fire risk in the western U.S.

The new paper points to the need for governments and the disaster-response systems they have in place to take these rising risks into consideration, Abatzoglou says. He cites the example of Australia’s largely local and volunteer bushfire-fighting force, which was stretched thin during the recent blazes. Insurance companies are also paying attention to this research to better understand the changing risks, he adds.

The study’s authors hope that their work will help inform the reckoning over how to respond to climate change happening in Australia in the wake of the fires. “We do the best scientifically thorough study that we can do, and we hope this is input for the wider discussion,” van Oldenborgh says.