Global warming played a big role in generating long-lasting heat waves that fueled Australia's deadly 2019-2020 wildfire season, a new study by an international team of scientists has concluded.
Human-caused warming increased the chances by at least 30 percent for the extreme fire weather that dried out soil, grass, brush and trees, the research found. The heat buildup caused by greenhouse gases probably played an even bigger role than the researchers were able to demonstrate, said University of Oxford climate scientist Friederike Otto, one of the authors of the new study, released Wednesday.
"We found that it was at least 30 percent, but it's likely much higher because the models underestimate extreme heat trends, one of the very important parts of the equation," Otto said.
In context with World Weather Attribution's other recent studies, the big takeaway for Otto is the renewed finding of how global warming is driving heat waves, which contribute to other extremes like droughts and fires.
"That is a real game-changer in most parts of the world and it's quite different from most other impacts," she said. "Climate change makes the weather completely different. We need to get better at predicting heat waves so we can prepare better. Many parts of the world don't even record heat waves, so there is a lack of awareness that these events are happening."
A 2017 study showed that heat waves are approaching deadly thresholds for millions of people, including thousands in U.S. cities. The extremes have continued in the last few months, with Eurasia baking in a record-warm winter and the average winter temperature in Moscow surging to above 0 degrees Celsius (32 degrees Fahrenheit) for the first time since record keeping began more than 200 years ago. There were record highs on the Antarctic Peninsula and a record-dry and warm February across large parts of California.
World Weather Attribution includes scientists from Holland, France, Australia, the U.K. and the U.S., as well as experts with the Red Cross Red Crescent Climate Centre. The study has been submitted for peer review by other scientists. Identifying the global warming fingerprint on extreme storms, heatwaves, cold spells, and droughts helps communities prepare, the scientists said.
The fires rekindled public debate about Australia's climate and energy policies, with some media and politicians denying the role of fossil fuel emissions in the growing global climate crisis and downplaying the seriousness of the fires. The new report shows scientifically that global warming has already increased the wildfire risks to communities in Australia.
Wildfires burned in Australia from November 2019 through February 2020 across about 73,000 square miles, an area nearly as big as Nebraska, killing at least 34 people and an estimated 1.5 billion animals. The fires, some sparked by lightning, others by arson, also sent choking smoke wafting across major cities in eastern Australia for weeks on end.
Some of the smoke even reached parts of Antarctica and darkened the snow and ice on New Zealand glaciers. The fires also spewed about 900 million tons of carbon dioxide into the atmosphere, about double Australia's annual fossil fuel emissions, other scientists estimated.
Australian climate scientist Sophie Lewis, another of the study's authors, said the fires disrupted the daily lives of millions of people.
"I live in southeastern Australia. We spent weeks inside our home to try and avoid the hazardous smoke," she said. "Events prior to the current summer were extreme, with new records set for high wildfire danger, and the bushfire season started months early. These are unprecedented events with huge costs. That's why it's important to explore them from a scientific standpoint."
Thousands of people in southeastern Australia were evacuated and about 83 percent of a national park in the region was burned. The summer of 2019-2020 ended up as the second-warmest on record in Australia, ranking just behind the previous summer, she added.
A Global Warming Fingerprint
In the new study, the scientists analyzed weekly, monthly and seasonal fire-weather measurements across the areas that burned most intensely, between the Great Dividing Range and the sea in New South Wales and Victoria.
The findings include a sharp increase in the risk of fire weather since 1979. More long-term, the overall probability for dangerous fire conditions has increased more than four times since 1900. The chances of high fire danger in any one month have increased ninefold, the study found, and if the average global temperature increase reaches 2 degrees Celsius (3.6 degrees Fahrenheit), fire weather like this past summer would be at least four times more likely, compared to 1900. The researchers also found that:
Global warming has increased the warmth of heat waves by 1 to 2 degrees Celsius (1.8 to 3.6 degrees Fahrenheit) since 1900.
A heatwave of this intensity is at least 10 times more likely now than it would have been around 1900.
The observed trend of extreme weather is outpacing the trends predicted by climate models.
There is no attributable trend in Australia toward extremes of dry weather like the ones observed in 2019.
The extreme fire weather conditions of 2019-2020 were intensified by record-setting shifts in regional weather patterns.
There is evidence that human-caused climate change is also increasing the fire risk in ways that the attribution study didn't capture, said Nerilie Abram, a climate extremes researcher with Australian National University and the Australian Centre of Excellence for Climate Extremes.
Research suggests that global warming is intensifying the Indian Ocean Dipole, an oscillation in sea surface temperatures similar to the Pacific's El Niño, which increases fire risk in southeastern Australia. Human-caused warming is also shifting winter rainstorm tracks away from southwest and southeast Australia, said Abram, who was not involved in the new study.
"A clear cool-season drying trend has been evident in southwest Australia since the 1970s," she said.
She said the study could have been more complete, with additional input from Australian experts who understand important regional climate and fire processes, including long-term drought, which is "preconditioning the forests here to burn."
What are the Limits?
Climate models project a relatively gradual increase in heat, "but extremes are increasing much faster," said van Aalst, who was also part of the World Weather Attribution group that studied the links between global warming and the Australian fires.
"What is happening with that heat is really a challenge around the world," he said. "It's a warning sign that we're reaching the limits of what we can cope with."
Just in the last year, van Aalst said, extreme heat waves around the world probably killed thousands of people, deaths that are only now showing up in annual morbidity statistics. And the fires in Australia stretched emergency services to their limits, with "stress on fire brigades that were deployed for 100 days," he said.
The new study will help plan for a future that holds more extremes because of global warming, said Cam Walker, a volunteer firefighter and Friends of the Earth conservation activist in Australia.
"Those of us on the frontlines are facing changed conditions, especially longer and more intense fire seasons, and we know that fire fighting strategies need to evolve. However, it is hard to cut through the opinionated noise that crowds out sensible discussion in the public realm," Walker said, adding that after the fires, conservative media outlets and climate deniers blamed them on a lack of preventive measures.
We've been Warned
Penn State climate researcher Michael Mann, who was on sabbatical in Australia during the fires, said that Australian scientists explicitly warned about the growing wildfire danger as early as 2008 in a climate report.
"They concluded that the bushfire season would 'start earlier, end slightly later and generally be more intense' and that 'this effect increases over time, but should be directly observable by 2020,'" he said.
Mann said one of the most important points of the new study is the renewed finding that current heat extremes are far beyond what models have projected. A similar study last summer on the summer heatwave in Europe reached a similar conclusion, and also found that European heat extremes would have been all but impossible without global warming.
University of New Mexico climate and fire researcher Matthew Hurteau said the study aligns with similar research in the West, showing that human-caused climate change is responsible for about half of the area burned since the mid-1980s.
"As the temperature goes up, the fuels dry out because a warmer atmosphere can hold more water than a cooler atmosphere," he said. "The western U.S. can expect increasing areas burned with additional warming."