Lethal Heating: 03/09/20

09/03/2020

(AU) Climate Change Made Australia's Devastating Bushfires More Likely, Scientists Confirm

TIME - Amy Gunia

Human-caused climate change made the bushfires that ravaged Australia during the most recent fire season more likely, according to a study published Wednesday.
Researchers at the World Weather Attribution consortium say that climate change increased the risk of the weather conditions that drove the fires by at least 30%.
The full influence of climate change was likely even greater, the study says, since models tend to underestimate trends in extreme heat.
The coalition of scientists from around the world looked at bushfire conditions in southeastern Australia using a measurement called the Fire Weather Index, which takes into account temperature, humidity, rainfall and wind to determine fire risk.
The group also analyzed extreme temperatures and drought, and found that human activity doubled the chances of heatwaves. They did not find significant trends related to drought conditions.
The study “nails down the linkage of the bushfires to climate change,” says David Bowman, director of the Fire Centre Research Hub at the University of Tasmania, who was not involved in the analysis.
“Probably the study is conservative,” he tells TIME via email.
Bushfires are an annual occurrence in Australia, but the most recent fire season, which was intensified by drought conditions and unprecedented heat, was one of the worst in the country’s history. Last year was the hottest and driest on record in Australia, according to a report released in January by the country’s Bureau of Meteorology.
The fires, which ripped across large parts of the country in 2019 and early 2020, scorched more than 44 million acres and killed more than two dozen people. Over a billion animals may have died in the blaze, according to an estimate by an ecologist at the University of Sydney.
The bushfire crisis reignited debate over climate change in the country, with some Australians calling for their government to take a tougher stance on the issue.
Australian Prime Minister Scott Morrison has acknowledged that climate change may be impacting the bushfires, but he has rejected the link between his country’s emissions and the fires.
“To suggest that with just 1.3% of global emissions, that Australia doing something differently, more or less, would have changed the fire outcome this season…I don’t think that stands up to any credible scientific evidence at all,” he said in a radio interview with the Australian Broadcasting Corporation.

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(AU) Climate Change Affected Australia’s Wildfires, Scientists Confirm

New York Times - Henry Fountain

The Dunn Road fire burned in southeastern Australia in January. Credit...Sam Mooy/Getty Images

Confirming what had been widely suspected, researchers have found that human-caused climate change had an impact on Australia’s recent devastating wildfires, making the extremely high-risk conditions that led to widespread burning at least 30 percent more likely than in a world without global warming.The researchers said the full influence of climate change on the fires was probably much greater, but that climate simulations, which form the basis of this type of study, underestimate trends in extreme heat in Australia compared with real-world observational data.

“We’re very sure that is a definite number we can scientifically defend,” said the lead author of the study, Geert Jan van Oldenborgh of the Royal Netherlands Meteorological Institute, referring to the 30 percent figure.
But the real influence of climate change on the recent fire season in Australia is greater, he added. “We think it is much larger than that, but we can’t prove that until we find out why there is this discrepancy between the observations and the climate models.”
The research is the latest in a growing subfield of climate science: attribution studies that look for links, or the lack of them, between climate change and specific weather-related events, often within weeks of an event. The studies usually compare models of current conditions to those of the world around 1900, before large-scale emissions of carbon dioxide and other planet-warming gases began.The Australian study was conducted, like many others, by an international group of scientists called World Weather Attribution. It was made public on Wednesday before being peer reviewed and published in a scientific journal, but scientists with the group said it followed what are now well-established practices for such studies.
Record warmth and dryness last year led to a severe wildfire outbreak in Australia, with an estimated 50 million acres burned, including more than 16 million acres in the southeastern part of the country, which was most affected. All told, at least 34 people were killed and nearly 6,000 homes and other structures were destroyed.
Dr. van Oldenborgh said the study was the most complicated the group had ever conducted because wildfires are a complex phenomenon affected not only by heat and precipitation but also by wind, humidity and other factors.
The researchers looked at the influence of climate change using a measurement standard called the Fire Weather Index, which takes all those factors into account to determine the risk of wildfire in a specific area at a specific time. They calculated the index values across southeastern Australia during the peak burning period of December and January.
Those values were extremely high, and were 30 percent more likely to be that high now than before 1900. Put another way, the researchers said, such high values are about four times more likely now than they were before.
The study also separately analyzed the influence of climate change on the extreme heat that Australia experienced during the fire season, and on the lack of rainfall during the same period. It found that extremely hot weeks like the fourth week of December, the country’s hottest on record, were at least twice as likely now than before 1900. The analysis of lack of rainfall found no significant trend related to climate change.
Benjamin M. Sanderson, a researcher at the European Center for Research and Advanced Training in Scientific Computing in Toulouse, France, who was not involved in the study, said the findings were reasonable.
“You can quite solidly say that extreme high temperatures play a role in fire risk,” he said. “And anthropogenic influences are easily detectable in terms of extreme temperatures.”
But he agreed with the researchers that wildfire is complex, and said the Australian disaster exposed the weaknesses of today’s climate models: they have difficulty drawing the connections between climate and fire.
“There are some events on the ground that have huge human and ecological impacts,” he said. “This was one of them. You look at what came out of the models and realize they were not very good at representing the severity of this process.”
Dr. Sanderson, together with a colleague, Rosie A. Fisher, wrote a commentary in Nature last month arguing that improvements in modeling are needed to better capture the severity of wildfires as they evolve in a changing climate.
“This is really a case where the real world is beginning to throw events at us before science is realized,” he added. “Which is a scary place to be.”

Credit...Pamela Schramm, via Reuters

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(AU) Climate Change Made Australia’s Devastating Fire Season 30% More Likely

Nature - Nicky Phillips

A fire engine surrounded by bush-fire smoke in February near the town of Bumbalong, south of Canberra, Australia. Credit: Peter Parks/AFP/Getty

The extreme fires that razed more than 18 million hectares of bush in Australia late last year were significantly more likely because of human-induced climate change, say an international group of climate scientists who have analysed the disaster.
The researchers’ results, released today, suggest that human-induced climate change increased the risk of the weather conditions that drove the fires by at least 30%.
Australia experiences bush fires almost every summer, but the latest event was unprecedented in its severity and scale. The World Weather Attribution (WWA) project sought to measure global warming’s contribution to the dangerous bush-fire conditions experienced in southeast Australia over several months. Fires in the region were particularly severe, and killed dozens of people and destroyed thousands of homes.
“This is a highly conservative assessment,” says David Karoly, a climate scientist based in Melbourne at the Commonwealth Scientific and Industrial Research Organisation who was not involved in the analysis.

Future concerns
The group assessed bush-fire conditions with a index that tracks ‘fire weather’. This calculates the chance of fire in a location based on variables such as temperature, humidity, wind and rainfall. The analysis did not consider non-weather factors, such as how a fire started.
The researchers also say the result is conservative. Models have mostly underestimated the rise in temperatures that has been observed since the Industrial Revolution, says Geert Jan van Oldenborgh, a climate researcher at the Royal Netherlands Meteorological Institute in De Bilt, the Netherlands, and co-author of the WWA analysis.
Even accounting for model uncertainties, Karoly says that the fire conditions experienced in Australia this summer are a baseline for what is possible in the world’s current climate, which has warmed by around 1ºC compared with pre-industrial levels. But conditions are going to get a lot worse as the planet warms by another degree or two, as is expected, he says.
The team also examined whether climate change influenced two of the components that are used to measure fire-weather: extreme temperatures and drought. The results, which have not been peer reviewed, suggest that while human activity doubled the chance of heatwave conditions during the fires, the models did not show that climate change contributed to the extremely dry conditions that Australia experienced.

Observed trend
In a second analysis that used real-world observations, rather than models, the WWA project looked at changes in observed fire risk since 1979. The researchers found that the likelihood of the extreme fire risk experienced in 2019–20 has increased fourfold — and possibly by more than ninefold — between 1900 and today. The reason that the observed trend is higher than the modelled trend is because factors other than climate change, such as changes in land use, might have also contributed to increased fire risk, say the authors.
Climate change definitely played a part in the catastrophic fires, says Andy Pittman, a climate scientist at the University of New South Wales in Sydney. But he questions whether the modelling results are accurate and meaningful given that models have a limited ability to simulate fire events. For instance, models can’t simulate the drought that much of Australia has experienced over the past two and a half years or the huge amount of fuel that fed the fires — probably two major influencing factors of the event, says Pittman.
“I’ve used climate models for 30 years and I think they are hugely valuable, but this sort of study uses them in ways that I think are beyond their capability,” he says. He also thinks that fire indices, such as the fire-weather index, overemphasize temperature’s effect on fire-weather.
Friederike Otto, a climate modeller at the University of Oxford, UK, and a co-author of the WWA analysis, acknowledges that models struggle to simulate temperature extremes or droughts at a regional and local scale, but the results are conservative compared with those based on observations. “If we wait until we have perfect models, we will have a 4 ºC [warmer] world or more until we start saying anything about the real-world impacts of climate change today,” she says.
Otto also notes that such analyses help to identify problems with the models, which allows the science to evolve. “If we would continue to just do projections but never test the models against real-world events we would make slower progress. That, in my view, is the true power of event attribution,” she says.

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