When the Thomas fire moved through Ventura and Santa Barbara counties in December 2017, Danielle Touma, at the time a Stanford earth science researcher, was amazed at how bad it was. Burning for more than a month and showering 440 square miles, the fire was then considered the worst in California history.
Six months later the Mendocino Complex Fire set that record and covered 717 square miles over three months. Since then California wildfires have been normal, with five of the top 10 occurring in 2020 alone.
The worrying move raised some questions for Touma, who is now a graduate researcher at UC Brab Santa Santa School for Environmental Science & Management.
“Climate scientists knew there was a climate signal but we didn’t really understand the details about it,” she said of the transition to a more climate-friendly climate for wildfires. Although research has long concluded that it has anthropogenic activity and its effects – including greenhouse gas emissions, combustion of biofuels, industrial aerosol (aka air pollution) and modifications the land use – taking the risk of extreme weather, the specific roles and these effects actions were not yet clear.
So far. In the first study of its kind, Touma, with Bren School co-researcher Samantha Stevenson and colleagues Flavio Lehner from Cornell University and the National Center for Atmospheric Research (NCAR), and Sloan Coats from the University of Hawaii, have discovered anthropogenic effects competitive measure of the real risk of recent and imminent fire weather. By eliminating the influence of these man-made factors, the researchers were able to find out what roles these actions have played in generating a climate that is increasingly friendly to fire around the world and the threat of serious fires in the coming decades.
Their work appears in the magazine Nature Communication.
“By understanding the different components of these scenarios of future climate change, we will gain a greater awareness of the risks involved in each of these components, as we know there will be uncertainty in the future, “Stevenson said.” And we know that these risks will be unfairly expressed in different places as well, so that we are better prepared for the parts of the world that would be more vulnerable. “
Warm, dry and windy
“To get a wildfire to light and spread, you need suitable weather – you need warm, dry and windy weather,” Touma said. “And when these conditions are at their highest, they can ignite real fires. cause great. “
Using modern climate model simulations available from NCAR, the researchers analyzed the climate under different combinations of climate influences from 1920-2100, allowing effects individual and their impact on the real risk of fire weather.
According to the study, greenhouse gas emissions (which began to rise rapidly before the middle of the century) were a major contributor to global temperatures. In 2005, real-time fire risk emissions raised 20% from preindustrial levels in western and eastern North America, the Mediterranean, Southeast Asia and the Amazon. The researchers estimate that, by 2080, greenhouse gas emissions are expected to increase the risk of a real wildfire by at least 50% in western North America, the African zone. central, southeast Asia and Australia, and doubling in the Mediterranean Sea, southern Africa, eastern North America and the Amazon.
At the same time, the burning of biofuels and land use changes that contribute to greenhouse gas warming have a greater regional impact, according to the study – specifically a 30% increase in the real risk of fire weather across the Amazon and western America in the 20th century caused by the burning of biofuels. Land use changes, the study found, also predicted severe weather in western Australia and the Amazon.
Protected from pollution?
The role of industrial aerosolization has become more complex in the 20th century, in fact reducing the risk of real fire weather by about 30% in the Amazon and the Mediterranean, but increasing it by at least 10% in Southeast Asia and Northwest America, the researchers said. lorg.
“(Industrial aerosol) prevents some of the sun’s radiation from reaching the earth,” Stevenson said. “So they tend to have a cooling effect on the climate.
“And that’s part of the reason we wanted to do this study,” she continued. “We knew there had been something compensating in a way for greenhouse gas heating, but not details on how that compensation might continue in the future.”
The cooling effect may still be present in regions such as the Horn of Africa, Central America and the Northeast Amazon, where aerosol has not been reduced to pre-industrial levels. Aerosols may still compete with the effects of greenhouse gas warming in the Mediterranean Sea, western North America and parts of the Amazon, but researchers expect this effect to be spread across most of the world by 2080, as a result of cleanup efforts and increased greenhouse gas-led warming. Northeast America and Europe are likely to see warming and drying out as a result of aerosol depletion first.
At Southeast Asia, “where aerosol emissions are expected to continue,” there may be a weakening in annual monsoon, drier conditions and an increase in severe fire weather. danger.
“Southeast Asia is dependent on the monsoon, but aerosol causes so much cooling on land that it can suppress monsoon,” Touma said. “It’s not just whether you have aerosol or not. no, it’s how the regional climate interacts with aerosols. “
The researchers hope the detailed insight their study offers opens the door to more advanced investigations of the Earth’s changing climate.
“In the wider range of things, it ‘s important for climate policy, as if we want to know how global actions affect climate,” Touma said. “And it’ s also important. to understand the potential impacts on people, such as urban planning and fire management. ”
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