Wildfires that have swept across America in recent years were caused by human-induced climate change and will get worse, researchers have warned.
Scientists used artificial intelligence to analyse fire patterns and climate data in the US over decades, and concluded that climate change is the leading cause of more wildfires.
Rong Fu, a UCLA professor of atmospheric and oceanic sciences and the study's corresponding author, said the trend was likely to worsen in the years ahead.
"I am afraid that the record fire seasons in recent years are only the beginning of what will come, due to climate change," she said.
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“Our society is not prepared for the rapid increase of weather contributing to wildfires in the American West."
The researchers analysed 'vapour pressure deficit', or VPD, the amount of moisture the air can hold when it is saturated minus the amount of moisture in the air.
Large wildfire-burned areas tend to have high vapour pressure deficits, conditions that are associated with warm, dry air.
The study found that the 68% of the increase in vapour pressure deficit across the western US between 1979 and 2020 was likely due to human-caused global warming.
The remaining 32% change, the authors concluded, was likely caused by naturally occurring changes in weather patterns.
The area affected by wildfires is increasing rapidly: in the 17 years from 1984 to 2000, the average burned area in 11 western states was 1.69 million acres per year.
For the next 17 years, through 2018, the average burned area was approximately 3.35 million acres per year.
In 2020, according to a National Interagency Coordination Center report, the amount of land burned by wildfires in the west reached 8.8 million acres.
Fu said she expected wildfires to continue to become more intense and more frequent.
"Our results suggest that the western United States appears to have passed a critical threshold – that human-induced warming is now more responsible for the increase of vapour pressure deficit than natural variations in atmospheric circulation," she said.
"Our analysis shows this change has occurred since the beginning of the 21st century, much earlier than we anticipated."
This year’s UN climate change report warned that extreme weather events like heatwaves and droughts that previously would have happened every 50 years could soon happen every four.
The report was the first to quantify the likelihood of extreme events across a wide variety of scenarios.
The researchers also warned that other ‘tipping point’ events were a possibility.
They wrote: "Abrupt responses and tipping points of the climate system, such as strongly increased Antarctic ice-sheet melt and forest dieback, cannot be ruled out."
Dr Robert Rohde, lead scientist of nonprofit land temperature organisation Berkeley Earth, said: "What were once-in-50-year heat extremes are now occurring every 10 years.
"By a rise of two degrees Celsius, those same extremes will occur every 3.5 years."
The report found that, for example, once-in-a-decade heavy rain events are already 1.3 times more likely and 6.7% wetter, compared with the 50 years leading up to 1900 when human-driven warming began to occur.
Droughts that previously happened once a decade now happen every five or six years.
Xuebin Zhang, a climatologist with Environment Canada in Toronto, warned that as the world warms, such extreme weather events will not just become more frequent, they will become more severe.
Zhang said that the world should also expect more compound events, such as heatwaves and long-term droughts occurring simultaneously.
"We are not going to be hit just by one thing, we are going to be hit by multiple things at the same time."
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