Conditions that fueled L.A. fires were more likely due to climate change, scientists find
Climate change increased the likelihood of the extreme conditions that allowed the recent fires to roar across the Los Angeles area, an international group of scientists said Tuesday.
The hot, dry and windy conditions that preceded the fires were about 35% more likely because of human-caused global warming, according to a new report from the World Weather Attribution group, which analyzes the influence of global warming on extreme events.
The fires, which started during a ferocious windstorm and after almost no rain had fallen in greater Los Angeles since the spring, have killed at least 29 people and torched more than 16,000 buildings, including homes, stores and schools.
'This was a perfect storm when it comes to conditions for fire disasters — the ingredients in terms of the climate enabling, the weather driving the fires and the huge built environment right downwind from where these ignitions occurred,' John Abatzoglou, a professor of climatology at the University of California, Merced, who contributed to the report, said at a news conference.
Compared to a preindustrial time before fossil fuels were widely used, there are now 23 extra days of 'dry season' on average each year in the Los Angeles region, the report said, making it more likely that fires will coincide with seasonal Santa Ana winds.
Park Williams, a professor of geography at the University of California, Los Angeles, and an author of the report, said fires during cool seasons in Southern California require four conditions: widespread grass or brush that can burn; abnormally dry conditions; an ignition (which almost always comes from a person); and extreme weather, like the recent windstorm. He described each of these conditions as an individual switch in a system that requires all four to be flipped on in order for light to emanate.
'The artificial warming due to human-caused climate change is making the light brighter,' Williams said.
The authors of the report analyzed weather and climate models to evaluate how a warmer atmosphere is shifting the likelihood of fire weather (meaning conditions that increase the risk of wildfire). They also tracked how a metric called the Fire Weather Index changed over time. The index tracks temperature, relative humidity and wind speeds, all factors that contribute to the likelihood of fire.
The researchers found that the kind of conditions that drove the L.A. area fires are expected to occur on average once in 17 years in today's climate. Such conditions would have been expected once every 23 years without climate change and would have been less extreme when they did occur, the report says.
As a group, World Weather Attribution is a loose consortium of scientists who publish rapid findings about climate change's role in extreme weather events. Although their research methods are peer-reviewed, this specific rapid analysis has not been through the rigor of a typical academic review process, which can take months or longer. The group's prior analyses of heat, wildfire and hurricane disasters have held up to scrutiny after initial release and were ultimately published in academic journals.
For climate attribution scientists studying how much climate change is to blame for specific events, wildfire disasters are notoriously challenging to untangle, and local nuances are extremely important.
In the case of the recent California fires, the report's authors found that although climate change played a role, it was not the sole factor.
The hillsides surrounding Los Angeles are filled with brush that has evolved to burn with regularity, and more people are in these areas today than in the past to potentially start fires via cigarettes, power lines, fireworks, vehicles or other sources. Additionally, neighborhood development has pushed deep into areas prone to burn, which means houses are serving as fuel for wildfires and contributing to its rapid spread.
'Fire in Southern California is highly complex, right? It's a combination of a number of things. This is a landscape that's got a really distinct human imprint on it,' Abatzoglou said, adding that the Los Angeles region has 'a large population, a lot of ignitions, a lot of land-use related issues.'
The influence of climate change on the Santa Ana winds, one of the driving factors behind the Los Angeles fires, remains murky. The report's authors said that some research suggests the winds will become less intense as the climate warms; however, other research suggests this wind pattern will persist and perhaps intensify during the cold months.
'We don't know of a direct mechanism that would link climate change to the winds, but there could be," Williams said. "We just don't know."
This article was originally published on NBCNews.com
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USA Today
4 days ago
- USA Today
A fog-free San Francisco? Scientists ponder California's climate future
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Yahoo
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- Yahoo
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Time Magazine
30-05-2025
- Time Magazine
Why ‘Hundred-Year' Weather Events Are Happening More Than Once Every 100 Years
Climate change is leading not only to droughts, wildfires, and extreme weather. It's also leading to oxymorons—at least when it comes to what are known as hundred-year storms, floods, and other events. Long-term weather forecasting—the kind that predicts conditions months or even years or decades in advance—is all about probabilities, factoring together not only current conditions and trends, but the historical record. An area that has seen floods in the past when the spring was unusually rainy or tropical storms were unusually fierce, is likely to see them again if the same conditions recur. Ditto the likelihood of severe storms when the atmosphere is holding a lot of moisture and the oceans are atypically warm. Environmental scientists have gotten so good at reading weather history that they can characterize some severe storms or floods as likely to occur in a given area only once in 100 years—or even 500 years or a thousand years. That's where the oxymoron comes in. 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By definition, a hundred-year storm has a 1% likelihood of occurring in any one year; for a 500-year storm it's 0.2%; for a thousand years it's 0.1%. But every year the probability clock starts anew; if the 1% longshot comes in and a hundred-year storm occurs on the Carolina coast in 2025, that same area would typically have the same 1% chance in 2026—but climate change is making the likelihood even higher. 'It's not like you can calendar one of these events and say you're cool for another 100 years,' says Pershing. Driving the more frequent events is what Pershing describes as a 'thirstier' atmosphere, one that is hotter and thus capable of holding more moisture. 'We have a supercharged water cycle and that means that when you get a rain event it has a better chance of being a bigger event than it used to be,' says Pershing. Some of those bigger events could be coming soon—in the form of hurricanes. 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'As we witnessed last year with significant inland flooding from hurricanes Helene [in September] and Debby [in August], the impacts of hurricanes can reach far beyond coastal communities,' said acting NOAA administrator Laura Grimm in a statement. Things could get dicey not only in the Atlantic, but in the Pacific as well. Already, tropical storm Alvin is forming off the southwest coast of Mexico, two weeks ahead of the start of the eastern Pacific hurricane season. In addition to hurricanes, floods, and storms, heat waves, droughts, and wildfires can be projected out over centuries. 'A hotter atmosphere can hold more water, but if you squeeze that moisture out over a mountain range like what happens in the west, then you end up with a much drier air mass,' says Pershing. 'The atmosphere then wants to suck the moisture out of the ground and so droughts get more severe.' There's no easy fix for a feverish atmosphere. In the short run, adaptation—dikes and levees to protect flood-prone cities, relocating residences away from eroding coasts—can help. In the longer run, shutting off the greenhouse emissions that created the problem in the first place is the best and most sustainable bet for limiting hundred-year storms to their hundred-year timelines. 'We have to quit fossil fuels as fast as we can,' says Pershing. 'This will give the climate a chance to stabilize and us a chance to adjust.'
