Summer and autumn are extremely warm. The winter is unusually dry. The slopes are covered with bone-dry vegetation. There are also strong Santa Ana winds.

Scientists say that among the conditions that contributed to the most destructive fires in Los Angeles history, a significant factor was human-caused climate change.

A team of climate scientists at UCLA said in a report analyze This week, if you break down the reasons for the extreme dryness of vegetation in Southern California at the time of the fires, global warming may have been responsible for about a quarter of that dryness, one of the factors fueling the explosive spread of the fires. They say the intense heat of summer and fall dries out shrubs and grasses on hillsides, making these fuels burn more violently once ignited.

Scientists say that without the higher temperatures brought by climate change, the fires would still be severe but would be "smaller and less intense."

Climate scientist Park Williams prepared the study with UCLA colleagues Alex Hall, Gavin Madakumbura and others Analyzing it, he said, the conditions that made such a catastrophic fire possible were like three switches turning on at the same time. Climate and Wildfire Research Program.

"These switches were very high fuel loads, very dry fuel and very strong Santa Ana wind events," Williams said. "All of that, mostly just bad luck."

But because all of these natural switches line up, he said, "now, because of climate change, the atmosphere is warmer and the fuels are drier than before, so the fires are more intense and bigger than they used to be." That's not how it is. "

More detailed peer-reviewed studies examining the effects of climate change and natural factors will take time, the scientists said, and they prepared the analysis as a starting point for deeper research.

Williams and his colleagues studied the past two wet winters, which nourished the growth of shrubs and grasses in Southern California. They pointed out that research has More extreme atmospheric river storms expected But so far, that trend has not shown up in data from the western U.S. due to global warming, making the impact of climate change during the past two wet years "highly uncertain."

They analyzed unusually dry conditions in Southern California, which has not seen significant rain in eight months. One weather station in Los Angeles recorded just 0.29 inches of rainfall from May 1 to January 8, the second driest year since 1877, behind only 0.15 inches in 1962-63. However, the extent to which climate change may have contributed to the unusually long dry spells remains "highly uncertain", the researchers said.

However, scientists say the unusually hot summer and fall of 2024 are part of a clear trend of rising temperatures due to man-made climate change.

The summer and fall seasons were the third warmest in the region since 1895 and occurred in U.S.G. Confirmed to be the hottest on earth Records have been kept since 1880.

High temperatures in Southern California appear to be partly responsible for a sharp decline in the "fuel moisture" of dead vegetation, researchers say. By January, the state had become one of the driest on record, and those conditions were "extremely conducive to wildfires." occur".

They estimate that abnormal heat is responsible for about 25 percent of the dry vegetation, while lack of rainfall is responsible for the other 75 percent.

When strong Santa Ana winds arrived on January 7, as they sometimes do this time of year, they brought with them the final impact of a variety of factors that set the stage for high fire danger.

"The most obvious way climate change is affecting fires in the western United States and California is through the direct impact of rising atmospheric temperatures," Williams said. previous research and Other research. "A warmer atmosphere is a thirstier atmosphere, so all else being equal, fuels will dry out faster in a warmer world."

Other scientific studies have found that human-caused warming leading to more severe drought and contribute Bigger, more intense wildfires in the western united states

However, Williams said there are important differences between areas where fires occur in forests rich in vegetation fuel and areas like Southern California, where fires often burn sparse shrubs and grasses.

In recent years, there has been a trend toward larger wildfires across California. But along the Southern California coast, data show there has been no trend toward larger fires over the past four decades, and the number of fires has actually declined over that period—possibly because people have become more wary of accidents. careful. Or it could be that conditions have become drier on average over the years, causing vegetation to become sparse, Williams said.

"What you see is most years there are almost no fires and some years there are a lot of fires," Williams said. "Every once in a while, Southern California gets unlucky and all three switches turn on at the same time. "

Some studies predict that in a hotter, drier future, dry ecosystems in the West, such as much of Southern California, may have fewer fires on average, as drier conditions reduce the amount of flammable vegetation. However, Southern California is still likely to experience intermittent wet years, resulting in more vegetation growth. As these fires illustrate, Williams said, "the wetter it was the previous year, the more fires there are the next year."

"In those rare years when all factors come together to fuel wildfires, atmospheric warming due to human-caused climate change is likely to make many fuels drier than they would otherwise be," Parker said. "This will make fires in these infrequent years cooler than they would otherwise be." Conditions become bigger and more violent.”

The cause of the fire is under investigation, and scientists note that since there are no natural sources of fire at this time of year, it is almost certainly caused by fire. Started by human activities In some way - whether it's sparks from power lines, fireworks, arson or something else.

The UCLA team prepared the analysis in tense days as they watched the damage unfold and heard from friends and colleagues who were evacuating or whose homes had burned.

This week, professors are teaching online college decision Poor air quality on campus due to wildfire smoke.

"This is fundamentally a natural disaster. Once a fire is ignited, we do live in a place where a truly extreme event occurs," said Hall, another climate scientist who prepared the analysis.

"Climate change is exacerbating this to some degree. We can't quite quantify it, but it's there," Hall said. "We know that warmth dries out vegetation. We know that part of the lack of moisture during fires can be attributed to abnormal warmth."

Without the effects of climate change, he said, "it would probably be smaller and easier to fight."

Hall said a deeper look into the effects of global warming will involve research that further digs into the complex dynamics of fires, weather conditions and rising temperatures.

These and other attribution studies are becoming increasingly important as California, Hawaii and other states sue oil companiesseeking billions of dollars in damages for impacts related to burning fossil fuels.

Julie Kalansky, a climate scientist and associate director of the Western Center for Weather and Water Extremes at the Scripps Research Institute at the University of California, San Diego, said trends observed in recent decades related to anthropogenic warming are Summer temperatures rise and vegetation dries. oceanography.

she pointed Research Research shows that rising temperatures in recent decades have brought about an increase in "evaporative demand," drawing more moisture from landscapes across the western United States, a finding that the authors say points to the need to plan for increased wildfire risk.

As for the Los Angeles fires, Kalansky said more research is needed to better understand the impacts of climate change and "to be able to provide some clearer numbers on this."

As climate change continues, "more severe wildfires are expected to occur when all other conditions necessary for fires occur," the UCLA scientists wrote.

They called for wildfire mitigation efforts to focus on "the factors we can control and the damage we can prevent," such as preventing fires during fire weather, adopting strategies that prevent homes from burning easily, and planning in areas with lower fire risk development.

Scientists can also play an important role in identifying areas that should be avoided from fires because of their location or exposure to combustible vegetation, Williams said.

"In the long term, when all factors align, understanding that these types of extreme events do occur here should hopefully guide decisions about where to rebuild," he said. "There are some places where fire danger becomes high again when fuels return. Very high.”