California wildfires: A window into how climate change fuels extreme events

The American continent has been engulfed by flames in recent years. Between January and February 2024, fires ravaged the forests and hills of South America, including a devastating megafire in Valparaíso, Chile. This year, in Los Angeles, California, wildfires have already scorched 160 square kilometers of land and homes, resulting in 24 fatalities and the evacuation of more than 150,000 people.

In the current crisis, it seems that almost everything is tied to climate change. However, California’s case is distinct. While there is no attribution study yet to determine the precise role climate change played in these specific fires — such analyses take time — a wealth of research over the past 20 years has highlighted how vulnerable the region is. It faces not only rising temperatures, but also a heightened likelihood of disproportionately severe wildfires.

“Fires have multiple causes, including human activity,” said Kaitlyn Trudeau, senior research associate for climate science at Climate Central, during a press conference. “I’m not going to go so far as to say that climate change caused this fire. But the important thing to understand is that it’s making them more dangerous.” In other words, due to the climate disruption driven by human activities, the likelihood of a fire escalating into a megafire has significantly increased.

For flames to spread under ideal conditions, several factors must align. Trudeau highlights three critical ones: rising temperatures, humidity, and winds. “Extreme heat is the event most directly influenced by climate change, and it plays a crucial role in explaining the fires in California,” she explained. In fact, the Office of Environmental Health Hazard Assessment (OEHHA) reported last year that average annual temperatures across the state have risen by about 1.4 degrees Celsius since 1895, with seven of the last eight years being the warmest on record.

Meanwhile, Trudeau notes, there is still no definitive evidence about the impact of climate change on the Santa Ana winds, although they have been stronger than usual this season. What is clear, she emphasizes, is that these winds have significantly amplified the flames, and are the reason why California is still on high alert.

What is happening in the U.S. state could be seen as a kind of laboratory. Several studies have been carried out on California, warning of its high vulnerability. In 2015, researchers published findings that human emissions had increased the likelihood of dry years coinciding with warm ones in California, which partly explained the severe drought the state experienced at the time.

By 2018, another study revealed that California’s annual wildfire burn rate had increased fivefold on 1972 figures. More recently, a 2022 study predicted that Southern California’s major fire seasons will lengthen due to climate change. From an average of 36 days per year between 1970 and 1999, fire seasons are projected to last 58 days annually by 2070–2099 under moderate emissions scenarios. If emissions rise sharply, the duration could extend to 71 days a year.

This crisis is not only climatic but also a public health emergency. In a statement from Stanford University, Lisa Patel, associate professor of pediatrics at the School of Medicine, warns that “wildfire smoke is about 10 times as toxic as the regular air pollution we breathe from the burning of fossil fuels.” Patel says this crisis reveals the perilous crossroads created by an energy system reliant on oil, gas, and coal, and relentless deforestation.

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