California plans to thin out millions of acres of its forests to lessen the risk of destructive wildfires. But such efforts may not be moving fast enough to make up for the influence of climate change.
There are two main reasons California鈥檚 wildfires are growing larger and more damaging: hotter and more volatile weather due to climate change, and the buildup of vegetation in forests due to centuries of fire suppression, which acts as fuel when a blaze does strike.
鈥淭he big reason we have such a strong climate signal in this is because there鈥檚 just so much fuel,鈥� says at the Pennsylvania State University.
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In 2021, California set the goal of reducing this forest fuel across 4000 square kilometres (1 million acres) per year by 2025, and more than doubling the treated area by 2045. But so far, California鈥檚 efforts may not be enough to entirely counter the effects of climate change.
at the Breakthrough Institute, an environmental think tank in California, and his colleagues modelled how different amounts of fuel reduction would change the intensity of fires 鈥� an important measure of impact, related to how quickly a wildfire spreads and how much it destroys.
They used data on more than 27,000 past blazes to train their model on how weather, available fuel and other factors influence intensity. 鈥淥nce those models have learned that relationship, then you can turn the knob on various things,鈥� says Brown, such as climate change under different carbon emissions scenarios.
According to the model, without any fuel reduction efforts, average fire intensity would increase by around 14 per cent between now and 2050, and by 25 per cent by 2090, due to warmer conditions under a moderate emissions scenario.
When fuel reduction was incorporated over a large enough area, however, they found it was able to erase that effect: treating around 2500聽km2 of forest per year would undo the climate-driven increase in average fire intensity by 2050, and treating 6500 km2 per year would be enough by 2090.
Although it wouldn鈥檛 be practical, treating all of the state鈥檚 forests would cut fire intensity almost in half relative to today, even with the amount of warming expected by the end of the century, they found. 鈥淭hese results are really encouraging, that [fuel reduction] is effective in the face of warming,鈥� says Brown.
This seems to suggest the state鈥檚 current efforts on this front would be enough to erase the influence of climate change on wildfire severity out to around 2050, says Brown. According to the California Department of Forestry and Fire Protection (Cal Fire), in 2023 鈥� the most recent year with complete 鈥� state and federal agencies and other efforts led to treatments on around 2800 km2.
However, this figure may not tell the whole story. The researchers鈥� model assumed that both prescribed burning and mechanical thinning would be carried out on all treated land. But a far smaller area in California received both.
In 2023, state, federal and other efforts led to prescribed burns on only about 1000 km2 and thinning on about 2300 km2, with limited overlap. And the rate of treatment this year, at least by the state via Cal Fire, has seen a slowdown. Cal Fire says it expects to treat just 400 km2 in total this year, down from 635聽km2 in 2023 and just under 560 km2 last year.
鈥淭hat鈥檚 pretty low,鈥� says Taylor, adding that efforts to expand treatments face practical barriers. However, he says the numbers could look better if the state counted wildfires themselves 鈥� which burned 聽in 2024 鈥� as a form of unintentional fuel reduction. 鈥淐alifornia isn鈥檛 necessarily behind if they think about it that way,鈥� he says.
Environmental Research Letters
