Global warming is a major culprit in wildfires in the American West

Climate change has become the primary factor responsible for the wildfires that regularly sweep the western United States, and human activities are largely to blame, according to a study released Monday as the COP26 climate conference opened in Scotland.

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In the American West, the average area destroyed by fires between 2001 and 2018 was 13,500 square kilometers per year, twice the area of ​​1984-2000.

“It happened much faster than we expected,” Rong Fu, a climate scientist at the University of California, UCLA, who led the study published in the Journal of the National Academy of Sciences, told Pnas. ).

In an effort to understand what contributed to this astounding decline in such a short time, the team of American researchers led by Ms. Fu analyzed the various factors at work in the “vapor pressure deficit” (VPD in English), which reflects drought. from the air.

VPD represents the difference between the amount of water actually present in the atmosphere and the maximum that the latter can contain. The greater this deficiency, the more water is absorbed by the surrounding air from the soil and plants, creating conditions that are increasingly conducive to fires.

Scientists have proven that the increase in wildfires in the American West is closely related to this deficit during the hot season. Between May and September, the number of days with elevated VPD increased by 94% during 2001-2018 compared to the previous period, according to the study.

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According to Ms Fu and colleagues’ calculations, “natural” changes in the atmosphere played only a role in the deterioration of VPD, at an average of 32%. The remaining (68%) of this sudden rise in the atmospheric water deficit over the past 20 years is attributed to global warming, caused in large part by human activities.

“Before 2000, we could explain the weather conducive to fires only using traditional weather models,” Rong Fu said in the Los Angeles Times, but that is no longer the case.

According to some models, the study adds, anthropogenic warming, that is, of anthropogenic origin, can explain up to 88% of the anomalies observed in VPD.

The study concluded that in August 2020, when California suffered the largest recorded fire in the region – the August Composite Fire – which alone burned nearly 4,200 square kilometers, human warming was responsible for nearly half of its “exceptionally high” moisture deficit. “.

According to climate experts, due to greenhouse gases generated by humans, particularly through the consumption of fossil fuels, the planet has already gained about 1.1°C since the pre-industrial era. Most of this warming has occurred in the past 50 years.

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