(Los Angeles) Climate change has become a major factor in the wildfires that regularly wreak havoc in the western United States, and a study released Monday at the opening of the COP26 conference on climate in Scotland found that human activity is a major cause.
In the American West, the area devastated by fires between 2001 and 2018 averaged 13,500 km.2 Per year, more than twice as much as in the period 1984-2000.
“It happened a lot faster than we expected,” he said Los Angeles Times Rong Fu, a meteorologist at UCLA University of California, led the study, which was published in the journal Journal of the United States National Academy of Sciences (Pnas).
In an attempt to understand the cause of this spectacular decline in such a short time, Mr.Me Fu analyzed various factors that work in the “vapor pressure deficit” (VPD), which reflects the dryness of the air.
VPD refers to the difference between the actual amount of water in the atmosphere and the maximum level that the latter can have. The greater the deficit, the more the surrounding air absorbs water from the soil and plants, creating more favorable conditions for fires.
Scientists have concluded that the increase in wildfires in the American West is closely linked to this deficit during the warm season. Between May and September, the number of days with high VPD increased by 94% between 2001-2018 compared to the previous period, the study said.
According to the calculations mMe According to Fu and his colleagues, “natural” climate variations accounted for an average of only 32% of this decline in VPD. The remaining (68%) increase in water deficit in the atmosphere over the last 20 years is due to global warming caused by human activities.
“Before 2000, we could describe fire-friendly weather using traditional weather patterns, but this is no longer the case,” Rong Fu told the LA Times.
According to some models, the study adds that anthropogenic warming, i.e. human origin, can explain 88% of the disorders observed in VPD.
In August 2020, when the largest fire in the California region – the August Complex Fire – burned nearly 4,200 km alone, anthropogenic warming caused almost half the deficit. The study concluded that the humidity was “exceptionally high”.
According to meteorologists, the planet has already risen almost 1.1 C since pre-industrial times, mainly due to the consumption of fossil fuels, due to human-produced greenhouse gases. Much of this warming has happened over the last 50 years.
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