The blame game: how responsible are we for the recent wildfires?

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This summer, the western United States experienced a truly devastating wildfire season. Across the country, more than 48,000 forest fires raged, damaging more than six million hectares of land. It would be nice to think that humans were not the main cause of these events and that natural changes in weather conditions have contributed to drought and fires in parts of the world.

But the reality is not so good. Climate change is likely the cause of wildfires, according to new research that aimed to quantify how much we can blame natural causes for the increasing rates of wildfires in the western United States. “We want to know to what extent this increase in fire weather conditions only changes the weather conditions and to what extent cannot be explained by changing weather conditions,” said Rong Fu, one of the authors of the report. article and professor in the Department of Atmospheric and Oceanic Sciences at UCLA. Ars.

The research began about a year ago. Fu and some of his colleagues live in California and have all been affected by the wildfires, so they wanted to investigate their causes.

Is that bad ?

Fu and his team deployed a technique called “ensemble-constructed flux analog”. In short, they looked back between 1979 and 2010 in the region and found instances in which the natural weather looked a lot like what it is now. From there, they looked at a number called vapor pressure deficit (VPD) – basically how dry and “thirsty” the area is – in both historical and modern cases.

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VPD is the leading cause of wildfires on the West Coast of the United States and in many other places around the world. So if the modern VPD is higher than it was in historical cases with similar weather conditions, that would suggest that there is an unnatural component in how things are currently prone to fires. “Basically the difference between [the present VPD] and the [VPD] we can get the same weather conditions in the past is due to climate change, ”she said.

Fu noted that these cases will not have the same weather conditions, however. She also added that the work took into consideration various other factors that could have played a role, such as changes in vegetation.

In total, research suggests that only about 32 percent of VPD tendencies can be attributed to natural causes. The remaining 68 percent or so cannot, and climate change is likely to be the cause.

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To make matters worse, 68 percent is a conservative estimate. The document notes that the number could reach 88 percent. Fu noted that the past weather data used by his team was likely also affected by humans emitting carbon and busying themselves with the climate even then. “The base period is already affected by greenhouse gases,” she said.

As a result, their estimates of the impacts of climate change are not as large as they actually would be; this is on the more conservative side of things. “We want to be as conservative as possible. So when we say, “Climate change contributes two-thirds of [the increase to] fire times, “we know that is probably true and that this is just an underestimation of climate change,” she said.

Trying to determine exactly how much human activity has an impact on climate change is a tricky business, as the climate itself changes to some extent. But this research is another step towards understanding just how responsible humans are. In addition, according to Fu, the methods used in this article could be deployed elsewhere in the world. “I think this approach can be generalized to other areas,” she said.

PNAS, 2021. DOI: 10.1073 / pnas.2111875118 (About DOIs)

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