Almost 40% of land burned by western wildfires can be traced to carbon emissions

Almost 40% of forest area burned by wildfire in the western United States and southwestern Canada in the last 40 years can be attributed to carbon emissions associated with the world’s 88 largest fossil fuel producers and cement manufacturers, according to new research that seeks to hold oil and gas companies accountable for their role in climate change.

In findings published Tuesday in the journal Environmental Research Letters, the authors concluded that the emissions generated in the extraction of fossil fuels, as well as the burning of those fuels, have increased the amount of land burned by wildfire by raising global temperatures and amplifying dry conditions across the West. This growing dryness, or aridification, has caused the atmosphere to become “thirstier” for water, draining moisture from trees and brush and causing them to become more vulnerable to fire, the researchers say.

The study is the latest in a growing body of research known as extreme event attribution, or attribution science, which seeks to determine how much global warming has contributed to events such as heat waves, droughts and wildfires.

“We hope that people who are in communities that have been affected by wildfires will see this work and think about whether they want to hold these companies accountable,” said study author Kristina Dahl, principal climate scientist with the Union of Concerned Scientists.

To quantify the impact of the fossil fuel industry on wildfires, Dahl and her colleagues built on previous research that has shown that carbon emissions traced to the top 88 fossil fuel producers and cement manufacturers — including Exxon Mobil, BP, Chevron and Shell — have contributed significantly to the average temperature by which the Earth has warmed. (Cement production is responsible for 8% of human-generated carbon dioxide — significantly less than the burning of fossil fuels.)

The researchers found that changes in global mean temperature are positively linked with changes in the Western North American vapor pressure deficit, a measure of how effectively the air can dry out plants and vegetation that ultimately become fuel for wildfires, Dahl said.

“I actually laughed because I’ve never had such a strong correlation in my data before,” she said.

The researchers were then able to estimate that emissions from the major carbon producers contributed to 48% of the increase in the vapor pressure deficit observed over the last 120 years. Previous research has shown that this rise is strongly associated with an increase in burned forest lands in the western U.S. and southwestern Canada.

From there, the researchers found that the emissions were responsible for 37% of the 53 million acres of forest area — or 19.8 million acres — burned by wildfire since 1986.

The results don’t account for the effects of non-climate factors, including fire suppression, the prohibition of Indigenous burning and increases in human-sparked fires associated with more people moving into wilderness areas, which have played a role in driving the size and severity of individual fires, but have not affected the relationship between climate and burned area, the study notes.

Asked to comment on the findings, a spokesman for the Western States Petroleum Assn. said that “demonization” of the fossil fuel industry would not bring solutions.