Increasingly frequent and intense wildfires in the western United States during the past two decades are strongly linked to anthropogenic climate change, according to research led by the University of California, Los Angeles (UCLA) and the Lawrence Livermore National Laboratory.
Data from the U.S. Geological Survey shows that recent decades witnessed a dramatic increase in destruction caused by wildfires in the western United States. From 1984 to 2000, the average area burned across 11 western states was 1.69 million acres per year. In the past two decades, the average area increased to 3.35 million acres annually. In 2020, the area of land burned by wildfires reached a staggering 8.8 million acres.
However, the factors leading to this massive increase have been subject to debate. While some scientists claim that human-induced climate change was the lead cause of increased wildfires frequency, others linked the events to changing weather patterns, natural climate variation, and factors such as forest management, reduced summer rains, or earlier spring snowmelt.
By applying artificial intelligence to analyze climate and fire data, the researchers found that 68 percent of the increase in vapor pressure deficit (a leading cause of wildfires) across the western U.S. has likely been caused by anthropogenic climate change. “And our estimates of the human-induced influence on the increase in fire weather risk are likely to be conservative,” said study lead author Rong Fu, a professor of Atmospheric and Oceanic Sciences at UCLA.
“Our results suggest that the western United States appears to have passed a critical threshold -that human-induced warming is now more responsible for the increase of vapor pressure deficit than natural variations in atmospheric circulation,” she added. “Our analysis shows this change has occurred since the beginning of the 21st century, much earlier than we anticipated.”
The scientists expect wildfires to continue to become more frequent and intense, even though cooler and wetter conditions may offer occasional respite. “I am afraid that the record fire seasons in recent years are only the beginning of what will come, due to climate change, and our society is not prepared for the rapid increase of weather contributing to wildfires in the American West,” concluded Professor Fu.
The study is published in the journal Proceedings of the National Academy of Sciences.