The number of days with hot, dry, and windy weather—perfect for extreme wildfires—has nearly tripled worldwide in the past 45 years. The increase is strongest in the Americas, according to a new study. Scientists calculated that more than half of this growth stems directly from human-caused climate change.
This rise means that as global temperatures climb, multiple regions can face fire conditions at the same time. Experts call this synchronous fire weather, when several areas simultaneously have conditions ripe for wildfires. Countries may struggle to allocate firefighting resources, and neighboring nations might not help, as they could face their own fires, the study warns.
Rising risk of widespread fire outbreaks
From 1979 and for the next 15 years, the world averaged 22 days per year of synchronous fire weather. By 2023 and 2024, that number exceeded 60 days annually. “These changes increase the likelihood of fires that will be very challenging to suppress,” says John Abatzoglou, a fire scientist at the University of California, Merced, and co-author of the study.
The researchers focused on weather conditions rather than actual fires, analyzing heat, wind, dry air, and parched ground. “Weather raises the probability of widespread fire outbreaks, but it is only one factor,” says lead author Cong Yin, also a fire researcher at the University of California, Merced. Fires also require oxygen, fuel such as trees and brush, and an ignition source like lightning, human accidents, or arson.
Fire scientist Mike Flannigan of Thompson Rivers University in Canada, who did not join the study, calls it crucial research. Extreme fire weather is the primary driver of rising fire impacts globally. He adds that regions with historically staggered fire seasons could previously share resources, but now overlapping seasons increase pressure. “And that’s where things begin to break,” says Abatzoglou.
Fossil fuel emissions are fuelling fire weather
More than 60 percent of the global rise in synchronous fire weather days comes from climate change caused by burning coal, oil, and natural gas, Yin says. Researchers confirmed this by running computer simulations comparing actual climate trends to a hypothetical world without extra greenhouse gases from fossil fuels.
The continental United States averaged 7.7 synchronous fire weather days per year from 1979 to 1988. Over the last decade, that rose to 38 days annually, Yin reports. Southern South America faced even sharper increases. That region went from 5.5 days per year in 1979–1988 to 70.6 days annually over the past decade, with 118 days recorded in 2023.
Of 14 global regions studied, only Southeast Asia experienced a decrease in synchronous fire weather, likely due to rising humidity, Yin explains. This shift shows how climate change is reshaping fire patterns and straining firefighting resources worldwide.
