The study finds that more than half of the global rise in so-called "synchronous fire weather" days — when multiple regions experience dangerous fire conditions at the same time — can be attributed to human-driven climate change.
As global temperatures increase, areas that once faced fire seasons at different times of year are increasingly experiencing peak fire weather simultaneously. Researchers say this trend could undermine the long-standing practice of sharing firefighting personnel and equipment across borders.
The findings, published on 18 February in the journal Science Advances, suggest governments may face mounting challenges in responding to widespread outbreaks, particularly when neighbouring countries are battling their own emergencies.
Growing threat of widespread outbreaks
Between 1979 and the mid-1990s, large global regions experienced an average of about 22 days per year with synchronous fire weather. In 2023 and 2024, that figure exceeded 60 days annually.
"These changes significantly raise the probability of fires that are extremely difficult to contain," said study co-author John Abatzoglou, a fire scientist at the University of California, Merced.
The research focused on meteorological conditions — high temperatures, low humidity, dry soils and strong winds — rather than counting actual wildfire events. While weather is a critical driver, scientists emphasise that ignition sources and available fuel such as forests and grasslands also determine whether fires break out.
"It increases the likelihood of widespread fire outbreaks, but weather is only one component," said lead author Cong Yin, also of the University of California, Merced. Oxygen, vegetation and ignition sources ranging from lightning strikes to human activity remain essential elements.
Independent experts say the study highlights an often-overlooked dimension of wildfire risk. Mike Flannigan, a fire scientist at Thompson Rivers University in Canada who was not involved in the research, said extreme fire weather is the primary factor behind rising fire impacts globally. He noted that overlapping fire seasons reduce the ability of regions to pool resources.
"That's when response systems begin to falter," Abatzoglou added.
Climate change driving synchronised fire risk
Using climate models, researchers compared observed conditions over the past 45 years with simulations of a world without elevated greenhouse gas concentrations from fossil fuel use. They estimate that more than 60% of the global increase in synchronous fire weather days is linked to emissions from coal, oil and natural gas.
Regional data reveal sharp increases in several parts of the world. In the continental United States, the annual average of synchronous fire weather days rose from 7.7 between 1979 and 1988 to 38 over the past decade.
The shift is even more dramatic in southern South America. That region recorded an average of 5.5 such days annually in the 1980s, compared with 70.6 days per year in the last decade. In 2023 alone, it experienced 118 days of overlapping high-risk conditions.
Of 14 global regions analysed, only Southeast Asia showed a decline in synchronous fire weather days, a trend researchers attribute to increasing humidity in parts of the region.
Scientists caution that as climate change continues to intensify, the likelihood of concurrent extreme fire conditions across continents may rise further, complicating disaster response efforts and increasing the risk of widespread environmental and economic damage.