Wildfires are burning longer each day in North America as human-caused climate change extends the warm, dry conditions that fuel them, according to a study published Friday in Science Advances. The number of hours when weather conditions favor wildfires has increased 36% over the past 50 years, with some regions like southwestern New Mexico and central Arizona seeing as much as 2,000 additional burning hours annually.
The shift means fires no longer reliably die down at night, creating longer and tougher-to-fight blazes while threatening communities during hours when firefighting operations are most difficult.
How the Fire Pattern Has Changed
Wildfires that once died down when darkness fell now burn through the night and into the early morning. The increase varies by region. In California, potential burning hours have increased by 550 since the mid-1970s. Southwestern New Mexico and central Arizona have gained up to 2,000 additional burning hours per year — the highest increase documented by researchers.
The calendar extended as well. The number of days each year when weather conditions favor wildfires has increased by 44% — effectively adding 26 days to fire season over the past half century.
Recent fires exemplify the new pattern. The Lahaina fire in Hawaii ignited at 12:22 a.m. in 2023. The Jasper fire swept through Alberta in 2024 at night. The Los Angeles wildfires burned through the night in 2025.
Xianli Wang, a fire scientist with the Canadian Forest Service, described the shift plainly: “Fires normally slow down during the night, or they just stop. But under extreme fire hazard conditions, fire actually burns through the night or later into the night.”
The Science of Warming Nights
The mechanism is straightforward. Nights warm faster than days in a climate altered by heat-trapping gases from fossil fuel burning. Those gases create a blanket effect, absorbing and re-emitting heat downward.
Since 1975, summer nighttime temperatures in the contiguous United States have risen 2.6 degrees Fahrenheit (1.4 degrees Celsius). Daytime temperatures have risen 2.2 degrees Fahrenheit (1.2 degrees Celsius). The difference may seem small; for wildfires, it is decisive.
Kaiwei Luo, the lead researcher at the University of Alberta, found that nighttime humidity “doesn’t rebound” from daytime dryness the way it once did. In a drought, warmer air pulls more moisture from ground and plants, leaving fuel drier and more flammable.
The study analyzed nearly 9,000 larger fires from 2017 to 2023 using weather satellites and hour-by-hour atmospheric data. Researchers then applied the patterns to historical data spanning Canada and the United States from 1975 forward, documenting a shift in the fundamental rhythms that once governed wildfire behavior.
Operational and Statistical Consequences
John Abatzoglou, a fire scientist at UC Merced, noted that “nights aren’t what they used to be — that is, more reliable breaks for wildfire.”
Safety hazards compound the operational burden on wildland firefighters. Wildland firefighter Nicholai Allen, who also founded a firm making fire prevention tools, said it is very difficult to fight fires at night. “You have to understand that you have snakes and bears and mountain lions and all the stuff you have in daytime,” Allen said. “But at night, they’re really scared and they’re running away from the fire.” A colleague, he noted, was bitten by a bear while fighting a nighttime blaze.
The expanding window for fire and the extended season show in burn statistics. From 2016 to 2025, wildfires in the United States burned an average of 11,000 square miles per year — 2.6 times the average of the 1980s. Canada’s average land burned in the last decade is 2.8 times more than during the 1980s.
Jacob Bendix, a fire scientist at Syracuse University, called the study “a sobering reminder of climate change’s role in driving increased fire potential across almost all of the fire-prone environments of North America.”