The United States is facing one of its most severe wildfire seasons in recent memory, with fires consuming millions of acres across multiple states. The crisis forms part of a broader global pattern in which hot, arid conditions — increasingly linked to climate change — are creating environments far more conducive to destructive blazes. U.S. wildfire seasons have lengthened over recent decades, with the Forest Service and other agencies now routinely treating what was once called "fire season" as a near-year-round challenge.

In Washington state, fires that ignited over the weekend in and around Spokane have destroyed hundreds of structures and displaced more than 60,000 residents, equivalent to roughly 10% of the local population. According to InciWeb, a federal fire-tracking database, three major fires have scorched upward of 8,000 acres and remain entirely uncontained. Washington Public Lands Commissioner Dave Upthegrove confirmed on Monday that 17 fires are currently active across the state.

The global picture is equally grim. Ongoing wildfires in Greece have burned tens of thousands of acres and prompted widespread evacuations. These follow historic fires in France and Spain last month that displaced hundreds of thousands of residents, part of a broader European wildfire crisis this summer.

A Shared Underlying Driver

Though these fires erupted across vastly different regions and ecosystems, scientists say they reflect the same fundamental shift: rising global temperatures are intensifying wildfire risk through two simultaneous mechanisms. First, regions historically prone to fire are growing hotter and drier. Second, landscapes once considered at low risk are increasingly capable of sustaining destructive blazes.

"We're seeing both, in the same moment, in different places, in different ecosystems," said Daniel Swain, a climate scientist at the University of California who specializes in wildfire research. "The commonality between all of them is that there has been a substantial period of record-breaking warmth and/or dryness."

Swain characterizes this phenomenon as "lifting the flammability veil" — a metaphor for how global warming is pushing previously marginally flammable landscapes past the threshold needed to sustain large fires.

Noah Diffenbaugh, a professor of Earth system science at Stanford University, said global warming is "putting a thumb on the scale, producing severe and unprecedented heat waves." Some parts of the world have long been susceptible to burning but rarely experienced the sustained heat and aridity necessary to fuel major conflagrations.

Ecosystems Under Stress

Extended periods of exceptional heat and dryness progressively strip trees of moisture, rendering them increasingly combustible. The effect is especially pronounced in ecosystems that evolved under relatively cool, damp conditions — including Canada's boreal forests, California's Sierra Nevada, and parts of temperate Europe. Unlike forests in the American Southwest, where species have adapted to seasonal drought and recurrent fire, these ecosystems can transform into tinderboxes after just weeks of unusual heat.

Mojtaba Sadegh, a wildfire researcher at Boise State University, drew a parallel between the cumulative impact of heat waves on landscapes and their toll on the human body. Successive days of extreme heat, he noted, are far more dangerous than a single hot day.

"The physiology of the human body takes several days to kick in," Sadegh said. "The same happens with vegetation."

In a study published last month in the journal Nature Communications Earth & Environment, a team of researchers including Sadegh identified "fire weather waves" — prolonged episodes of exceptionally hot, dry, and often windy conditions. They found that global forest regions experienced such waves on an average of 4% of all days between 1979 and 2024. Yet those waves coincided with more than a quarter of all land area burned and nearly half of the most energetic forest fires recorded. The researchers determined these episodes have grown more frequent across most regions since 1979 and projected that the trend will persist.

Warning Signs Were Early

Indicators of an active U.S. fire season emerged as early as April, when aerial firefighting tanker units were already heavily engaged. By June, the National Interagency Fire Center had issued warnings that the Pacific Northwest and Northern California faced a potentially severe fire year.

A critical factor was last winter's snow drought across the Pacific Northwest, the Rocky Mountains, and large portions of California. Mountaintops that typically accumulate feet of snow remained bare, depriving the landscape of its natural spring and early-summer replenishment. The absence of snowmelt left grasses and shrubs desiccated and starved trees of essential moisture.

Paradoxically, extreme precipitation also contributes to elevated fire risk. Heavy downpours promote rapid vegetation growth that later dries out and becomes potent fuel. Swain pointed out that Spain experienced torrential rains in February before this summer's heat waves arrived.

"That is the same sequence of events that led up to the Los Angeles fires in 2025," he said.

Strained Resources and New Vulnerabilities

The simultaneous eruption of fires across multiple continents is constraining the ability of nations to assist one another by sharing firefighters and equipment. Countries including the United States, Greece, and Spain have long relied on international mutual-aid agreements that allow crews and aircraft to cross borders during peak demand — arrangements now stretched thin by overlapping crises. Communities that never anticipated needing evacuation plans or fire mitigation measures are being forced to reassess. Smoke from large blazes can travel thousands of miles, degrading air quality far from the flames — a phenomenon observed during Canada's record 2023 fire season, when haze drifted across the eastern United States and Europe.

Climate change does not mean every corner of the globe will adopt California's fire profile — the state is itself battling multiple wildfires this week amid a heat wave. Rather, it signals that more landscapes worldwide will intermittently cross a threshold where sustained heat and drought make extreme wildfire a realistic possibility.

If the planet's warming is indeed lifting the flammability veil, as Swain describes it, the pressing question is whether communities everywhere are prepared for what lies beneath.

To contact the authors: Brian K. Sullivan in Boston at bsullivan10@bloomberg.net; Leslie Kaufman in New York at lkaufman27@bloomberg.net; Todd Woody in San Francisco at twoody4@bloomberg.net. This story was originally featured on Fortune.com.