Forest fires are burning nearly twice as much tree cover today compared to two decades ago, with climate change driving increasingly severe fire weather conditions that are transforming forests into tinderboxes across the globe.
New data covering 2001 to 2023 reveals that forest fires now consume nearly 6 million more hectares of tree cover annually than they did in 2001 — an area roughly the size of Croatia. The area burned by forest fires has increased by about 5.4 percent each year over that period, according to researchers at the University of Maryland whose findings were published by the World Resources Institute.
Climate change has emerged as the primary driver behind this escalation, creating fire-favorable weather conditions that allow blazes to ignite more easily, spread faster, and burn more intensely than ever before. The warming atmosphere is essentially becoming thirstier, pulling moisture from vegetation and soil at unprecedented rates.
The Science Behind the Surge
A key factor in understanding this phenomenon is vapor pressure deficit, a measure of how much moisture the atmosphere can absorb. As temperatures rise due to climate change, the air’s capacity to hold water vapor increases exponentially, creating a powerful drying effect on forests and grasslands.
Research published in the Proceedings of the National Academy of Sciences found that warming temperatures contributed to 80 percent of the vapor pressure deficit increase across the western United States between 1979 and 2020. Scientists determined that 68 percent of this increase resulted from human-caused global warming, with only 32 percent attributed to natural climate variability.
“The leading cause of the rapid increase of wildfires over the western U.S. is the rapid increase of surface air vapor pressure deficit, or VPD, a measure of how thirsty the atmosphere is,” according to the study funded by NOAA’s Climate Program Office.
This atmospheric thirst has dramatic consequences for forests. When vapor pressure deficit rises, trees and other vegetation lose water more rapidly, creating drier fuel loads that ignite more easily and burn more fiercely. The process creates a feedback loop where climate change makes fires more likely, and those fires release greenhouse gases that accelerate warming.
Global Fire Patterns Shift
The increase in fire activity varies significantly by region, with some of the most dramatic changes occurring in areas where fires were historically less common. Boreal forests in northern Canada and Russia have experienced particularly severe increases, with fire-related tree cover loss rising by about 138,000 hectares per year over the past 23 years.
“The Canadian Interagency Forest Fire Centre reports that an estimated 9.5 million hectares of land was burned between January and July 2023, an area equivalent to the size of Portugal.” This trend is especially concerning because boreal forests store 30 to 40 percent of all terrestrial carbon globally.
Even tropical forests, where fires are not part of the natural ecosystem, are experiencing unprecedented burning. Fire-related tree cover loss in tropical regions increased at a rate of about 41,500 hectares per year between 2001 and 2023, with much of this driven by deforestation that makes remaining forests more vulnerable to burning.
2024 Sets New Records
The year 2024 marked a catastrophic milestone, with global forest loss reaching unprecedented levels. For the first time since record-keeping began, fires rather than agriculture became the leading cause of tropical primary forest loss, accounting for nearly 50 percent of all destruction.
The fires of 2024 released 4.1 gigatons of greenhouse gas emissions globally — more than four times the emissions from all air travel in 2023. Brazil alone saw a sixfold increase in fire-related primary forest loss compared to 2023, fueled by the worst drought on record.
Longer, More Intense Fire Seasons
Climate change has fundamentally altered the timing and duration of fire seasons around the world. Research shows the wildfire season has lengthened in many areas due to warmer springs, longer summer dry seasons, and drier soils and vegetation. In Alberta, Canada, the fire season now begins a full month earlier than it used to, starting in March rather than April.
The National Oceanic and Atmospheric Administration found that climate change has been the main driver of increased fire weather in the western United States, with drought and persistent heat creating extraordinary wildfire seasons from 2020 to 2022.
Western fire managers report that fires are burning longer throughout the day and into the night compared to previous decades. Nighttime vapor pressure deficits have increased by more than 50 percent over 40 years in the foothills of the Sierra Nevada and Rocky Mountains, meaning fires that once died down overnight now maintain their intensity.
Projections Point to Smokier Future
Scientists project that fire conditions will continue to deteriorate as the planet warms. Research indicates that for much of the western United States, an average annual 1-degree Celsius temperature increase would increase the median burned area per year by as much as 600 percent in some types of forests.
Models suggest that with continued high emissions of greenhouse gases, the risk of very large wildfires could increase by up to six-fold in parts of the United States by mid-century. Global fire carbon emissions from forest regions increased by 60 percent between 2001 and 2023, and this trend appears likely to accelerate.
Fire researcher Mike Flannigan, who has studied wildfire for over thirty years, doesn’t mince words about what lies ahead. When asked about climate change’s impact on wildfires in Canada, he responds simply: “in a word, the future is smoky.”
Managing the Crisis
While the outlook appears daunting, scientists and fire managers emphasize that adaptation strategies can help reduce risks. These include prescribed burning to reduce fuel loads, creating defensible space around communities, improving forest management practices, and investing in early detection and rapid response systems.
However, researchers stress that addressing the root cause — greenhouse gas emissions from fossil fuels — remains essential for limiting future fire risks. The Global Forest Watch notes that protecting forests from deforestation and degradation also improves their resilience to fire.
As extreme fire weather becomes more common and severe, communities worldwide face the urgent challenge of adapting to a reality where forests that once rarely burned now regularly burst into flames, threatening lives, property, and the global climate system itself.
