Wildfires feel more frequent and destructive because several forces are converging at once: hotter, drier conditions are priming landscapes to burn, humans are starting the vast majority of fires, decades of fire suppression have loaded forests with excess fuel, and millions more homes now sit in fire-prone areas. The total area burned globally has actually declined over the past century, largely due to the conversion of grasslands and savannas to farmland. But in forested regions, especially across North America, fires are burning hotter, lasting longer, and causing far more damage than they did a generation ago.
Humans Start Most Wildfires
In the United States, people cause 84% of all wildfires. Lightning accounts for the rest. That statistic comes from an analysis of 1.5 million fires, and the implications go beyond just the number of ignitions. Human-caused fires have tripled the length of the fire season compared to what lightning alone would produce, and they dominate an area seven times larger than the zone affected by lightning fires. They’re also responsible for nearly half of all acreage burned.
The reason is simple: people start fires in places and at times of year that lightning does not. Power lines, campfires, discarded cigarettes, equipment sparks, and arson all introduce ignition sources into landscapes that wouldn’t otherwise burn during those months. This stretches the window of fire risk well beyond the traditional summer thunderstorm season.
Hotter, Drier Air Makes Fuel Ready to Burn
Climate plays a central role, and the mechanism is straightforward. As temperatures rise, the atmosphere pulls more moisture out of vegetation and soil. Scientists track this through a measure called vapor pressure deficit, which captures how dry the air is relative to how much moisture it could hold. The drier the air, the faster dead leaves, branches, and even living plants lose their moisture. Once that fuel dries out, it ignites more easily and burns more intensely.
Vapor pressure deficit has been rising in the western United States and strongly correlates with the amount of land that burns each year. It affects both dead material on the forest floor (which responds quickly to weather) and living vegetation (which can dry out and die during prolonged drought, adding even more fuel). The result is that when a fire does start, it encounters a landscape primed to carry flames fast and far.
Fire seasons are also getting longer. Parts of the western U.S., Mexico, Brazil, and East Africa now face wildfire seasons more than a month longer than they were 35 years ago, based on a NASA analysis of meteorological data spanning from 1979 to 2013.
A Century of Fire Suppression Built Up Fuel
For most of the 20th century, the U.S. and other nations treated all wildfire as an enemy to be extinguished immediately. That policy succeeded at putting out small fires but created a long-term problem. Many forests, particularly in the American West, evolved with frequent, low-intensity fires that cleared out underbrush and thinned smaller trees every few years or decades. When those fires were systematically suppressed, dead wood, dense brush, and young trees accumulated on the forest floor for generations.
The U.S. Forest Service now acknowledges that this approach drastically altered historic fire patterns, leading to excessive fuel buildup and “uncharacteristically severe wildfires” when fires do break through suppression efforts. In some areas, forests also shifted toward more fire-sensitive tree species that burn more readily. The fires that escape today aren’t just bigger; they burn through fuel loads that wouldn’t have existed under natural fire cycles.
More People Live Where Fires Burn
The wildland-urban interface, where homes and communities meet undeveloped land, is the fastest-growing land use type in the contiguous United States. Between 1990 and 2010, the number of houses in this zone grew from 30.8 million to 43.4 million, a 41% increase. The land area classified as wildland-urban interface expanded by 33%, from 581,000 to 770,000 square kilometers. By 2010, roughly one in three American homes sat in this fire-prone border zone.
This growth directly increases wildfire damage even when fire behavior itself hasn’t changed. Within the perimeters of wildfires that burned between 1990 and 2015, there were 286,000 houses standing in 2010, compared to 177,000 in 1990. More structures in the path of fire means more destruction, higher suppression costs, and more dramatic headlines, all of which contribute to the perception that fires are worse than ever.
Suppression Costs Keep Climbing
Federal wildfire suppression spending in the U.S. tells its own story. In 2014, the combined spending by the Forest Service and Department of the Interior was about $1.5 billion. By 2018, it had more than doubled to $3.1 billion. The year 2021 set a record at $4.4 billion. Even in 2023, a relatively modest fire year by acreage (2.7 million acres burned), suppression still cost $3.2 billion.
These rising costs reflect not just more fire but more expensive fire. Protecting homes and infrastructure in the wildland-urban interface requires heavy aerial resources, large firefighting crews, and extended deployments. A fire burning through remote wilderness costs a fraction of what it takes to defend a subdivision at the edge of a forest.
Northern Forests Are Burning Differently
Boreal forests across Alaska and Canada are experiencing a shift in fire behavior. The interval between fires in the same area is shrinking, with short-interval burns (less than 20 years between fires) becoming more common over time. Historically, these northern forests might go 80 to 200 years between burns, giving them time to regrow thick organic soil layers and store enormous amounts of carbon.
The 2023 Canadian fire season showed what this new pattern looks like at scale. More than seven times the average annual area burned compared to the previous four decades, and the fires released an estimated 647 teragrams of carbon, comparable to the annual fossil fuel emissions of a large industrialized nation. That year was also the warmest and driest in Canada since at least 1980, illustrating how heat, drought, and fire feed on each other in these ecosystems.
Prescribed Fire Helps, but Fades Quickly
One of the most effective tools for reducing wildfire severity is prescribed burning, where land managers intentionally set controlled fires to reduce fuel loads. Research from the southeastern U.S. confirms that wildfire severity is generally lower in areas that have been treated with prescribed fire. The greatest benefit shows up in the wildland-urban interface, where reducing fuel around communities directly protects homes.
The catch is that the benefit doesn’t last. Burn severity in treated areas creeps back up over time as new vegetation grows in and dead material accumulates again. This means prescribed fire needs to be repeated on a regular cycle to remain effective, and current treatment rates fall far short of what’s needed. The U.S. treats a few million acres per year with prescribed fire, while tens of millions of acres carry dangerous fuel loads.
Global Area Burned Is Actually Declining
Here’s the counterintuitive part: the total area burned by fire worldwide has been decreasing, dropping roughly 2% per year between 2003 and 2012. There is strong evidence that less land burns today than at any point in the past several centuries. The reason is primarily agricultural expansion. Grasslands and savannas in Africa, South America, and Asia that once burned regularly have been converted to cropland, removing them from the fire cycle entirely.
This global decline masks what’s happening in forested regions. While grass fires in sub-Saharan Africa are down, forest fires in North America, Siberia, and the Mediterranean are burning with greater intensity and causing outsized damage. The fires making international news aren’t grassland burns in rural Africa. They’re high-severity forest fires destroying communities, blanketing cities in smoke, and releasing centuries of stored carbon in a matter of days. So while the planet as a whole has less fire, the fires we do have are concentrated in the places and ecosystems where they cause the most harm.