// ARS TECHNICA — FINANZA
How the world’s fires changed while humanity hit pause
COVID-19 lockdowns cut global fire activity by 12.3 percent.
Wildfires occur worldwide, and they can sometimes become serious threats to people’s lives. A series of massive bushfires from 2019 to 2020 swept across southeastern Australia and destroyed thousands of homes. Recently, the 2025 Los Angeles wildfires spread widely across the city, resulting in massive damage to local communities.
Many things can cause wildfires, but humans are the only factor that can also make preventative efforts. Measuring people’s impact on fire is difficult because of the mix of human and natural influences.
A team led by Jianghao Wang, a professor at the Chinese Academy of Sciences, recently published a study in Cell Reports Sustainability comparing the COVID-19 era with other years. Data from the 2020 lockdowns suggest that lower human activity at this time had the net effect of lowering average fire activity.
Fire doesn’t just happen anywhere. Although plenty of flammable materials exist in natural settings, not every place experiences wildfires. Some prairies burn almost every year, while many forests go without big fires for hundreds of years. Researchers explain these differences in terms of fire regimes, which are patterns describing when, how often, and how widely and intensely fires occur.
Weather is a major factor affecting fire regimes. An abundance of rain helps grow grass and trees that can become fuel for fires. Whether they do or not, however, can depend on the moisture inside plants; plants with enough moisture do not burn easily. By contrast, dry conditions make them more likely to catch fire. When a drought lasts, vegetation becomes increasingly flammable. Strong winds also accelerate fire growth and spread enormously.
Human activity often combines with weather conditions to cause fires. Even routine outdoor recreation can accidentally start a fire. More people venture outdoors during sunny, drier times of the year, increasing the risk of accidental fires when dry vegetation is more likely to be present.
The double-sided role of humans in fire also adds to the difficulty. Humans do start fires, but they also put them out. Firefighters contain fires that could have gone worse if no action had been taken and can keep them from spreading. Humans can also take preventative actions, such as clearing flammable material.
Sometimes the line between starting fires and preventing them becomes blurred. One way to clear out flammable material is to intentionally set fires to make future fires more manageable. However, these fires are hard to distinguish from other fires through satellite monitoring.
An experiment is one way to find out how humans affect wildfires. If everyone stayed home under the same weather, their impact on fires would be revealed. This is why Wang’s research team focused on the COVID-19 era. It was what’s called a “natural experiment,” in which experimental conditions arose without any action by researchers.