Photo: NASA Earth Observatory

North in flames: Satellite image of a large-scale fire in western Greenland.

The Arctic is not only snow and ice. Peat layers and the vegetation of the tundra and taiga provide abundant highly flammable fuel. Since the early 2000s, the extent and frequency of major fires in the Arctic have increased markedly. The years 2019, 2020 and 2021 represent a preliminary peak: in just three years, more area burned north of the 60th parallel than in the entire decade from 1990 to 2000.

Lukas Fiedler systematically investigated, as part of his doctoral research, how strongly human-caused climate change is fueling these fires. The doctoral researcher at the Earth and Society Research Hub (ESRAH) at the University of Hamburg conducted the research together with colleagues from the Max Planck Institute for Meteorology.

The result: human-caused emissions are a necessary condition for the occurrence of these extreme events. This is particularly evident in so-called fire weather—climatic conditions that determine how easily fires can ignite and spread. For 2020 and 2021, the human influence is close to one hundred percent. “An event like 2021 becomes 235 times more likely due to human-caused climate change,” Fiedler says. “The clarity of these numbers surprised even me.”

Human influence is also detectable in the size of the burned area, albeit less sharply—because additional local factors such as potential ignition sources or vegetation also play a role.

Using climate simulations, the team compared how likely the extreme fires are in a world with human influence and how likely they are in a world without it. The researchers then broke down the drivers of fire danger into their individual components. This allowed them to show that it is not a lack of rainfall, but rising temperatures and increasingly dry air that are the decisive drivers of Arctic extreme fires.

For a long time, the Arctic was considered a carbon sink, binding more CO₂ than it releases. However, recent record fires in Siberia and Canada have already released more than one billion tonnes of carbon—comparable to the annual emissions of a major industrialized country. If the Arctic tips from CO₂ store to CO₂ source, it could make climate mitigation efforts worldwide more difficult. “Instinctively, you know extremes are getting worse,” Fiedler says. “With our analysis, we can now demonstrate what humans are actually causing.”

Publication: Attribution of observed pan-Arctic extreme fire events to anthropogenic forcings