Europe’s Fire Threat and Permafrost Thaw: Beyond Climate Overshoot

The climate system does not always move backwards when temperatures do.

That matters because much of climate policy is built around the idea that temporary overshoot can eventually be corrected - emissions can fall, temperatures can stabilise, carbon can be removed from the atmosphere. But ecosystems have their own physical memory. A forest can burn faster than it can regenerate. Frozen soil can retain heat long after the atmosphere cools.

The question is no longer only how quickly humanity can stop warming. It is how much of the system will continue changing after that happens.

A fire can erase the forest that was there before

One of the clearest examples comes from a study of roughly 3,500 wildfires in Canada and the United States between 2012 and 2023.

Researchers from Western Colorado University, Colorado State University, the US Forest Service and other institutions analysed satellite data covering more than 33,000 days of fire activity. They compared how quickly fires moved through forests with how large and severe the resulting burns became.

The relationship was striking. The fastest-moving fires were not simply larger. They also tended to burn forests more severely.

Jonathan Coop, a professor at Western Colorado University and the study's lead author, said the most explosive fires could burn large areas at extremely high severity, changing the ecological conditions left behind.

That changes the meaning of a wildfire.

A forest destroyed by fire is not necessarily a forest waiting to grow back. In the most severely burned areas, the surviving trees that would normally provide seeds may be too far away. Large gaps appear in the landscape, and regeneration becomes difficult.

The result can be a different ecosystem altogether: another forest type, shrubs or grassland.

There is already evidence of what that can look like. Coop pointed to older Colorado fires, including parts of the area burned by the 2002 Hayman Fire, where he said there was effectively no prospect of the original ponderosa pine forest returning even after two decades.

“When we go into some of these slightly older burns, it really looks like there’s really no future for forests here,” he said.

That is an important distinction in the climate debate. Not every ecological change is necessarily a catastrophe. A grassland may be better adapted to a warmer and drier climate than the forest that occupied the same ground before.

But for people, the costs of such transitions can be substantial. Forest loss affects recreation and watershed health and can increase carbon emissions. It can also leave communities facing landscapes for which existing management practices were designed under conditions that no longer apply.

Coop is blunt about the limits of those tools. Prescribed burning and forest thinning can reduce fire severity, he said, but there are conditions under which megafires simply overwhelm what can be done on the ground.

“These fires have the fingerprints of climate change all over them,” he said.

That same problem is now appearing at a much larger European scale.

Europe is approaching the limits of fire management

A study led by the Potsdam Institute for Climate Impact Research projects that the area burned annually in Europe could increase by 39% by the end of the century even under a low-emissions pathway.

Under the high-emissions SSP3-7.0 scenario, the increase reaches 192% compared with the modelled 2000–2030 reference period.

The geography matters. At around 1.8°C of warming, fire activity is projected to rise across Europe. At roughly 3.6°C, the increase becomes particularly pronounced around the Mediterranean and across much of western and central Europe, including regions that have historically experienced fewer fires.

Maik Billing, the PIK researcher who led the study, said the results point to widespread increases in burned area even under comparatively low warming.

There is a second part to the research that is less fatalistic. Better prevention, detection and firefighting could significantly reduce the area burned. The modelling estimates that improved fire management could cut burned area by 92% in a 1.8°C future and by 72% at around 3.6°C.

But those figures come with a warning.

Thomas Hickler, a Senckenberg scientist and co-author, said Europe would need greater investment in trained crews, equipment and coordination. Yet he also cautioned that increasingly extreme fires could eventually exceed the ability of emergency services to contain them.

Recent fires in France illustrate the problem: experience is becoming a less reliable guide to the fires that responders will face.

Kirsten Thonicke of PIK put the strategic dilemma more directly. There may be a point at which local fire management simply reaches its limits.

The implication is not that prevention is futile. It is that adaptation has a ceiling.

Then there is what happens underground

The wildfire story becomes more consequential in the Arctic and sub-Arctic, where fire does not merely destroy vegetation.

It can remove the layer that keeps frozen ground cold.

Permafrost covers roughly 21mn sq km across the Northern Hemisphere. Its soils contain an estimated 1,100–1,500 gigatonnes of organic carbon accumulated over thousands of years.

The assumption that this carbon reservoir will respond neatly to changes in global temperature is now under pressure.

A Japanese study published in Earth System Dynamics on August 17 found that while the total area of permafrost can respond to warming and subsequent cooling, the deeper physical structure of the soil does not necessarily follow the same path.

The reason is basic physics. As frozen soil warms, some of its ice becomes water. When temperatures later fall, the deeper layers do not instantly return to their previous frozen state. Heat moves slowly through the ground, while the energy involved in changing water into ice creates another delay.

The ground therefore retains a memory of the warming episode.

In the researchers' modelling, this hysteresis generated additional carbon emissions during the cooling phase equivalent to between 0.6% and 41% of total carbon released from permafrost, depending on the scenario.

That range matters because it exposes a weakness in the idea of simply overshooting a temperature target and then correcting course.

The atmosphere may cool. The soil may not.

Fire removes the last layer of protection

Professor Gustaf Hugelius of Stockholm University has warned that heatwaves and wildfires are accelerating irreversible changes across the Northern Hemisphere's permafrost zone.

Fire is particularly damaging because the organic layer at the surface normally acts as insulation. Remove it, and summer heat can penetrate deeper into the ground, accelerating thaw.

That creates a feedback loop with no clean reset button. Warmer conditions contribute to more severe fires. Fires strip away insulation. Deeper thaw releases greenhouse gases. Those emissions add to warming.

Siberia is already providing evidence that this is not merely a theoretical chain.

Research covering 2010 to 2023 found that methane emissions in Siberia more than doubled over the decade, growing by about 5% a year. The increase was associated with rising surface temperatures, permafrost thaw and a sharp increase in boreal wildfires, particularly after 2019.

Methane is only part of the problem. Hugelius estimates that warming of 1.8°C to 3.6°C by 2100 could result in 200–300 gigatonnes of CO₂-equivalent emissions from permafrost.

He does not expect one global tipping point to arrive suddenly below 6°C of warming. The more plausible danger is a sequence of local tipping points, emerging in different regions as individual ecosystems lose their ability to recover.

That is a much harder problem for policy to manage.

A carbon budget can be adjusted. A burned forest and a thawed soil profile do not necessarily respond to policy on the same timetable.