Rising temperatures are turning forests, wetlands, and tundra into additional sources of greenhouse gases. These emissions further heat up the planet and sustain a vicious cycle that could add between 0.2 and 0.4°C to global temperatures by the end of the century.
Emissions from natural processes triggered by warming could amplify by about 20–30% the temperature increase caused by human activity after 2020, as shown in a study published in the journal Environmental Research Letters.
The research, presented by The Guardian, analyzes the cumulative effect of four major sources: permafrost thawing, vegetation fires, wetlands, and inland waters such as lakes and rivers.
As the planet warms, organic matter frozen for thousands of years in permafrost begins to decompose, releasing carbon dioxide and methane. Warmer wetlands and lakes, in turn, produce more methane, while increasingly intense fires release into the atmosphere, in the form of carbon dioxide, some of the carbon stored in trees and soil.
The gases thus released further heat up the atmosphere, accelerating the processes that led to their release.
Warming could be greater than forecasts show
These natural emissions are not sufficiently accounted for in many climate forecasts. Consequently, temperature increases could be underestimated.
Depending on how quickly states reduce their emissions, the analyzed natural processes could add between 0.2 and 0.4°C to global warming by 2100. They could continue to warm the planet even after human emissions reach net zero levels.
"This hidden multiplier is missing from the models guiding climate policies," warned Sam Abernethy, the lead author of the study. According to him, forecasts could underestimate the future warming and overestimate the amount of carbon that humanity can still afford to emit.
Half of emissions could come from permafrost
Permafrost thawing could be responsible for approximately half of the additional emissions estimated by researchers.
Permafrost is soil that remains frozen for at least two consecutive years and contains very large amounts of organic matter and carbon. When it thaws, microorganisms break down this matter and release carbon dioxide and methane into the atmosphere.
"Warming-induced emissions have already begun and are increasing with every fraction of a degree. Any temperature increase we can avoid today matters for the long-term climate outlook," explained Christina Schädel, a researcher at the Woodwell Climate Research Center and co-author of the study.
Researchers emphasize that the results do not mean that a scenario of runaway warming is inevitable. The intensity of these natural reactions depends on the level of warming caused by humans.
The faster emissions from coal, oil, and gas burning are reduced, the lower the amount of greenhouse gases released later by permafrost, wetlands, lakes, and fires.
Every fraction of a degree matters
Current global policies would lead to a warming of about 2.6°C compared to the pre-industrial period, according to the Climate Action Tracker, an independent project monitoring government climate policies.
Such an increase would cause severe disruptions, from sea level rise and crop loss to heatwaves, droughts, and more severe floods. "One of the most worrying aspects of climate change is that warming can trigger natural processes that cause even more warming," explained Bill Ripple, an ecologist at Oregon State University who was not involved in the new research.
However, the study also shows that the magnitude of these processes can be limited. Rapid reduction of emissions from fossil fuels would temper the initial warming and, consequently, the natural reactions that amplify it.
G.P.