Warming could itself trigger natural emissions capable of pushing global temperatures even higher.
To understand this mechanism, we need to look at what happens in certain environments as the planet warms. Permafrost thaws, fires burn more vegetation, and wetlands produce methane. These phenomena release carbon dioxide or methane, two gases that trap heat in the atmosphere.
Image: Jürgen Jester / Pixabay
The result forms a loop: human activities warm the climate, and that warming then causes new emissions. These, in turn, reinforce the rise in temperatures. An international team sought to estimate the combined effect of four major sources: permafrost, fires, wetlands, and inland waters such as lakes.
According to their calculations, these warming-driven emissions could increase the expected rise in temperatures over the course of the century by 20 to 30%. This would represent approximately 0.2 to 0.4 °C of additional warming by 2100, depending on how much greenhouse gas humanity continues to emit.
In a scenario where human emissions decline sharply, the additional effect would reach approximately 0.2 °C in 2100. In a scenario where they remain higher, it would approach 0.4 °C. However, the researchers give an uncertainty range of about 0.2 °C around these estimates.
Permafrost helps explain why the phenomenon can persist. These soils, frozen for a very long time, contain organic matter. When they thaw, microbes can break it down and release carbon dioxide or methane. The process therefore does not necessarily stop as soon as human emissions cease to increase.
Wetlands and lakes also respond to temperature. In some oxygen-poor environments, microbes produce more methane as conditions become warmer. Fires are another source: they rapidly release some of the carbon stored in vegetation and soils.
These phenomena have long been known, but their combined effect is still absent or incomplete in many climate projections.
Even after net human emissions reach zero, some of these natural sources could continue to act for decades. The authors therefore call for better integration of these sources into future climate models and calculations of the amount of carbon humanity can still emit to limit the rise in temperatures.