Warming Triggers Emissions That Most Climate Models Miss

Greenhouse gases released by warming itself could add 0.2 to 0.4 °C to global temperatures by 2100, according to a projection published Sept. 10 in Environmental Research Letters by Sam Abernethy and Benjamin Poulter of Spark Climate Solutions and eight colleagues.

The emissions are natural rather than industrial: permafrost, wetlands, fresh waters and wildfire release more greenhouse gases as the planet heats. Most climate models do not yet include that response. This absence "risks systematic underestimation of projected future warming and overestimation of remaining carbon budgets."

The team worked out how emission rates rise with global temperature, using process-based models, which simulate each source directly, across three standard emissions scenarios spanning deep cuts to continued high emissions. For each additional °C of warming, the four sources together release about 97 million metric tons of methane a year. Permafrost and wildfire alone add about 7 billion metric tons of carbon dioxide a year per degree, in the two higher-emissions scenarios.

Fed into MAGICC, a climate model that turns emission paths into temperatures, those rates produce the added warming, split roughly equally between carbon dioxide and methane. The added warming amplifies human-caused warming after 2020 by 20% to 30%, with a combined uncertainty of plus or minus 0.2 °C.

The study is open access under a CC BY 4.0 license. Its authors work at Spark Climate Solutions, the Woodwell Climate Research Center, the Environmental Defense Fund and Stanford University.