Climate Models Miss a Set of Feedback Loops, and We May Have Underestimated Global Warming by 0.4°C

James Temple notes in the report published by MIT Technology Review that the models behind UN climate reports have omitted a set of amplifying warming effects.

Rising temperatures trigger further warming. Thawing permafrost releases carbon dioxide and methane, wildfires burn carbon stored in forests and soil back into the atmosphere, and hotter lakes, reservoirs and warmer, wetter wetlands are also driving higher emissions. These processes are called feedback loops. Scientists have long warned of their risks, but only until recent observations and research have their impacts been quantified with specific figures.

A comprehensive study published in Environmental Research Letters in September compiled results from multiple previous papers. It concludes that the extra carbon dioxide and methane released solely from thawing permafrost, intensifying wildfires, heating lakes and reservoirs, and warming and wetting wetlands could push the global average temperature up by another 0.2°C to 0.4°C this century, on top of existing projections. Under current emission paths, models estimate the global temperature will be around 2.6°C higher than the pre-industrial level by 2100. That extra amount of warming is enough to leave many cities under heatwaves lasting for months, and expose hundreds of millions of people to flood risks.

The problem is that the models that form the basis for major UN climate reports do not fully account for all these feedback effects. Many of them do not factor in even one of these processes. This leaves a huge blind spot: we may have severely underestimated how much the Earth will actually warm in the coming decades, as well as how quickly countries need to cut their emissions.

An analysis published in One Earth in March offers more specific calculations. It only assessed three regional sources: thawing permafrost, rising boreal forest fires, and warming tropical wetlands. These three factors alone could shorten the timeline for the world to permanently break through the 1.5°C and 2°C warming thresholds by up to 25%. Sam Abernethy, the lead author of the paper and a climate scientist at Spark Climate Solutions, argues that models and UN reports need to be updated, and countries' emission reduction efforts should be adjusted accordingly.

Scientists are already working to fill this gap. Spark has launched a project called the Warming-Induced Greenhouse Gas Emissions Model Intercomparison Project, in which more than 20 international teams run the same set of analyses with different models, to figure out exactly how strong these feedback effects are. Participants hope the next major UN climate assessment, due to be released in 2029, will incorporate these results. That report will update a key estimate: how much more carbon the world can emit before crossing critical temperature thresholds.

Some research teams have begun to explore the possibility of directly suppressing these feedback-driven emissions. The Woodwell Climate Research Center in Massachusetts is studying fire prevention methods, or rapid detection and extinguishing of fires that threaten permafrost, which locks away huge amounts of carbon that wildfires can release by destroying its insulating layer. The Environmental Defense Fund's Climate Innovation Initiative is funding laboratory research that attempts to add sulfates, iron or other compounds to wetlands to suppress the rapidly rising methane emissions. Startups are also looking at more radical solutions: suppressing more frequent lightning-induced fires in high-latitude regions, laying synthetic mats over permafrost, and using autonomous drones to quickly put out fires that could generate high emissions.

These ideas are worth studying. But given the massive scale and drastic, fast changes of global ecosystems, the exact emission reduction effect of any such intervention is still in the very early stage of assessment. When the model baseline is set too low, policy discussions will be overly lenient. Conversely, when feedback effects are fully accounted for, emission reduction targets will clearly need to be much stricter.

The most reliable path remains the old, proven answer: breaking society's dependence on fossil fuels. It may sound nothing new, but the more feedback effects models miss, the more impossible it becomes to avoid this essential transition.