Amplified warming risks from long-term climate and carbon feedbacks

Berlin, Germany (SPX) Mar 25, 2025
Global temperatures could rise more than previously projected due to persistent feedback mechanisms between the climate system and the carbon cycle, according to new research from the Potsdam Institute for Climate Impact Research (PIK). This study, which is the first to forecast climate change over the next 1,000 years while accounting for established carbon cycle feedbacks such as methane emissions, reveals that the goal of keeping warming well below 2oC, as set by the Paris Agreement, may only be possible under very low emissions pathways and if climate sensitivity is at the lower end of current scientific estimates.

"Our study demonstrates that even in emission scenarios typically considered 'safe', where global warming is generally considered to remain below 2oC, climate and carbon cycle feedbacks, like the thawing of permafrost, could lead to temperature increases substantially above this threshold," said PIK scientist Christine Kaufhold, lead author of the paper published in Environmental Research Letters.

She noted that the research shows significantly higher peak warming than earlier estimates under low-to-moderate emissions conditions. This suggests that relatively small variations in emissions may cause much greater warming than anticipated, making it increasingly difficult to achieve the Paris climate goals. "This highlights the urgent need for even faster carbon reduction and removal efforts," Kaufhold explained.

The study differs from many existing analyses by extending projections far beyond the 21st century, with most studies ending in 2100 or 2300. By utilizing longer simulation periods and including major carbon feedbacks such as the methane cycle, researchers could estimate the extent of additional warming and identify possible temperature peaks.

Using PIK's Earth system model CLIMBER-X, the team simulated climate outcomes over a millennium across three low-to-moderate emissions scenarios that reflect ongoing decarbonization trends. This model integrates essential physical, biological, and geochemical processes, including atmospheric and oceanic dynamics. Crucially, it features an interactive carbon cycle, incorporating methane, to model how Earth responds to different greenhouse gas concentrations driven by human activities.

Climate sensitivity, a pivotal factor in climate projections, also played a central role in the study. Simulations explored equilibrium climate sensitivity (ECS) values ranging from 2oC to 5oC, a spectrum deemed "very likely" by the Intergovernmental Panel on Climate Change. ECS represents the anticipated global temperature rise from a doubling of atmospheric CO2.

"Our results show that the Paris Agreement's goal is only achievable under very low emission scenarios and if the ECS is lower than current best estimates of 3oC," stated PIK scientist Matteo Willeit, a co-author of the study. "If the ECS exceeds 3oC, carbon reduction must accelerate even more quickly than previously thought to keep the Paris target within reach." The findings emphasize how critical ECS is in determining future climate patterns and the risks associated with uncertainties in its estimation. The authors underscore the need for improved accuracy in calculating ECS.

"Our research makes it unmistakably clear: today's actions will determine the future of life on this planet for centuries to come," concluded PIK director Johan Rockstrom, also a co-author. "The window for limiting global warming to below 2oC is rapidly closing. We are already seeing signs that the Earth system is losing resilience, which may trigger feedbacks that increase climate sensitivity, accelerate warming and increase deviations from predicted trends. To secure a liveable future, we must urgently step up our efforts to reduce emissions. The Paris Agreement's goal is not just a political target, it is a fundamental physical limit."

Research Report:Interplay between climate and carbon cycle feedbacks could substantially enhance future warming