Warming of Northern Peatlands Increases the Global Temperature Overshoot Challenge

To meet the Paris Agreement temperature goal, allowable carbon emissions in the future are tightly limited. It is very likely that the 1.5°C temperature limit will be at least temporarily exceeded (overshoot) under an emission pathway following current climate policies and actions. Peatlands store large amounts of soil carbon, the destabilization of which could potentially cause large amplifying feedback on global warming. Using the reduced-complexity Earth system model OSCAR v3.1.2 and a new peat carbon module, we assessed whether carbon emissions from northern peatlands triggered by climate change will increase the chance and intensity of temperature overshoot. We found that, although northern peatlands continue to accumulate carbon, they represent positive feedback under climate change through their high CH₄ emissions. For a 1°C increase in peak temperature anomaly, emissions from peatlands further contribute to the peak temperature by 0.02 (0.01-0.02) °C. Considering northern peatlands would lead to a reduction in the carbon budget by about 40 (16-60) GtCO₂, or 8.6% for 1.5°C, and a reduction of about 105 (45-166) GtCO₂ reduction (or 4.2% relative decrease) for 2.5°C. Our findings highlight the importance of properly accounting for northern peatland emissions for estimating climate feedbacks, especially under overshoot scenarios.