Nature Communications, 16 July 2026<\/p>\n
Temporarily exceeding global warming targets increases the risk of long-lasting changes to critical Earth systems, including the Atlantic Meridional Overturning Circulation (AMOC) and Arctic permafrost. The AMOC is a major system of Atlantic Ocean currents that carries heat northward. Warming and increased freshwater from melting ice can weaken this circulation, leading to regional cooling across parts of the Northern Hemisphere. At the same time, rising temperatures thaw permafrost, allowing microbes to decompose long-frozen organic matter and release carbon into the atmosphere, creating a self-reinforcing warming cycle. This is the first study to examine how these two processes interact. Using three climate models, the researchers found that cooling caused by a weakened AMOC can temporarily reduce permafrost thaw and lower carbon emissions from frozen soils. However, this cooling does not prevent continued permafrost carbon loss. Across all models, permafrost carbon emissions directly increase as warming increases, showing that both the magnitude and duration of warming determine how much carbon is irreversibly lost during overshoot. The findings reinforce that minimizing the peak temperature and length of any overshoot is essential to reduce the risks of triggering cascading changes across the Earth system.<\/p>\n