No respite from permafrost-thaw impacts in the absence of a global tipping point

Arctic permafrost, the largest non-seasonal component of Earth’s cryosphere, contains a substantial climate-sensitive carbon pool. The existence of a global tipping point, a warming threshold beyond which permafrost thaw would accelerate and become self-perpetuating, remains debated. Here we provide an integrative Perspective on this question, suggesting that despite several permafrost-thaw feedbacks driving rapid thaw and irreversible ground-ice loss at local to regional scales, the accumulated response of Arctic permafrost to climate warming remains quasilinear. We argue that in the absence of a global tipping point there is no safety margin within which permafrost loss would be acceptable. Instead, each increment of global warming subjects more land areas underlain by permafrost to thaw, causing detrimental local impacts and global feedbacks. It has been postulated that there is a threshold temperature above which permafrost will reach a global tipping point, causing accelerated thaw and global collapse. Here it is argued that permafrost-thaw feedbacks are dominated by local- to regional-scale processes, but this also means there is no safety margin.