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.

北极永久冻土是地球冰冻圈最大的非季节性组成部分，包含大量对气候敏感的碳库。全球临界点是否存在，即一个变暖阈值，超过该阈值，永久冻土就会加速融化并自我延续，这一点仍然存在争议。在这里，我们对这个问题提供了一个综合的视角，表明尽管一些永久冻土融化反馈推动了局部到区域范围内的快速融化和不可逆转的地面冰损失，但北极永久冻土对气候变暖的累积反应仍然是准线性的。我们认为，在没有全球临界点的情况下，不存在可以接受的永久冻土损失的安全边际。相反，全球变暖的每一次加剧都会使更多永久冻土层下的土地面积融化，从而造成有害的局部影响和全球反馈。