Arctic Amplification: A Rapid Response to Radiative Forcing

Arctic amplification (AA) of surface warming is a prominent feature of anthropogenic climate change with important implications for human and natural systems. Despite its importance, the underlying causes of AA are not fully understood. Here, analyzing coupled climate model simulations, we show that AA develops rapidly (within the first few months) following an instantaneous quadrupling of atmospheric CO2. This rapid AA response-which occurs before any significant loss of Arctic sea ice-is produced by a positive lapse rate feedback over the Arctic. Sea ice loss is therefore not needed to produce polar-amplified warming, although it contributes significantly to this warming after the first few months. Our results provide new and compelling evidence that AA owes its existence, fundamentally, to fast atmospheric processes.