Surprises for climate stability
By Thomas F. Stocker
Instabilities in Earth’s climate system have intrigued scientists ever since analyses from Greenland ice cores revealed climate variations over the last hundred thousand years (1, 2). Abrupt changes were not singular events but a pervasive feature of the last ice age. Studies pointed to the ocean, specifically the Atlantic Meridional Overturning Circulation (AMOC), as a possible origin of these large swings (3, 4). Their occurrence in the distant past of the last ice age and their absence in the past 8000 years suggested that we are living in times of relative climate stability. On page 1485 of this issue, Galaasen et al. (5) report that over the past 500,000 years, there were disruptions in the formation of the North Atlantic Deep Water mass—an essential driver of the AMOC—during interglacial periods. This suggests that substantial reductions or instabilities of the AMOC could also occur in a future warmer climate.