Cooling threshold
The end of each interglacial period over the past 800,000 years was characterized by large, abrupt cooling episodes that were distinct from the gradual decrease in insolation that was occurring. Why did these sudden coolings occur? Yin et al. used a suite of climate models to show that an insolation threshold exists, beneath which the slow decrease of energy from the Sun leads to rapid climate cooling. This effect results from weakening of the Atlantic meridional overturning circulation involving sea ice feedbacks in the Nordic and Labrador Seas.
Science, abg1737, this issue p. 1035
Abstract
Abrupt cooling is observed at the end of interglacials in many paleoclimate records, but the mechanism responsible remains unclear. Using model simulations, we demonstrate that there exists a threshold in the level of astronomically induced insolation below which abrupt changes at the end of interglacials of the past 800,000 years occur. When decreasing insolation reaches the critical value, it triggers a strong, abrupt weakening of the Atlantic meridional overturning circulation and a cooler mean climate state accompanied by high-amplitude variations lasting for several thousand years. The mechanism involves sea ice feedbacks in the Nordic and Labrador Seas. The ubiquity of this threshold suggests its fundamental role in terminating the warm climate conditions at the end of interglacials.
