The collapse of Northern Hemisphere ice sheets has been deemed as a trigger of positive climate feedback during Quaternary glacial terminations. Increasing boreal summer insolation is widely considered the primary driver; however, the precise initiating mechanisms remain elusive. Here we report an unambiguous warming trend in the southern Nordic Seas since the late Last Glacial Maximum, coinciding with the marked increase in 65°N summer insolation, and subsequently followed by a distinct surface cooling linked to intense freshwater discharge. Our reconstructions indicate that the initial collapse during the Last Termination began within the Eurasian Ice Sheet. Increasing boreal insolation weakened the latitudinal insolation gradient and displaced the westerlies northward, promoting poleward oceanic heat transport and ensuing warming in the Nordic Seas. This warming accelerated the disintegration of marine-terminating glaciers of the Eurasian Ice Sheet, leading to a catastrophic meltwater release. The resulting freshwater perturbation contributed to the early weakening of the Atlantic Meridional Overturning Circulation and ultimately triggered the destabilization of the Laurentide Ice Sheet, further accelerating the deglaciation process. Rising boreal insolation enhanced poleward heat transport and Nordic Seas warming since the late LGM, triggering the initial Eurasian Ice Sheet collapse. The resulting meltwater led to early AMOC weakening and acceleration of the deglaciation process.
Wu et al. (2026) studied this question.