Was common Era glacier expansion in the Arctic Atlantic region triggered by unforced atmospheric cooling?

The timing and causes of Common Era (CE) glacier growth in the Arctic Atlantic region remain elusive. There is mounting evidence of advances that predate the Little Ice Age (1250–1850 CE); this challenges the view that 13th century volcanic eruptions triggered change by spurring sea-ice expansion. Recent climate model simulations indicate this response does not require external forcing under contemporaneous (Pre-Industrial) boundary conditions. Here, we try to reconcile these new insights by combining regional proxy evidence of glacier and sea-ice change with a climate model experiment. Collated recently published reconstructions demonstrate that regional climate shifted towards a colder mean state around 650–950 CE, a period marked by low radiative forcing. Unforced model simulations reproduce the time-transgressive evolution of this response, which emerged east of Greenland and progressed towards Svalbard. The inferred pattern is associated with sea-ice feedbacks, triggered by stochastic atmospheric cooling. We argue that this mechanism may explain the timing and pattern of CE glacier growth in the region