Around 200,000 yr ago, Homo sapiens emerged in Africa. By 40 ka, Homo sapiens had spread throughout Eurasia, and a major competing species, the Neanderthals, became extinct. The factors that drove our species "out of Africa" remain a topic of vigorous debate. Existing research invokes climate change as either providing opportunities or imposing limits on human migration. Yet the paleoclimate history of northeast Africa, the gateway to migration, is unknown. Here, we reconstruct temperature and aridity in the Horn of Africa region spanning the past 200,000 yr. Our data suggest that warm and wet conditions from 120,000 to 90,000 yr ago could have facilitated early waves of human migration toward the Levant and Arabia, as supported by fossil and lithic evidence. However, the primary out-of-Africa event, as constrained by genetic studies (ca. 65-55 ka), occurred during a cold and dry time. This complicates the climatemigration relationship, suggesting that both "push" and "pull" factors may have prompted Homo sapiens to colonize Eurasia.

The middle to late Holocene (8,200 years ago to present) in the Arctic is characterized by cooling temperatures and the regrowth and advance of glaciers. Whether this Neoglaciation was a threshold response to linear cooling, or was driven by a regional or Arctic‐wide acceleration of cooling, is unknown. Here we examine the largest‐yet‐compiled multiproxy database of Arctic Holocene temperature change, along with model simulations, to investigate regional and Arctic‐wide increases in cooling rate, the synchronicity of Neoglacial onset, and the observed and simulated rates of temperature change. We find little support for an Arctic‐wide onset of Neoglacial cooling but do find intervals when regions experienced rapid increases in long‐term cooling rate, both in the observations and in climate model simulations. In the model experiments, Neoglacial cooling is associated with indirectly forced millennial‐scale variability in meridional heat transport superposed on the long‐term decline of summer insolation.

Marked changes in sediment types deposited in Cabin Lake, near Cordova, Alaska, represent environmental shifts during the early and late Holocene, including fluctuations in the terminal position of Sheridan Glacier. Cabin Lake is situated to receive meltwater during periods when the outwash plain of the advancing Sheridan Glacier had aggraded. A brief early Holocene advance from 11.2 to 11.0 cal ka is represented by glacial rock flour near the base of the sediment core. Non-glacial lake conditions were restored for about 1000 years before the water level in Cabin Lake lowered and the core site became a fen. The fen indicates drier-than-present conditions leading up to the Holocene thermal maximum. An unconformity spanning 5400 years during the mid-Holocene is overlain by peat until 1110 CE when meltwater from Sheridan Glacier returned to the basin.