Diverse terrestrial evidence for Holocene temperature trends over Greenland: a view from beyond the ice sheet

Reconstructing temperatures through the long-term, insolation-driven climate transitions of the Holocene is key to assessing Arctic system sensitivity to temperature change. Temperature reconstructions also provide key variables for data-model comparisons, including for studies used to evaluate ice sheet models. Yet until recently there have been few quantitative constraints on Holocene air temperatures over Greenland, especially the ice-marginal summer temperatures that drive ice sheet surface melt and many other impacts of climate change.

Our research group has applied diverse paleolimnological proxies to develop a network of temporally continuous Holocene temperature reconstructions from around Greenland. Paleoclimate proxies have included insect (chironomid) species assemblages, chironomid and sedimentary plant wax stable oxygen and hydrogen isotopes used to reconstruct stable isotopes of precipitation, and inferences of mountain glacier status. Here we summarize our findings alongside other published paleoecological, glacial geological and ice core-based evidence for Holocene temperatures across Greenland.

We find that peak summer warmth occurred in the earliest millennia of the Holocene in some sectors, including east-central and northwest Greenland. In contrast, peak warmth may have been delayed in southernmost Greenland. Peak warmth in the early Holocene is contrary to many climate model simulations, which show strong region-wide temperature depression from the residual Laurentide Ice Sheet. We also find that the maximum magnitude of multi-millennial cooling occurred in northwest Greenland, where summer cooling from the warmest millennium in the early Holocene to the pre-industrial last millennium probably exceeded 4 degrees C. Indeed, the reconstructed rate of overall Holocene cooling in most coastal sectors of Greenland exceeds published Arctic-wide average estimates, possibly because our estimates from Greenland are summer-biased. The magnitude of Holocene cooling inferred in some coastal sectors also exceeds that inferred from central Greenland ice cores. Southernmost Greenland may be an exception, where multi-millennial Holocene temperature changes were small even in summer; but conclusions from that region are preliminary as several key studies are ongoing.