Abstract
Mid-Holocene climate was characterized by strong summer solar heating that decreased Arctic sea ice cover. Motivated by recent studies identifying Arctic sea ice loss as a key driver of future climate change, we separate the influences of Arctic sea ice loss on mid-Holocene climate. By performing idealized climate model perturbation experiments, we show that Arctic sea ice loss causes zonally asymmetric surface temperature responses especially in winter: sea ice loss warms North America and the North Pacific, which would otherwise be much colder due to weaker winter insolation. In contrast, over East Asia, sea ice loss slightly decreases the temperature in early winter. These temperature responses are associated with the weakening of mid-high latitude westerlies and polar stratospheric warming. Sea ice loss also weakens the Atlantic meridional overturning circulation, although this weakening signal diminishes after 150–200 years of model integration. These results suggest that mid-Holocene climate changes should be interpreted in terms of both Arctic sea ice cover and insolation forcing.
Highlights
Mid-Holocene climate was characterized by strong summer solar heating that decreased Arctic sea ice cover
In our midHolocene simulation, Arctic sea ice concentration (SIC) in summer-autumn decreases by 30–35% over wide areas of the Arctic relative to the pre-industrial climate (Fig. 1), which is consistent with the multi-model averaged SIC anomalies in the mid-Holocene[11,12]
The longitude–time Hovmöller plot of surface air temperature (SAT) averaged between 45°N and 62°N (Fig. 2c) shows that the warming over the Pacific and North America persists throughout the season, whereas cooling over Central and East Asia appears in winter, especially in December and January
Summary
Mid-Holocene climate was characterized by strong summer solar heating that decreased Arctic sea ice cover. Over East Asia, sea ice loss slightly decreases the temperature in early winter These temperature responses are associated with the weakening of mid-high latitude westerlies and polar stratospheric warming. Sea ice loss weakens the Atlantic meridional overturning circulation, this weakening signal diminishes after 150–200 years of model integration These results suggest that midHolocene climate changes should be interpreted in terms of both Arctic sea ice cover and insolation forcing. Proxy data indicate that Arctic sea ice cover was smaller than the present during the mid-Holocene (around 6 ka BP) over Fram Strait, Baffin Bay, and the Labrador Sea[7] This is because summer insolation can warm the Arctic rapidly throughout the season, as sea ice decline can amplify the warming via various feedbacks, referred to as polar amplification[8,9,10]. The root-mean-square errors of sea ice extent and volume between CESM1–CAM5 and observations are one of the lowest[23] among 49 climate models that have participated in phase 5 of the Coupled Model Intercomparison Project (CMIP5)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
