New Study: More Arctic Sea Ice Now Than For Nearly All Of The Last 10,000 Years
In a new paper (Stein et al., 2017), scientists find that Arctic sea ice retreat and advance is modulated by variations in solar activity. In addition, the sea ice cover during the last century has only slightly retreated from the extent reached during coldest centuries of the Little Ice Age (1600s to 1800s AD), which had the highest sea ice cover of the last 10,000 years and flirted with excursions into year-round sea ice.
The Medieval Warm Period sea ice record (~900 to 1200 AD) had the lowest coverage since the Roman era ~2,000 years ago.
Of note, the paper makes no reference to carbon dioxide or anthropogenic forcing as factors modulating Arctic sea ice.
The causes that are controlling the decrease in sea ice are still under discussion. In several studies changes in extent, thickness and drift of Arctic sea ice are related to changes in the overall atmospheric circulation patterns as reflected in the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO). The NAO and AO are influencing changes of the relative position and strength of the two major surface-current systems of the Arctic Ocean.
The increase in sea ice extent during the late Holocene seems to be a circum-Arctic phenomenon, coinciding with major glacier advances on Franz Josef Land, Spitsbergen and Scandinavia. The increase in sea ice may have resulted from the continuing cooling trend due to decreased solar insolation and reduced heat flow from the Pacific.
The increase in sea ice extent during the late Holocene seems to be a circum-Arctic phenomenon as PIP25-based sea ice records from the Fram Strait, Laptev Sea, East Siberian Sea and Chukchi Sea display a generally quite similar evolution, all coinciding with the decrease in solar radiation.
The main factors controlling the millennial variability in sea ice and surface-water productivity are probably changes in surface water and heat flow from the Pacific into the Arctic Ocean as well as the long-term decrease in summer insolation, whereas short-term centennial variability observed in the high-resolution middle Holocene record was possibly triggered by solar forcing.