Solar Forcing Of Modern, Historic Arctic Sea Ice Only Slightly Less Sea Ice Now Than Little Ice Age
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 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.
Robust substantiation for the trends documented in this new Arctic sea ice record comes from a 2005 paper by Lassen and Thejll entitled “Multi-decadal variation of the East Greenland Sea- Ice Extent: AD 1500-2000.” Shown below is an annotated graph from the paper revealing Iceland’s sea ice cover during the last millennium. These scientists also link sea ice variations to solar activity, namely solar cycle length. Notice the direct correspondence between the Arctic trends as a whole (from Stein et al., 2017) and the trends for Iceland.
The ’low frequency oscillation’ that dominated the ice export through the Fram Strait as well as the extension of the sea-ice in the Greenland Sea and Davis Strait in the twentieth century may therefore be regarded as part of a pattern that has existed through at least four centuries. The pattern is a natural feature, related to varying solar activity. The considerations of the impact of natural sources of variability on arctic ice extent are of relevance for concerns that the current withdrawal of ice may entirely be due to human activity. Apparently, a considerable fraction of the current withdrawal could be a natural occurrence.