For years scientists have been using biomarker evidence (IP25, PIP25) to reconstruct the Arctic’s sea ice history. The evidence shows modern (20th-21st century) Arctic sea ice is at its greatest extent since the Holocene began.
Scientists (Wu et al., 2020) have determined that from about 14,000 to 8,000 years ago, when CO2 lingered near 250 ppm, the Beaufort Sea (Arctic) was “nearly ice free throughout the year” (<0.2 PIP25) and ~4°C warmer than today in winter.
With CO2 at ~400 ppm, this region is 70-100% ice-covered (>0.8 PIP25) for all but 1-2 summer months in the modern (1988-2007) era.
Image Source: Wu et al., 2020
Interestingly, another study of this same Beaufort Sea region (Durantou et al., 2012) revealed the late 1800s to 1930s were up to 3°C warmer than the late 20th and early 21st century averages and sea ice was present for 1.1 fewer months per year during these earlier periods.
Image Source: Durantou et al., 2012
Another new study (Allaart et al., 2020) concludes that from around 10,000 to 5,000 years ago, Arctic Svalbard (Wijdefjorden) glaciers had retreated many km further back than their modern positions. And the smaller ice caps had “disappeared” from the region.
In contrast, during the last 500 to 700 years Svalbard sea ice has expanded to its highest extent of the Holocene (11,700 years ago to present).
The Holocene’s sea ice maximum just developed during modern times, as the authors note there has been an “increase in IP25 concentrations after c. 0.7±0.2 cal. ka BP, with a maximum in the modern sediments.”
Image Source: Allaart et al., 2020
A study site northeast of Svalbard (Brice et al., 2020) reveals today’s sea surface temperatures of “<0°C” are at least 4°C colder than they were just a few thousand years ago, when the Arctic was sea ice free for all but “a couple of months” every year.
Notice the graphics that show today’s sea ice monthly duration (~11 months per year) and summer sea surface temperatures (zero degrees Celsius) are among the highest and lowest (respectively) of the Holocene.
Image Source: Brice et al., 2020
October 29, 2020 at 09:57AM