New findings on the past and future of sea ice cover in the Arctic

by Alfred Wegener Institute (AWI) on 30 Aug 2017 Despite the high temperatures, geologists and climate researchers find evidence that there was sea ice at the North Pole during the last interglacial. Temperatures in the Arctic are currently climbing two to three times faster than the global average. The result – and, thanks to feedback effects, also the cause – is dwindling sea ice. In a study published in the actual volume of Nature Communications, geo- and climate researchers at the Alfred-Wegener Institute, Helmholtz Centre for Polar- and Marine Research (AWI) show that, in the course of our planet’s history, summertime sea ice was to be found in the central Arctic in periods characterised by higher global temperatures – but less CO2 – than today.

Prognoses for the future of the Arctic can only be as reliable as the models and data they’re based on. The scenarios projected by climate modellers vary greatly, and it remains unclear when we can expect to see the Arctic Ocean free of ice in the summer. At the same time, there is considerable public interest in dependable predictions concerning Arctic sea ice development over the next few decades, so as to have a basis for long-term strategic planning.

Researchers at the Alfred Wegener Institute have now more closely analysed the glacial history of the central Arctic with the help of sediment core data and climate simulations. Their findings indicate that the region was home to sea ice during the last interglacial, between 115,000 and 130,000 years ago. “Thanks to the sediment core data, we have clear evidence that, during the last interglacial roughly 125,000 years ago, the central Arctic Ocean was still covered with sea ice during the summer. In contrast, in an area to the northeast of Spitsbergen, the summertime sea ice virtually disappeared,” explains Prof Rüdiger Stein, a geologist at the Alfred Wegener Institute and first author of the Nature Communications study, adding, “This is also confirmed by the climate simulations run by AWI modellers involved in the study.”

However, comparing the results of the climate simulations for the most recent interglacial with scenario calculations for the future reveals substantial differences: thanks to the more intense solar radiation, back then the air temperatures at higher latitudes were also a few degrees higher than at present. However, the carbon dioxide concentration in the atmosphere – roughly 290 ppm (parts per million) – was ca. 110 ppm lower than the current level, as ice core data from the Antarctic shows. For their scenario calculations, the AWI modellers plugged in atmospheric CO2 concentrations in excess of 500 ppm, a level in keeping with the forecasts released by the Intergovernmental Panel on Climate Change (IPCC).

Under these conditions, a disproportionately rapid retreat of summertime sea ice in the central Arctic Ocean over the course of the next few decades, followed by its complete disappearance – depending on how quickly CO2 levels rise – roughly 250 years from now, is to be expected. The outcomes of the study reveal the complexity of the processes shaping climate change in the Arctic and point to significant spatial and chronological variances in sea ice cover. To slow the warming of the Arctic and the permanent loss of sea ice, reducing the level of anthropogenic CO2 emissions in the atmosphere is vital.

Material published here and based on material from Ruediger Stein, Kirsten Fahl, Paul Gierz, Frank Niessen & Gerrit Lohmann: Arctic Ocean sea ice cover during the penultimate glacial and the last interglacial. Nature Communications. doi: 10.1038/s41467-017-00552-1