Ice flowed out of the interior of the Greenland ice sheet at much stronger rates and with much greater variability than today throughout the Holocene – or until about 2,000 years ago.
New research (Jansen et al., 2024) has determined Greenland’s ice streams vary according to internal processes, and not necessarily due to external changes in geothermal heat flux anomalies or climate.
These internally-variable ice stream patterns can change significantly in magnitude within time frames of just a few centuries, not the long-assumed 10,000- or 100,000-year time-spans.
This discovery of Greenland’s internally variable centennial-scale ice stream patterns should strongly impact modeled estimates of Greenland’s ice stream-based contributions to sea level rise, as it has long been assumed external factors (such as anthropogenic CO2 emissions) play an instrumental role in ice stream dynamics.
“Our results contradict the assumption that the ice stream has been stable throughout the Holocene in its current form, with distinct shear margins [ice flow volume changes] on time scales of hundreds of years, which is a major challenge for realistic mass-balance and sea-level rise projections.”
Image Source: Jansen et al., 2024
The authors of this new study had previously published a paper (Franke et al., 2022) suggesting highly variable Greenland ice streams “come and go” according to “spontaneous” processes that are still not fully understood.
Image Source: Franke et al., 2022
Relatedly, the ice melt at the interior of the Greenland ice sheet is flowing more slowly today than it has for 95% of the last 9,000 years – with the Little Ice Age the only period with less ice flow (MacGregor et al., 2016).
Image Source: MacGregor et al., 2016 and AAAS press release
Over the last millennium the volume of ice on the Greenland ice sheet has been much larger than it has been for the previous 9,000 years (Mikkelson et al., 2018).
Image Source: Mikkelson et al., 2018
When CO2 levels were in the mid-200s parts per million (11.7 to 4.5 thousand years ago) the Arctic and northern Greenland were 2-4°C warmer than now. Consequently, ice margins were 80 km behind today’s, ice-free open water conditions prevailed, and Greenland warmed 10°C in just 60 years (Elnegaard Hansen et al., 2022)
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