It turns out back then Arctic insolation was bigger – although still a significant temperature response remained.
Eemian-Holocene sea level analogy
The analogy with the Eemian (just a bit warmer than today – a lot more water in the oceans) has been used to illustrate the possibility of larger sensitivity of the Greenland ice sheet to climate change, with perhaps several meters of sea level rise resulting from just a few degrees higher temperatures around the Arctic.
Early this year James Hansen co-wrote a paper that made a comparison with the Eemian to warn that perhaps the currently used climate and ice sheet models don’t reflect sensitivity to temperature rise good enough. Under the internationally agreed climate target of 2 degrees we may be in for multiple meters of sea level rise.
Milankovitch is all about solar radiation
We can’t resist to tell you we now feel a little bit clever as at the end of our article about that paper we suggested perhaps slight phase differences in the Milankovitch cycles could help explain the relatively large ice loss around the Arctic – as during summertime (when the albedo feedback is relevant) the incoming solar radiation could have been bigger then than it is now.
According to the Dutch researchers in their Nature Geoscience publication of Sunday Greenland contributed 2.2-4.5 meters to global sea level rise, corresponding with a 30-60 percent smaller ice sheet volume than today’s. During the period the insolation, so the amount of incoming solar radiation, was -on the northern hemisphere- larger than during the current interglacial, the Holocene.
The researchers have tuned a regional climate model to simulate Eemian conditions around the Greenland ice sheet. Together with ice feedbacks [like the albedo effect] creating a non-linear melting response, the researchers hold this solar influence responsible for 45 percent of the ice loss. The remaining 55 percent they contribute to a rise in ambient temperatures that they say was between 2-4 degrees – over Greenland that is.
Eemian comparison leftover 1: What about Antarctic insolation?
The Eemian comparison may however be more complex still. Another paleoclimatic study published in Science a little over a month ago suggests not Greenland was the main contributor to the Eemian sea level rise, but the West Antarctic ice sheet – suggesting the ice masses down south may not be as warming-resistent as we may think.
Eemian comparison leftover 2: How much is 55% of a lot?
And even under the most optimistic scenario, where southern hemisphere insolation was equally high during the Eemian and perhaps up to half of Antarctic melting was caused not by warming – the Eemian studies still show that multiple degrees of global average temperature rise will likely translate to multiple meters of sea level rise, which is more than we are generally prepared for – also because yet another Eemian study from last July, published in Geophysical Research Letters, states the mean Eemian sea level rise may have been higher – up to 8.5 meters.
What is perhaps most worrying: these scientists think this sea level rise should be linked to an average global temperature rise of just 0.7 degrees Celsius above current values. So don’t be too quick to say Hansen was wrong…
© Rolf Schuttenhelm | www.bitsofscience.org