Eemian sea level rise update: just 1.6-2.2m from Greenland – Antarctic ice sheet less stable than we think?

Last week we learned 5 percent of the Eemian sea level rise was thermal expansion of the oceans. Today we learn the slightly higher temperatures led Greenland to ‘only’ add an extra 1.6-2.2m. Do we fail to spot the Antarctic Achilles’ heel?

A group of scientists from the University of Wisconsin and Oregon State University have researched silt sediments around Greenland dating back to the Eemian, some 130,000-114,000 years ago, and predecessor to our current interglacial period, the Holocene.

Greenland Ice Sheet reconstruction

From this they can reconstruct glacier extent. The biggest part of the Greenland Ice Sheet actually survived the relatively warm [just 0.7 degrees Celsius warmer than the Holocene] period, it turns out.

From the ice surface the researchers have also reconstructed the ice volume. What went missing went into the sea: Greenland meltwater contributed 1.6-2.2 meters to the Eemian sea level rise, they write in today’s Science.

Antarctic instability

This means – to climatologists’ slight surprise – melting of the Antarctic ice sheets likely contributed the majority of the Eemian sea level rise. Just what percentage is however unclear. We know the average sea levels of the Eemian were several meters higher than today’s. What isn’t helping is the fact that different studies use very different figures, ranging from 4 meters, to 8.5 meters.

We can anyway conclude that our vision of Antarctica as that isolated deep freeze bastion may require reconsideration. Somehow the ice can respond dramatically to slight warming.

Sea level feedback speculation

Perhaps geology provides a clue. If you look at the map – beneath the ice – you see two large dents, covered by the Ronne Ice Shelf and the Ross Ice Shelf, just west of the Transantarctic Mountain range and separating the West Antartic Ice Sheet from the East Antarctic Ice Sheet.

Although both areas are close to the actual South Pole and should therefore be able to withstand some warming, there may be another factor that could destabilise the ice: sea level rise. Would the 1.6-2.2 meters of Greenland meltwater be enough to drive a wedge of water under the Ronne and Ross ice, uncorking other West Antarctic ice masses?

We don’t want to pretend any cleverness. It’s just that we recently learned not all positive climate feedbacks require warming. And we don’t make these things up ourselves.