What’s all the talk about melting ice and rising sea levels?

Flow of ice into seas is speeding up due to climate change, three new studies show

Penny Ice Cap outlet glacier on Baffin Island which shows ‘rivers’ of ice as they flow towards the sea. Photograph: Michael Studinger/Nasa

What’s with all the talk about ice melting at the poles and rising sea levels? Is there something new going on?

It all has to do with melting glaciers and rising sea levels due to climate change, as described in a cluster of recent scientific reports .

The amount of ice flowing into the oceans from Greenland and Antarctica is increasing as warming water near the poles eats away at the feet of massive glaciers. Some of these glaciers have gone into "irreversible retreat" according to researchers who say this could push up sea levels by more than a metre.

The Antarctic and Greenland ice sheets lock up more fresh water than there is on the rest of the planet combined but the flow of ice into seas is speeding up due to climate change, according to research reports published within the past 10 days by Geophysical Research Letters , Nature Geoscience and Science.


How does it happen?

The processes involved are threatening massive glaciers, rivers of ice that flow off the land and into the sea. These glaciers rest on bedrock well below sea level and they usually flow very slowly because of their massive weight.

But our oceans are heating up due to global warming and this is having an effect on the glaciers. Last week scientists from the University of California, Irvine and Nasa's Jet Propulsion Laboratory in Pasadena reported in Geophyiscal Research Letters that six huge West Antarctic glaciers were being eaten away from below by warming sea waters.

What difference does that make?

If the restraining foundations are lost or weakened the ice can flow much faster and these six had “gone into a state of irreversible retreat”, said lead author Eric Rignot of Irvine. The Thwaites, Pine Island, Haynes, Pope, Smith and Kohler glaciers hold enough water to raise sea levels by 1.2 metres, with the Thwaites alone accounting for half of this.

A separate research report by the University of Washington in the journal Science also reported the Thwaites as being in an unstoppable collapse. What makes it worse is the fact that the Thwaites "also acts as a linchpin on the rest of the ice sheet which contains enough ice to cause another three to four metres of sea level rise", their report said.

Is that what is happening in Greeland?

The warming seas are chewing away at the base of glaciers on the fringes of Greenland, according to the Nature Geoscience report, but there is something extra going on there. The scientists used radar to look at the bedrock buried beneath the ice and found that there were long deep valleys that reach back under the ice for tens of kilometres and sometimes more than 100km.

The bases of these grounded glaciers lie under sea level, allowing warmer oceans to flow up along these valleys and undermine the glaciers for dozens of kilometres inland, loosening their foundations and causing faster ice flow from land.

These reports mirror earlier work that indicates that the massive ice sheets of Greenland and West Antarctica are far more vulnerable that realised. The Irvine researchers clocked the ice flow from the West Antarctic ice sheet over the period 1992-2011. They found the Smith/Kohler glaciers were in the fastest retreat of 34 to 37km over the 20 year period.

Dick Ahlstrom

Dick Ahlstrom

Dick Ahlstrom, a contributor to The Irish Times, is the newspaper's former Science Editor.