Melting ice melts more ice

In February 2019, Nick Golledge and his collaborators published two new papers in the journal Nature (February 2019, vol 566).

Patterns of changes in ice-sheet thickness by 2100 compared to 2000 in Antarctica and Greenland
Patterns of changes in ice-sheet thickness by 2100 compared to 2000 in Antarctica and Greenland

The first of these, led by Nick and bringing together a team of climate and ice sheet modellers from New Zealand, the UK, Canada, the USA and Germany, presented results from simulations of the Greenland and Antarctic ice sheets under low and high greenhouse gas emissions scenarios forecast for the 21st century. The culmination of three year’s work, the model experiments used observational data to constrain all parts of the mass budget of the two ice sheets. That is, the models correctly simulated the balance between accumulation, calving of icebergs, and melting of floating ice. By also running climate model experiments in which ice sheet melt influenced oceanic conditions, Nick and his team explored a positive feedback effect that previous work had suggested could lead to accelerated ice sheet retreat. Nick’s results showed that this feedback could almost double the amount of ice loss, substantially alter ocean circulation, and disrupt global climate. But the results also predicted less sea level rise by 2100 than some previous studies.

In the second paper, Tamsin Edwards (King’s College London) and Nick used a statistical approach to reassess one such study, showing that the mechanisms previously invoked were not actually necessary for explaining past, or present, ice loss. Without those mechanisms the predicted sea level contribution from Antarctica reduces considerably. Despite this ‘good news’, the models also predicted that even under a mitigated emissions scenario and immediate stabilization of global climate, parts of West Antarctica will still most likely collapse. Since this process of self-sustaining retreat has already been initiated, our best hope to limit the scale and speed of this retreat is to implement rapid and widespread emissions reductions, across the world.

For more information contact: Nick Golledge