Both the scale and speed of Greenland’s ice losses are much higher than predicted, according to a new paper published on 10 December in Nature (1). The authors claim ice loss today is occurring seven times faster than in the 1990s, tracking high-end warming predictions of the Intergovernmental Panel on Climate Change (IPCC), and could place an additional 40 million people are at risk of coastal flooding by 2100.
The Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) team, an international scientific collaboration between 96 polar scientists from 50 international organisations, compiled data on the mass of Greenland’s ice sheet between 1992 and 2018 from 11 different satellite missions, including changes in ice sheet volume and flow.
The study was led by Prof Andrew Shepherd at the University of Leeds and Dr Erik Ivins of NASA’s Jet Propulsion Laboratory in California and supported by the European Space Agency (ESA) and the US National Aeronautics and Space Administration (NASA).
The scientists discovered that since 1993, Greenland has lost 3.8 trillion tonnes of ice. Even more worrying, the rate of ice losses has increased from 33 billion tonnes per year in the early 1990s to 254 billion tonnes per year in the last decade — In other words, ice loss has nearly doubled every decade.
The researchers also used regional climate models to show that roughly half of the ice loss was due to warmer temperatures, which have risen much faster in the Arctic compared to the global average, and caused significant surface melting of the ice sheet. The other main contributor to ice losses was warming ocean temperatures, which triggered glacier ice flow.
Moreover, unlike floating sea ice that makes up most of the Arctic ice cap, Greenland’s ice sheet rests on a large landmass and therefore, melting contributes directly to sea-level rises. According to the authors, the total ice loss between 1992 and 2018 equated to around one centimetre of global sea-level rise.
Although this might not sound like much, “as a rule of thumb, for every centimetre rise in global sea level another six million people are exposed to coastal flooding around the planet”, explains Shepherd. Therefore, “on current trends, Greenland ice melting will cause 100 million people to be flooded each year by the end of the century, so 400 million in total due to all sea-level rise”.
Greenland’s ice loss is accelerating much faster than the IPCC predictions published in 2013, and is more in line with high-end warming scenarios, which Shepherd warns could be “devastating for coastal communities”. Indeed, many experts worry IPCC predictions do not take into account the potential for tipping points that could lead to catastrophic and irreversible changes.
Ice loss peaked in 2011 during a period of intense surface melting — at a rate 10 times higher than in the 1990s — and since dropped to 238 billion tonnes per year, on average. But this is still seven times higher than the early 1990s. And the data does not include 2019, which saw unprecedented summer temperatures in Europe and elsewhere.
The IMBIE report is timely as governments meet for the second week of the UN climate summit in Madrid, Spain to discuss the climate emergency. The findings provide yet more evidence that real and immediate action is needed to prevent the potentially devastating effects of climate change.
(1) The IMBIE Team. Mass balance of the Greenland Ice Sheet from 1992 to 2018. Nature (2019). DOI: 10.1038/s41586-019-1855-2