The urgency to combat global warming just got augmented by research published in the journal Nature Communications last week, reiterating that 2021 is one of the biggest ice melt years in history for Greenland, home to the biggest ice sheet in the world behind Antarctica. The Greenland ice sheet has melted so much in the past decade that global sea levels rose by 1cm, and trends predict sea levels can rise nearly a foot higher by the end of the century. The Greenland melt events are heightening the risk of flooding worldwide and disrupting marine ecosystems in the Arctic Ocean. Raising sea levels can also alter patterns of ocean and atmospheric circulation that affect weather conditions across the globe.
An ice sheet is a mass of glacial land ice extending more than 50,000sq km. The two ice sheets on Earth today cover most of Greenland and Antarctica. During the last ice age, ice sheets also covered much of North America and Scandinavia. Together, the Antarctic and Greenland ice sheets contain more than 99% of the freshwater ice on Earth. The Antarctic ice sheet extends almost 14mn sq km, roughly the area of the contiguous US and Mexico combined. The Antarctic ice sheet contains 30mn cubic km of ice. The Greenland ice sheet extends about 1.7mn sq km, covering most of the island of Greenland, three times the size of Texas.
Global warming has caused extreme ice melting events in Greenland to become more frequent and intense over the past 40 years, finds the new research involving University College London (UCL) academics. Greenland’s meltwater has risen by 21% — and has become 60% more erratic from one summer to the next. Over the past decade alone, 3.5tn tonnes of ice has melted from Greenland’s surface and flowed into the ocean — enough to cover the UK with around 15m of meltwater. One third of this rise was produced in just two summers — 2012 and 2019 — when extreme weather led to record-breaking levels of ice melting not seen in the past 40 years.
The study shows that during the past decade, runoff from Greenland has averaged 357bn tonnes of ice melt per year — equating to almost 1mm of global sea level rise — reaching a maximum of 527bn tonnes in 2012, when changes in atmospheric patterns caused unusually warm air to sit over much the ice sheet. These changes are related to extreme weather events such as heatwaves, which have become more frequent and are now a major cause of ice loss from Greenland.
The new study is the first to use satellite data to detect this phenomenon — known as ice sheet runoff — from space. Funded by the European Space Agency (ESA) as part of its project ‘Polar+ Surface Mass Balance Feasibility’, the study used measurements from the ESA’s CryoSat-2 satellite mission, using estimates of surface elevation change over time. One of the very few satellites orbiting with 2 degrees of the planet’s poles, CryoSat-2 has provided scientists with a long history of data no other spacecraft could reach since its launch over 11 years ago, transforming scientist’s capacity to study the polar regions. It remains key to research and knowledge critical to decision-making on the planet’s health.
As lead author Dr Thomas Slater (University of Leeds) said there are, however, reasons to be optimistic. “We know that setting and meeting meaningful targets to cut emissions could reduce ice losses from Greenland by a factor of three, and there is still time to achieve this.” That is some relief.
