Extreme Greenland ice melt increased global flood risk: Study

LONDON: Greenland has lost 3.5 trillion tonnes of ice over the past decade, increasing the global sea level by one centimetre and heightening the risk of flooding worldwide, according to a study published on Monday.

The international team of researchers made use of measurements from the European Space Agency (ESA)'s CryoSat-2 satellite mission, using estimates of surface elevation change over time.

The study, published in the journal Nature Communications, is the first to use satellite data to detect this phenomenon -- known as ice sheet runoff -- from space.

"Observations show that extreme melt events in Greenland have become more frequent and more intense -- as well as more erratic -- which is a global problem," said study co-author Lin Gilbert from University College London (UCL) in the UK.

"Monitoring from space enables us to cover the whole of Greenland (and nearly all Antarctica) repeatedly, which can't be done by teams on the ground," Gilbert said.

The researchers found that over the past four decades Greenland's meltwater runoff has risen by 21 per cent -- and has become 60 per cent more erratic from one summer to the next.

The study shows that between 2011 and 2020, increased meltwater runoff from Greenland raised the global sea level by one centimetre -- heightening the risk of flooding worldwide and disrupting marine ecosystems in the Arctic Ocean.

Rising sea levels can also alter patterns of ocean and atmospheric circulation that affect weather conditions across the globe, the researchers said.

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, they said.

The study shows that during the past decade, runoff from Greenland has averaged 357 billion tonnes of ice melt per year equating to almost one millimetre of global sea level rise.

This reached a maximum of 527 billion tonnes in 2012 when changes in atmospheric patterns caused unusually warm air to sit over much of the ice sheet, the researchers said.

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, they said.

"As we have seen with other parts of the world, Greenland is also vulnerable to an increase in extreme weather events," said study lead author Thomas Slater from the University of Leeds in the UK.

"As our climate warms, it's reasonable to expect that the instances of extreme melting in Greenland will happen more often -- observations such as these are an important step in helping us to improve climate models and better predict what will happen this century," Slater said.

The researchers noted 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.

The findings can also be used to verify how climate models simulate ice sheet melting, allowing improved predictions of how much Greenland will raise the global sea level in the future as extreme weather events become more common, they said.

"Model estimates suggest that the Greenland ice sheet will contribute between about 3-23 centimetres to global sea level rise by 2100," said study co-author Amber Leeson from Lancaster University, UK.

"This prediction has a wide range, in part because of uncertainties associated with simulating complex ice melt processes, including those associated with extreme weather," Leeson added.