Increased global flood risk due to intense frequency of extreme ice melting in Greenland

Surface meltwater flowing in Greenland

Surface melt water flows towards the sea through a canal in Greenland. Credit: Ian Joughin

Global warming has caused extreme ice melting events in Greenland to become more frequent and more intense over the last 40 years, according to new research, which has raised sea levels and the risk of floods worldwide.

Over the past decade alone, 3.5 trillion tons of ice have melted from the surface of the island and flowed downhill into the ocean.

It is enough melted ice to cover the whole of Britain with about 15 meters of meltwater, or cover the entire city of New York by about 4500 meters.

The new study, led by the University of Leeds, is the first to use satellite data to detect this phenomenon – known as ice runoff – from space.

The results, published in Nature communication, reveal that Greenland’s meltwater runoff has increased by 21% over the past four decades and has become 60% more irregular from one summer to the next.

Main author Dr. Thomas Slater, a research fellow at the Center for Polar Observation and Modeling at the University of Leeds, said:

“As we have seen with other parts of the world, Greenland is also vulnerable to an increase in extreme weather events.

“As our climate warms, it is reasonable to expect that cases of extreme meltdown in Greenland will occur more frequently – observations such as these are an important step in helping us improve climate models and better predict what will happen in this century. “

The study, funded by the European Space Agency’s (ESA) as part of the Polar + Surface Mass Balance Feasibility project, used measurements from ESA’s CryoSat-2 satellite mission.

Research shows that over the past decade (2011 to 2020), increased runoff of meltwater from Greenland has raised global sea levels by one centimeter. One third of this total was produced in just two hot summers (2012 and 2019), where extreme weather led to record levels of ice melting that have not been seen in the last 40 years.

Elevated sea levels caused by melting ice increase the risk of flooding for coastal communities worldwide and disrupt marine ecosystems in the Arctic Ocean on which indigenous communities depend for food.

It can also change patterns of the ocean and atmospheric circulation, which affect weather conditions around the planet.

Over the past decade, runoff from Greenland has averaged 357 billion tonnes per year, reaching a maximum of 527 billion tonnes of ice melt in 2012, when changes in atmospheric patterns caused unusually warm air to sit over much of the ice sheet. This was more than double the minimum runoff of 247 billion tonnes that occurred in 2017.

The changes are related to extreme weather events, such as heat waves, which have become more frequent and are now a major cause of ice loss from Greenland due to the runoff they produce.

Dr. Slater said: “However, there are reasons to be optimistic. We know that setting and meeting meaningful targets to reduce emissions can reduce the ice loss from Greenland by a factor of three, and there is still time to achieve this.”

These initial observations of Greenland’s runoff from space can also be used to verify how climate models simulate the melting of the ice cap, which in turn will allow improved predictions of how much Greenland will raise global sea levels in the future as extreme weather events become more common.

The study’s co-author Dr. Amber Leeson, associate professor of environmental data science at Lancaster University, said:

“Model estimates indicate that the Greenland ice sheet will contribute between about 3 and 23 cm to the global sea level rise in 2100.

“This prediction has a wide range, in part due to uncertainties associated with simulating complex ice melting processes, including those associated with extreme weather. These new space-borne estimates of runoff will help us better understand these complex ice melting processes, improve our ability to model them and thus enable us to refine our estimates of future sea level rise. “

Finally, the study shows that satellites are able to provide immediate estimates of this summer’s ice melt, which supports efforts to expand Greenland’s hydropower capacity and Europe’s ambition to launch the CRISTAL mission to succeed CryoSat-2.

ESA’s CryoSat mission manager, Tommaso Parrinello, said:

“Since its launch over 11 years ago, CryoSat has provided a wealth of information about our rapidly changing polar regions. This remarkable satellite remains the key to scientific research and the indisputable facts such as these results on meltwater runoff that are so crucial for decision making about the health of our planet.

As we look further into the future, the Copernicus Sentinel Expansion Mission CRISTAL will ensure that the Earth’s vulnerable ice will be monitored for decades to come. In the meantime, it is imperative that CryoSat remains in orbit for as long as possible in order to reduce the gap before these new Copernicus missions become operational. “

Reference: “Increased variability in Greenland Ice Sheet runoff from satellite observations” by Thomas Slater, Andrew Shepherd, Malcolm McMillan, Amber Leeson, Lin Gilbert, Alan Muir, Peter Kuipers Munneke, Brice Noël, Xavier Fettweis, Michiel van den Broeke and Kate Briggs November 1, 2021, Nature communication.
DOI: 10.1038 / s41467-021-26229-4

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