Global Warming: Greenland losing ice seven times faster than the 1990s and will leave 40 million more people exposed to coastal flooding by 2100
Greenland's ice is shrinking faster than estimated, and it has lost 3.8 trillion tonnes of ice since 1992 — enough to push global sea levels up by 10.6 millimeters.
The rate of loss (image by Ian Joughin, University of Washington) has seen a seven-fold increase within three decades: rising from 33 billion tonnes each year in the 1990s to 254 billion tonnes each year in the last decade, according to a new analysis by 89 polar scientists.
The findings, says the research team from 50 international organizations, show that Greenland's ice losses are tracking the Intergovernmental Panel on Climate Change or IPCC's high-end climate warming scenario, which would see 40 million more people exposed to coastal flooding by 2100.
"This is a wake-up call — ice losses from Greenland are already tracking the worst-case scenario, and we have to believe they will continue to do so," Professor Andrew Shepherd at the University of Leeds tells MEA WorldWide (MEAWW).
He led the assessment along with Dr. Erik Ivins at the National Aeronautics and Space Administration or NASA's Jet Propulsion Laboratory in California.
(Ian Joughin, University of Washington)
According to Professor Shepherd, as a rule of thumb, for every centimeter rise in global sea level, another six million people are exposed to coastal flooding around the planet.
"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 the sea-level rise," says Professor Shepherd.
"Policymakers should plan for additional sea-level rise and to raise awareness of the coastal regions that will be affected by seasonal flooding in the future so that communities can be better prepared," he told MEAWW.
The Greenland Ice Sheet holds enough water to raise the mean global sea level by 7.4 meters. In recent decades, the Greenland Ice Sheet has been a significant contributor to global sea-level rise, and it is expected to be so in the future.
The IPCC predicts sea level will rise by 50 to 70 centimeters by 2100 under the recommended concentration pathway (RCP) 4.5, with a mid-range estimate of 60 centimeters. Greenland is expected to contribute 5 to 16 centimeters of this rise, with a mid-range estimate of 9 centimeters, says the study.
"In 2013, the IPCC predicted that global sea levels would rise by 60 centimeters by 2100, putting 360 million people at risk of annual coastal flooding.
But this new study shows that Greenland's ice losses are rising faster than expected and are instead tracking the IPCC's high-end climate warming scenario, which predicts 7 centimeters more," says the study published in Nature.
According to experts, 360 billion tonnes of ice is roughly equivalent to 1 millimeter of global sea-level rise.
The current study is an outcome of the Ice Sheet Mass Balance Inter-Comparison Exercise (IMBIE) supported by the European Space Agency (ESA) climate change initiative and the NASA cryosphere program.
The IMBIE team combined 26 separate surveys to compute changes in the mass of Greenland's ice sheet between 1992 and 2018. Data from 11 different satellite missions were used, including measurements of the ice sheet's changing volume, flow, and gravity.
The team also used regional climate models to show that half of the ice losses were due to surface melting as air temperatures have risen. The other half has been due to increased glacier flow, triggered by rising ocean temperatures.
According to the analysis, ice losses peaked at 335 billion tonnes per year in 2011 — 10 times the rate of the 1990s — during a period of intense surface melting.
The rate of ice loss dropped to an average of 238 billion tonnes per year since then, but this remains seven times higher and does not include all of 2019, which could set a new high due to widespread summer melting, say researchers.
"Satellite observations of polar ice are essential for monitoring and predicting how climate change could affect ice losses and sea-level rise. While computer simulation allows us to make projections from climate change scenarios, the satellite measurements provide prima facie, rather irrefutable evidence. Our project is a great example of the importance of international collaboration to tackle problems that are global in scale," says Dr. Ivins.
According to Guðfinna Aðalgeirsdóttir, professor of glaciology at the University of Iceland, who was not involved in the study, the current estimates of Greenland ice loss is timely for the IPCC.
"Their satellite observations show that both melting and ice discharge from Greenland have increased since observations started. The ice caps in Iceland had a similar reduction in ice loss in the last two years of their record, but this last summer was very warm here and resulted in a higher loss. I would expect a similar increase in Greenland mass loss for 2019," says Professor Aðalgeirsdóttir, who was the lead author of the IPCC's sixth assessment report.