|Prof. Brian Gunter|
A group of more than 90 international scientists -- including AE professor Brian Gunter - has released findings that indicate Greenland's ice loss between 1992 and 2018 is enough to push sea levels up by 10.6 millimeters.
The Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) Team used data from 11 different satellite missions - including measurements of the ice sheet’s changing volume, flow and gravity - to complete its report, which was summarized recently in the journal Nature.
The group found that Greenland's rate of ice had increased seven fold - from 33 billion tons per year in the 1990’s to 254 billion tons per year in the last decade. Overall, they estimated that Greenland had shed 3.8 trillion tons of ice over the 26-year period.
The assessment, led by Prof. Andrew Shepherd at the University of Leeds and Dr Erik Ivins at NASA’s Jet Propulsion Laboratory in California, was supported by the European Space Agency (ESA) and the US National Aeronautics and Space Administration (NASA).
"The study synthesized its findings by taking estimates of the Greenland ice mass change from across the globe. These were derived from satellite remote sensing and other data sets from leading research groups," said Gunter, who also contributed to a 2018 study that revealed similar trends in Antarctica.
"My group contributed one of the 26 different estimates used in the study. We derived our data from altimetry measurements from NASA’s Ice, Cloud and Land Elevation (ICESat-1) mission. The study is important because it showed an overall consensus in the results that Greenland has been losing a substantial amount of ice over the past two decades, which has implications to our understanding and response to climate change."
In 2013, the Intergovernmental Panel on Climate Change (IPCC) predicted that global sea levels will 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.
“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," said Shepherd.
“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.These are not unlikely events or small impacts; they are happening and will be devastating for coastal communities.”
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.
Ice losses peaked at 335 billion tons per year in 2011 – ten times the rate of the 1990s - during a period of intense surface melting. Although the rate of ice loss dropped to an average 238 billion tons per year since then, this remains seven times higher and does not include all of 2019, which could set a new high due to widespread summer melting.
“Our project is a great example of the importance of international collaboration to tackle problems that are global in scale," said Ivins. "While computer simulation allows us to make projections from climate change scenarios, the satellite measurements provide prima facie, rather irrefutable, evidence. Satellite observations of polar ice are essential for monitoring and predicting how climate change could affect ice losses and sea level rise”.
Though not involved in this particular study, Prof. Guðfinna Aðalgeirsdóttir -- the lead author of the Intergovernmental Panel on Climate Change’s sixth assessment report -- applauded the Greenland group for monitoring the ice sheet and sea level changes.
“The IMBIE Team’s reconciled estimate 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 similar reduction in ice loss in the last two years of their record, but this last summer was very warm here and resulted in higher loss. I would expect a similar increase in Greenland mass loss for 2019.”
Read the Nature article on the Greenland study
Read the Nature article on the Antarctica study