'Greater picture': Greenland ice losses faster than expected, say researchers
Researchers from Memorial University have joined a team of 96 polar scientists from 50 international organizations to produce the most complete picture of Greenland ice loss to date.
The Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) team, which includes Dr. Lev Tarasov, Department of Physics and Physical Oceanography, Faculty of Science, and his graduate student Benoit Lecavalier, combined 26 separate surveys to compute changes in the mass of Greenland’s ice sheet between 1992-2018.
Altogether, data from 11 different satellite missions were used, including measurements of the ice sheet’s changing volume, flow and gravity.
The findings, published Dec. 10 in the journal Nature, show that Greenland has lost 3.8 trillion tonnes of ice since 1992 – enough to push global sea levels up by 10.6 millimetres.
The rate of ice loss rose from 33 billion tonnes per year in the 1990s to 254 billion tonnes per year in the last decade – a seven-fold increase within three decades.
The assessment, led by Prof. Andrew Shepherd of the University of Leeds, and Dr. Erik Ivins of the United States National Aeronautics and Space Administration’s (NASA) Jet Propulsion Laboratory in California, was supported by the European Space Agency and NASA.
In 2013 the Intergovernmental Panel on Climate Change (IPCC) predicted that global sea levels will rise by 60 centimetres by 2100, putting 360 million people at risk of annual coastal flooding.
But this new study shows that Greenland’s ice losses rose faster than expected and are instead tracking the IPCC’s high-end climate warming scenario, which predicts seven centimetres more.
“As a rule of thumb, for every centimetre rise in global sea level, another six million people are exposed to coastal flooding around the planet,” said Prof. 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.”
Dr. Tarasov says, for various reasons, the models they use to predict future changes are more likely to under-predict than over-predict them.
“The results from this study are therefore more than likely a lower-bound estimate of sea-level rise contributions we can expect from Greenland,” he said. “To put the implications in perspective, consider the social-political disruption Europe has experienced in the last five years due to approximately three million migrants.
“Multiply this by 100 and impose a large fraction of this human displacement from rising sea level in the much poorer and politically stressed regions of Southeast Asia,” he continued. “This makes up part of my nightmare scenario for the world our children and grandchildren will be facing.”
The team also used regional climate models to show that half of the ice losses are due to surface melt as air temperatures rise.
The other half is been due to increased glacier flow, triggered by rising ocean temperatures.
Ice losses peaked at 335 billion tonnes per year in 2011 – 10 times the rate of the 1990s – during a period of intense surface melt.
Although the rate of ice loss dropped to an average 238 billion tonnes 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.
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,” said Dr. Ivins. “Our project is a great example of the importance of international collaboration to tackle problems that are global in scale.”
Mr. Lecavalier says his role in the project was to run computer simulations of the ice sheets, using data collected across Greenland to calibrate the models and make them accurately predict past ice-sheet changes.
“This gives us precious information about how the bedrock, the land under the ice, moves in non-uniform ways,” he said.
“At present, we still have residual movement that is occurring because of past changes, and those observations are needed to correct the satellite-made observations so we can confidently determine changes in the ice sheet.”
So, what does this all mean for the future of Newfoundland and Labrador?
“There could be a lot of real estate and infrastructure at risk.”
Mr. Lecavalier says what’s known as a 100-year, sea-level event – a high-water mark that the sea level reaches once every 100 years or so – may become more frequent, to the point where it might be occurring once a decade, or even once a year.
He says these occurrences “are not really factored in” to Newfoundland and Labrador’s infrastructure.
“Because of where our communities settled, there could be a lot of real estate and infrastructure at risk and may influence the relocation of communities by the end of the century because the cost of maintaining the infrastructure won’t make sense,” he said.
“The changing ocean temperatures will also affect ocean circulation and where fish live and spawn – the entire fisheries industry. That’s a completely separate matter from sea-level rise, but it’s all packaged into this greater picture of climate change.”