Greenland is losing ice seven times faster than in the 1990s and is tracking the Intergovernmental Panel on Climate Change’s high-end climate warming scenario, which would see 40 million more people exposed to coastal flooding by 2100.
A team of 96 polar scientists from 50 international organizations has produced the most complete picture of Greenland ice loss to date. The Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) Team combined 26 separate surveys to compute changes in the mass of Greenland’s ice sheet between 1992 and 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 on December 10, 2019 in Nature, (Shepherd, A., Ivins, E., Rignot, E. et al. “Mass balance of the Greenland Ice Sheet from 1992 to 2018”, Nature, 2019)
“Mass balance of the Greenland Ice Sheet from 1992 to 2018”) show that Greenland has lost 3.8 trillion tonnes of ice since 1992 – enough to push global sea levels up by 10.6 millimeters. The rate of ice loss has risen 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 Professor 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).
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.
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 tonnes 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 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.
Changes to the Greenland and Antarctic ice sheets are of considerable societal importance, as they directly impact global sea levels, which are a result of climate crisis. As glaciers and ice sheets melt, these add more water to the ocean.
IMBIE is an international collaboration between polar scientists from 50 scientific institutions supported by the European Space Agency and NASA.
The scientists-team found that half of the loss is tied to surface ice melting in warmer air. The rest of the loss is the result of factors such as warmer ocean temperatures, iceberg calving and the ice sheet shedding ice into the ocean more quickly.
Greenland is home to the only permanent ice sheet outside Antarctica. The sheet covers three-fourths of Greenland’s land mass. But in the last 26 years, Greenland’s melting ice has added 11 millimeters to sea level rise. Its cumulative 3.8 trillion tons of melted ice is equivalent to adding the water from 120 million Olympic-size swimming pools to the ocean every year, for 26 years.
“As a rule of thumb, for every centimeter rise in global sea level, another 6 million people are exposed to coastal flooding around the planet,” said Andrew Shepherd, lead author and scientist from the University of Leeds in the UK. “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 sea level rise.”
In addition to storm surges and high tides that will increase flooding in many regions, sea level rise exacerbates events like hurricanes. Greenland’s shrinking ice sheet also speeds up global warming. The vast expanse of snow and ice helps cool down Earth by reflecting the Sun’s rays back into space. As the ice melts and retreats, the region absorbs more solar radiation, which warms the planet.
The new study will contribute to the evaluation and evolution of sea level rise models used by the IPCC in evaluating risks to current and future populations. The results of the study currently appear consistent with the panel’s worst-case projections for sea level rise in the next 80 years.
This is the third IMBIE study on ice loss as a result of global warming. IMBIE’s first report in 2012 measured both Greenland and Antarctica’s shrinking ice sheets, finding that the combined ice losses from Antarctica and Greenland had increased over time and that the ice sheets were losing three times as much ice as they were in the early 1990s. Antarctica and Greenland continue to lose ice today, and that rate of loss has accelerated since the first IMBIE study.
Dr Ivins said: “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.”
Guðfinna Aðalgeirsdóttir, Professor of Glaciology at the University of Iceland and lead author of the IPCC’s sixth assessment report, who was not involved in the study, said:
“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.”
“It is very important to keep monitoring the big ice sheets to know how much they raise sea level every year.”
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