Ice sheets in Antarctica and Greenland shrinking and melting since 2003 have contributed towards a global sea level rise, a NASA funded study revealed.
Researchers at the University of Washington examined data from two space lasers that were able to make the most precise measurements of the ice sheets to date.
They found the net loss of ice from Antarctica, along with Greenland’s shrinking ice sheet, has been responsible for 0.55 inches of sea level rise since 2003.
In Antarctica, sea level rise is driven by the loss of the floating ice shelves melting in a warming ocean – they hold back the flow of land-based ice into the ocean.
The study found that Greenland’s ice sheet lost an average of 200 gigatons of ice per year, and Antarctica’s ice sheet lost an average of 118 gigatons of ice per year.
One gigaton of ice is enough to fill 400,000 Olympic-sized swimming pools.
This shows the amount of ice gained or lost by Antarctica between 2003 and 2019. Dark reds and purples show large average rates of ice loss near the coasts, while blues show smaller rates of ice gain in the interior
The findings come from the Ice, Cloud and land Elevation Satellite 2 (ICESat-2), which was launched into orbit in the autumn of 2018.
The team behind the study compared recent ICESat-2 data to measurements from its predecessor taken between 2003 and 2009.
‘If you watch a glacier or ice sheet for a month, or a year, you’re not going to learn much about what the climate is doing to it,’ said lead author Benjamin Smith.
‘We now have a 16-year span between ICESat and ICESat-2 and can be much more confident that the changes we’re seeing in the ice have to do with the long-term changes in the climate,’ said the glaciologist at the University of Washington.
In Antarctica, sea level rise is driven by the loss of the floating ice shelves melting in a warming ocean – they hold back the flow of land-based ice into the ocean
‘We’re seeing high-quality measurements that carpet both ice sheets, which let us make a detailed and precise comparison with the ICESat data.’
Previous studies of ice loss or gain often analyse data from multiple satellites and airborne missions but the new study takes just a single type of measurement.
It takes height as measured by an instrument that bounces laser pulses off the ice surface – providing the most detailed and accurate picture of ice sheet change.
The researchers took elements of earlier ICESat measurements and overlaid the new data from ICESat-2 measurements taken last year.
They then ran the data through computer programs that accounted for the snow density and other factors, and then calculated the mass of ice lost or gained.
‘The new analysis reveals the ice sheets’ response to changes in climate with unprecedented detail, revealing clues as to why and how the ice sheets are reacting the way they are’, said co-author Alex Gardner, a NASA glaciologist
Of the sea level rise that resulted from ice sheet meltwater and iceberg calving, about two-thirds of it came Greenland, the other third from Antarctica
‘It was amazing to see how good the ICESat-2 data looked, right out of the gate,’ said co-author Tom Neumann, the ICESat-2 project scientist.
‘These first results looking at land ice confirm the consensus from other research groups, but they also let us look at the details of change in individual glaciers and ice shelves at the same time,’ Neumann said.
In Greenland, there was a significant amount of thinning of coastal glaciers.
The Kangerdulgssuaq and Jakobshavn glaciers, for example, have lost 14 to 20 feet of height per year for the past 16 years – the authors discovered.
Warmer summer temperatures have melted ice from the surface of the glaciers and ice sheets, and in some places warmer ocean water erodes away the ice at their fronts,’ the NASA backed team say.
In Antarctica measurements showed that the ice sheet is getting thicker in parts of the continent’s interior, likely as a result of increased snowfall, Smith said.
This shows the amount of ice gained or lost by Greenland between 2003 and 2019. Dark reds and purples show large rates of ice loss near the coasts. Blues show smaller rates of ice gain in the interior of the ice sheet
The loss of ice from the continent’s margins, especially in West Antarctica and the Antarctic Peninsula, far outweighs any gains in the interior.
‘In West Antarctica, we’re seeing a lot of glaciers thinning very rapidly,’ Smith said.
‘There are ice shelves at the downstream end of those glaciers, floating on water. And those ice shelves are thinning, letting more ice flow out into the ocean as the warmer water erodes the ice.’
These ice shelves, which rise and fall with the tides, can be difficult to measure, said co-author Helen Amanda Fricker, a glaciologist at Scripps Institution of Oceanography at the University of California, San Diego.
Some of them have rough surfaces, with crevasses and ridges, but the precision and high resolution of ICESat-2 allows researchers to measure overall changes, without worrying about these features skewing the results.
This is one of the first times that researchers have measured loss of the floating ice shelves around Antarctica simultaneously with loss of the continent’s ice sheet.
The study found that Greenland’s ice sheet lost an average of 200 gigatons of ice per year, and Antarctica’s ice sheet lost an average of 118 gigatons of ice per year
Ice that melts from ice shelves doesn’t raise sea levels, since it’s already floating – just like an ice cube in a full cup of water doesn’t overflow the glass.
But the ice shelves do provide stability for the glaciers and ice sheets behind them -‘It’s like an architectural buttress that holds up a cathedral,’ Fricker said.
‘If you take away the shelves, or even if you thin them, you’re reducing that buttressing force, so the grounded ice can flow faster.’
The researchers found ice shelves in West Antarctica, where many of the continent’s fastest-moving glaciers are located, are losing mass.
Patterns of thinning show that Thwaites and Crosson ice shelves have thinned the most, an average of about five meters (16 feet) and three meters (10 feet) of ice per year, respectively,’ the researchers said.
This NASA funded study has been published in the journal Science.