Greenland and Antarctica are losing 318 gigatons of ice each year

NASA scientists have used an advanced laser instrument to analyze changes in the Antarctic and Greenland ice sheets. The data shows how the ice sheets have changed over 16 years, including small gains in East Antarctica and massive losses in West Antarctica.

The experts found that overall ice losses from Antarctica and Greenland were responsible for 14 millimeters of sea level rise between 2003 and 2019. This is just under one-third of the total amount of sea level rise observed in the world’s oceans within this time period.

In 2018, NASA launched the Ice, Cloud and land Elevation Satellite 2 (ICESat-2) to make detailed global elevation measurements. The researchers compared data from ICESAT-2 with measurements taken by the original ICESat between 2003 and 2009 to produce a comprehensive portrait of ice sheet changes in Greenland and Antarctica.

According to the study, the Greenland ice sheet lost an average of 200 gigatons of ice per year and the Antarctic ice sheet lost an average of 118 gigatons of ice per year.

A single gigaton of ice is enough to cover New York’s Central Park in ice more than 1,000 feet thick, reaching higher than the Chrysler Building.

Study lead author Ben Smith is a glaciologist at the University of Washington.

“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 Smith, a and lead author of the new paper. “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.”

ICESat-2 measures land elevation using a laser altimeter that sends 10,000 pulses of light down to Earth’s surface per second. The instrument records the time it takes the light to return to the satellite to within a billionth of a second. 

To quantify how much ice has been lost, the researchers developed a new model which converts ice sheet volume to mass.

Tom Neumann is an ICESat-2 project scientist at NASA’s Goddard Space Flight Center.

“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,” said Neumann.

Detailed measurements in Antarctica showed that the ice sheet is getting thicker in parts of the continent’s interior as a result of increased snowfall. However, a warming ocean has caused ice losses in West Antarctica and the Antarctic Peninsula that outweigh any gains in the interior.

Smith said there was a significant amount of thinning of coastal glaciers in Greenland. For example, the Kangerlussuaq and Jakobshavn glaciers have lost 14 to 20 feet of elevation per year. Hotter temperatures in the summer have melted ice from the surface of the glaciers and ice sheets, while the warmer ocean water has eroded away the front of the ice in some basins.

Study co-author Alex Gardner is a glaciologist at NASA’s Jet Propulsion Laboratory in Southern California.

“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 Gardner. 

Ice melt from the shelves does not raise sea levels because it is already floating. However, the ice shelves are needed to keep the glaciers and ice sheets behind them stable.

Study co-author Helen Amanda Fricker is a glaciologist at Scripps Institution of Oceanography at the University of California San Diego.

“It’s like an architectural buttress that holds up a cathedral. The ice shelves hold the ice sheet up,” explained Fricker. “If you take away the ice shelves, or even if you thin them, you’re reducing that buttressing force, so the grounded ice can flow faster.”

The study is published in the journal Science.

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By Chrissy Sexton, Earth.com Staff Writer