NASA space laser missions map ice sheet loss in 16 years

James Marshall
May 3, 2020

The net ice mass loss has led to nearly half an inch of sea-level rise between 2003 and 2019 - just under a third of the total sea-level rise around the world in that time.

The study found each year, Greenland lost an average of 200 billion tonnes of ice and Antarctica lost an average of 118 billion tonnes.

The researchers used the elevation measurements from both satellites to determine how Antarctica's mass balance - the difference between accumulation and loss - changed from 2003 to 2019 for each of its 27 drainage basins. By comparing the recent data with measurements taken by the original ICESat from 2003 to 2009, researchers have generated a comprehensive portrait of the complexities of ice sheet change and insights about the future of Greenland and Antarctica. The satellite's laser altimeter sends 10,000 pulses of light down to Earth's surface every second, and times how long it takes for the reflected pulses to come back. Here, Ben Smith and colleagues aggregated 2018 and 2019 data from ICESat-2 to 2003 to 2008 data from ICESat. That could be an unstoppable destabilizing force in the coming decades, particularly for West Antarctica. In other areas, it is losing ice, and more rapidly.

One gigatonne of ice is enough water to fill 400,000 Olympic-sized swimming pools. For the Science study, they fed the readings from ICESat and ICESat-2 into a computer model that converted changes in volume into changes in mass. And with some ice shelves retreating in area in the intervening years, there will be mass losses that have simply been omitted from the calculations.

In Antarctica, detailed measurements showed that the ice sheet is getting thicker in parts of the continent's interior as a result of increased snowfall, according to the study.

However, the research found that gains from accumulated snow is outweighed by the loss of ice on the coast. In those places, the loss is due to warming from the ocean.

"This is a much more significant climatic signal than what you might see if you just surveyed for two or three years", Professor Smith said. ICESat-2 measured that the Kangerdulgssuaq and Jakobshavn glaciers have lost between 4 and 6 meters (14 and 20 feet) of ice per year, for example.

In Antarctica, the prime areas for ice loss are West Antarctica and the Antarctic Peninsula, where warmer seas are melting the ice.

The majority of this ice loss was from thinning of coastal glaciers, which have been impacted by warmer summer temperatures melting the ice on the surface, and warmer ocean temperatures eroding the edges of the ice.

"'It's not like any instrument that we've had in space before, ' said another of the authors, Alex S. Gardner, a glaciologist at NASA's Jet Propulsion Laboratory in Pasadena, Calif".

"The result is a fantastically detailed look at how the ice sheets are changing over a 15+ year period", Ted Scambos, a senior research scientist at the University of Colorado's Earth Science and Observation Centre who was not involved in the study, told Earther. "'Now we've got it all on the same map, which is a really powerful thing, ' said Dr. Fricker, a glaciologist at the Scripps Institution of Oceanography in La Jolla, Calif". Some have rough surfaces, with crevasses and ridges, but the precision and high resolution of ICESat-2 allows researchers to measure overall changes.

The study looked at the changes in the Greenland ice sheet as well.

From the frozen crags of the Andes and the Rockie mountains to the ice sheets covering Greenland and Antarctica, the world's ice has been melting at an accelerated rate in the last five years. Blues show smaller rates of ice gain in the interior of the ice sheet.

While ice shelves, which float on the ocean, don't contribute to sea level rise, they act like a barrier, anchoring glaciers on the Antarctic landmass.

The findings show how the massive ice sheets at the far ends of the planet will affect millions of people on coastlines everywhere. But ice shelves act as buttresses against the grounded ice behind them; when they thin they allow that ice to flow faster.

Other reports by Click Lancashire

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