Satellites Show Melting Ice Sheets In Antarctica And Greenland Have Contributed To 14 mm Sea Level Rise In 16 Years

ABC Science - Zoe Kean

Loss of ice from the margins of Antarctica outweighs the gains in the interior of the continent. (Supplied: British Antarctic Survey)

Key Points NASA satellites help scientists track Greenland and Antarctica’s contribution to sea level rise Melting Antarctic ice shelves lead to glaciers flowing into the sea More research is needed to understand how East Antarctica is responding to climate change

NASA satellites bearing advanced laser technology have recorded the most accurate picture of large scale ice sheet melting in Greenland and Antarctica to date.

Melting ice sheets in Greenland and Antarctica contributed to 14 millimetres of sea level rise between 2003 and 2019, according to a study published today in the journal Science.

"[Into the future] with that 14 millimetres happening every 16 years, it adds up to a pretty significant amount of sea level rise", said lead author Benjamin Smith of the University of Washington.

If all the melt observed in this study was to flood an area the size of Australia, we would all be wading through 66 centimetres of water, Professor Smith calculated.

Two satellites, the ICESat-1 and the more advanced ICESat-2, were equipped with "laser altimeters" that bounced light pulses off the ice sheets to determine their height.

Researchers compared measurements taken in the early 2000s by ICESat-1 with measurements taken in 2018 and 2019 by ICESat-2.

"The two sets of measurements intersect each other at millions of points, it's those intersections that let us map how the ice changed between ICESat-1 and ICESat-2," Professor Smith said.

"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.

Greenland vs Antarctica

Previous satellite data from NASA shows the rate of global mean sea level rise is accelerating by an average of 3.4 millimetres per year.

Melting ice from Greenland and Antarctica contributes to about a third of the sea level rise we're seeing, Professor Smith said.

The latest data showed melting was more extreme in Greenland than in Antarctica.

Greenland's ice cap calving (Gfycat)

Greenland's ice sheet lost an average of 200 gigatons of ice a year, contributing up to two thirds of the sea level rise. 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.

"Greenland melts at the surface quite a bit every year whereas the surface of Antarctica does not melt over a significantly large areas of the continent," he said.

The satellite data showed Antarctica lost an average of 118 gigatons of ice in the same time frame.

While there are gains in ice coverage in the interior, due to increased snowfall, these did not outweigh the losses in coastal areas.

"The total amount of thinning vastly outweighs the small amount of thickening in the interior of the ice sheets," Professor Smith said.

Satellite data shows the amount of ice gained (blue) or lost (red and purple) by Antarctica between 2003 and 2019 (Supplied: Smith et al/Science)

The majority of Antarctica's contribution to sea level rise comes from its glaciers flowing into the ocean as warmer water erodes the ice. This process is far more rapid in West Antarctica than in East Antarctica where it is quite patchy, with areas of thickening and thinning.

Measuring ice shelf losses

Glaciologist Matt King said a strength of this research is that it observed both grounded ice such as glaciers and land ice extending onto the sea, whereas previous studies focused on just one or the other.

"We know that ice on land responds to ice extending onto the sea, so looking at the ice sheet as a whole is an advance," said Professor King of the University of Tasmania.

Study co-author Helen Amanda Fricker of the University of California said land-based ice that extends out to sea has previously been excluded because melting ice on land directly contributes to sea level rises, whereas ice that floats on water does not.

But, she said, scientists need to know how ice sheets are changing if we are going to be able to predict how grounded ice might leave the Antarctic continent.

"Knowing this won't slow it down, but it will help us make informed decisions."

The anatomy of an ice shelf. (Supplied: Dr Sue Cook)

"We have discovered that where grounded ice changes most is where the ice shelves are thinning," said Professor Fricker 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.

"Antarctica functions a bit like a giant apple pie, when the crust is removed, the filling leaks out."

Research needed where Australia is based

Professor Fricker is calling for more on-the-ground research in East Antarctica, where Australia's research bases are located.

"Key systems are changing in East Antarctica, it's in Australia's backyard," she said.

Professor King agreed.

"Satellite studies provide a great continental view, but we also need good field measurements to understand what's going on in these vulnerable places," said Professor King.

"We don't really know enough about East Antarctica to understand the changes going on," he said.

"So we are left with a general state of confusion, flying blind from both directions."

Links

• 'Very Un-Antarctic': When The Icy Continent Was Not Very Cold At All
• Guest Post: How Close Is The West Antarctic Ice Sheet To A ‘Tipping Point’?
• Antarctica Logs Hottest Temperature On Record With A Reading Of 18.3C
• Past Antarctic Ice Melt Reveals Potential For 'Extreme Sea-Level Rise'
• If Warming Exceeds 2°C, Antarctica’s Melting Ice Sheets Could Raise Seas 20 Metres In Coming Centuries
• Iceberg The Size Of Sydney Breaks Off Amery Ice Shelf In Antarctica
• Devastating Simulations Say Sea Ice Will Be Completely Gone In Arctic Summers By 2050
• Arctic Climate Change – It’s Recent Carbon Emissions We Should Fear, Not Ancient Methane ‘Time Bombs’
• The Arctic May Have Crossed Key Threshold, Emitting Billions Of Tons Of Carbon Into The Air, In A Long-Dreaded Climate Feedback
• Climate Change: Arctic Permafrost Now Melting At Levels Not Expected Until 2090
• Melting Permafrost In Arctic Will Have $70tn Climate Impact – Study
• Melting Arctic Ice Is Now Pouring 14,000 Tons Of Water Per Second Into The Ocean, Scientists Find