NASA
satellites bearing advanced laser technology have recorded the most
accurate picture of large scale ice sheet melting in Greenland and
Antarctica to date.
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
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.
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.
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.
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 ice
on the land and ice floating on the sea, whereas previous studies
focused on just one or the other.
"We know that ice
on land responds to ice on 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 sea
ice has previously been excluded because melting ice on land directly
contributes to sea level rises, whereas sea ice melt 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."
"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.
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."
The latest data showed melting was more extreme in Greenland than in Antarctica.
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