Antarctica losing six times more ice mass annually now than 40 years ago

Antarctica losing six times more ice mass annually now than 40 years ago – “We expect multi-meter sea level rise from Antarctica in the coming centuries”

Desdemona Despair,

14 January, 2018

IRVINE, California, 14 January 2019 (UCI) – Antarctica experienced a sixfold increase in yearly ice mass loss between 1979 and 2017, according to a study published today in Proceedings of the National Academy of Sciences. Glaciologists from the University of California, Irvine, NASA’s Jet Propulsion Laboratory and the Netherlands’ Utrecht University additionally found that the accelerated melting caused global sea levels to rise more than half an inch during that time.

“That’s just the tip of the iceberg, so to speak,” said lead author Eric Rignot, Donald Bren Professor and chair of Earth system science at UCI. “As the Antarctic ice sheet continues to melt away, we expect multi-meter sea level rise from Antarctica in the coming centuries.”

For this study, Rignot and his collaborators conducted what he called the longest-ever assessment of remaining Antarctic ice mass. Spanning four decades, the project was also geographically comprehensive; the research team examined 18 regions encompassing 176 basins, as well as surrounding islands.

Techniques used to estimate ice sheet balance included a comparison of snowfall accumulation in interior basins with ice discharge by glaciers at their grounding lines, where ice begins to float in the ocean and detach from the bed. Data was derived from fairly high-resolution aerial photographs taken from a distance of about 350 meters via NASA’s Operation IceBridge; satellite radar interferometry from multiple space agencies; and the ongoing Landsat satellite imagery series, begun in the early 1970s.

The team was able to discern that between 1979 and 1990, Antarctica shed an average of 40 gigatons of ice mass annually. (A gigaton is 1 billion tons.) From 2009 to 2017, about 252 gigatons per year were lost.

The pace of melting rose dramatically over the four-decade period. From 1979 to 2001, it was an average of 48 gigatons annually per decade. The rate jumped 280 percent to 134 gigatons for 2001 to 2017.

Rignot said that one of the key findings of the project is the contribution East Antarctica has made to the total ice mass loss picture in recent decades.

“The Wilkes Land sector of East Antarctica has, overall, always been an important participant in the mass loss, even as far back as the 1980s, as our research has shown,” he said. “This region is probably more sensitive to climate [change] than has traditionally been assumed, and that’s important to know, because it holds even more ice than West Antarctica and the Antarctic Peninsula together.”

He added that the sectors losing the most ice mass are adjacent to warm ocean water.

“As climate warming and ozone depletion send more ocean heat toward those sectors, they will continue to contribute to sea level rise from Antarctica in decades to come,” said Rignot, who’s also a senior project scientist at JPL.

Co-authors of this study are Jeremie Mouginot, UCI associate researcher in Earth system science; Bernd Scheuchl, UCI associate project scientist in Earth system science; Mathieu Morlighem, UCI associate professor of Earth system science; and Michiel van den Broeke and Jan M. “Melchior” van Wessem of the Netherlands’ Utrecht University. Funding and support were provided by NASA’s cryospheric sciences and Measures programs, the Netherlands Organization for Scientific Research’s polar program and the Netherlands Earth System Science Centre.

Contact

Brian Bell, 949-824-8249, bpbell@uci.edu

https://news.uci.edu/2019/01/14/uci-jpl-study-antarctica-losing-six-times-more-ice-mass-annually-now-than-40-years-ago/

ABSTRACT: We use updated drainage inventory, ice thickness, and ice velocity data to calculate the grounding line ice discharge of 176 basins draining the Antarctic Ice Sheet from 1979 to 2017. We compare the results with a surface mass balance model to deduce the ice sheet mass balance. The total mass loss increased from 40 ± 9 Gt/y in 1979–1990 to 50 ± 14 Gt/y in 1989–2000, 166 ± 18 Gt/y in 1999–2009, and 252 ± 26 Gt/y in 2009–2017. In 2009–2017, the mass loss was dominated by the Amundsen/Bellingshausen Sea sectors, in West Antarctica (159 ± 8 Gt/y), Wilkes Land, in East Antarctica (51 ± 13 Gt/y), and West and Northeast Peninsula (42 ± 5 Gt/y). The contribution to sea-level rise from Antarctica averaged 3.6 ± 0.5 mm per decade with a cumulative 14.0 ± 2.0 mm since 1979, including 6.9 ± 0.6 mm from West Antarctica, 4.4 ± 0.9 mm from East Antarctica, and 2.5 ± 0.4 mm from the Peninsula (i.e., East Antarctica is a major participant in the mass loss). During the entire period, the mass loss concentrated in areas closest to warm, salty, subsurface, circumpolar deep water (CDW), that is, consistent with enhanced polar westerlies pushing CDW toward Antarctica to melt its floating ice shelves, destabilize the glaciers, and raise sea level.

SIGNIFICANCE: We evaluate the state of the mass balance of the Antarctic Ice Sheet over the last four decades using a comprehensive, precise satellite record and output products from a regional atmospheric climate model to document its impact on sea-level rise. The mass loss is dominated by enhanced glacier flow in areas closest to warm, salty, subsurface circumpolar deep water, including East Antarctica, which has been a major contributor over the entire period. The same sectors are likely to dominate sea-level rise from Antarctica in decades to come as enhanced polar westerlies push more circumpolar deep water toward the glaciers.

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This is just plain weird

"What's saved us in the past is carbon dioxide levels have been low enough that sea ice has grown," Levy said.

"We've got to keep emissions as low as we can, otherwise we will go back to levels not seen in 14 million years."

At that time, carbon levels were around 400 parts per million (ppm) - low enough for sea ice to emerge.(sic)

They should refer to this:

The Last Time CO2 Was This High, Humans Didn’t Exist

Rising carbon emissions putting Antarctic ice sheet under threat

Stuff.co.nz,

15 January, 2019

Increasing carbon emissions could propel us into a world that hasn't existed for millions of years, and put the existence of the Antarctic ice sheet under threat.

Those are the findings of a new study published in the Nature Geoscience journal, looking at how sensitive the ice sheet might be to climate change.

Lead author Richard Levy, from GNS Science and Victoria University of Wellington, said the study showed the ice sheet was "highly sensitive" to changes in temperature.

While it would be centuries before any serious changes to the ice sheet took effect, emissions needed to be lowered today to limit the impact. 

SIMON REEVE

Rising sea levels are putting the Antarctic ice sheet under threat.

It was most at risk when the earth's tilt was steeper - as it is now - and polar ranges were more exposed to the sun.

READ MORE:
* Greenland ice melt speeds up
* Polar ice sheets may 'collapse'
* 'Grim future' on the horizon

But unlike other historical periods when the earth was at a steep tilt, this time rising carbon dioxide levels are posing an even greater threat.

But human activity had resulted in levels now going beyond that, putting sea ice at risk if emissions were not kept in check.

"This study adds to our knowledge of the history and behaviour of Antarctica's ice sheets and is yet more proof that urgent action is needed on emissions," said co-author Professor Tim Naish, of Victoria University's Antarctic Research Centre.

"Persistent sea ice appears to have helped maintain a degree of stability in the Antarctic Ice Sheet. We cannot afford to lose it."

The earth took about 40,000 years to complete a cycle from a high tilt to a less dangerous lower one, Levy said.

GAVIN DUNBAR

The Nansen ice shelf. Scientists say the ice sheet in the Antarctic is "highly sensitive" to changes in climate.

"What's saved us in the past is carbon dioxide levels have been low enough that sea ice has grown," Levy said.

"We've got to keep emissions as low as we can, otherwise we will go back to levels not seen in 14 million years."

At that time, carbon levels were around 400 parts per million (ppm) - low enough for sea ice to emerge.