Antarctic ice melting faster

James Marshall
June 14, 2018

The melt rate has tripled in the past decade, the study concluded. If the acceleration continues, some of scientists' worst fears about rising oceans could be realized, leaving low-lying cities and communities with less time to prepare than they'd hoped.

A group of 80 Antarctic experts said that in the two decades prior to 2012, the continent lost about 76 billion tons of ice annually, which caused about 0.2 millimeters of sea-level rise a year.

Enlarge / Changes in Antarctica's ice since 1992, shown for three regions and in total.

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The complex, multi-pronged nature of this effort means that researchers frequently publish separate estimates of change based on the type of data they are collecting, rather than integrating all sources of information.

This assessment, conducted by 84 scientists from 44 global organizations, is known as the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE).

It uses combined satellite data to measure the Antarctic ice sheet's changing flow and volume. The lead author was Andrew Shepherd of the University of Leeds in the United Kingdom.

"The detailed record shows an acceleration, starting around 2002, " said Beata Csatho, one of the study authors and a glaciologist at the State University of NY at Buffalo, in an email.

Jumping straight to that result, IMBIE finds that Antarctica lost 2,720 ± 1,390 gigatons of ice in that time period-enough to raise global sea level 7.6 millimeters on its own. Forty percent of that loss has occurred in just the last 5 years, again underscoring the increase in losses recently.

Looking closer, the rapid, recent changes are nearly entirely driven by the West Antarctic ice sheet, which scientists have long viewed as an Achilles' heel.

The greatest change in annual ice loss was in West Antarctica, averaging around 58 billion tons in the years leading up to 2012, then skyrocketing to 175 billion tons per year in the five years since.

Sea level contribution due to the Antarctic ice sheet between 1992 and 2017.

Pine Island is now losing about 45 billion tons per year, and Thwaites is losing 50 billion. The West Antarctic Ice Sheet is far more vulnerable to melting because its bowl-shaped bedrock drops below sea level, and most of its glaciers contact the ocean.

However, he said that there is growing evidence that projections of Antarctica's influence on sea-level rise may have been underestimated.

Because the East Antarctic Ice Sheet generally sits on higher bedrock and isn't as susceptible to warming ocean water, a warmer atmosphere can bring increased snowfall that temporarily outweighs losses.

Finally, the largest part of the continent, East Antarctica, has remained more stable and didn't contribute much ice to the ocean during the period of study, the assessment says.

That might not sound like much, but what's particularly concerning is the way the ice loss has sharply accelerated over the course of the 25-year timeframe.

Even more grim, a half-century of high emissions by this point would have locked in more than 10 metres (33 ft) of future sea level rise in coming millennia - and could potentially lead to more than 50 metres of sea level rise over the next 10,000 years.

"According to our analysis, there has been a step increase in ice losses from Antarctica during the past decade, and the continent is causing sea levels to rise faster today than at any time in the past 25 years".

"We can not count on East Antarctica to be the quiet player, and we start to observe change there in some sectors that have potential and they're vulnerable, " said Velicogna.

Per the team's calculations, a high emissions scenario - in which carbon emissions rise unabated and environmental protections in Antarctica are not implemented - global air temperature would rise almost 3.5°C above 1850 levels by 2070, with sea level rise averaging somewhere between 10-15 mm every year.

That's adding 0.6 of a millimetre to sea levels each year. "The general consensus in glaciology was that ice sheets couldn't change rapidly - but that's not the case", Shepherd said. "We will not necessarily see exclusively rapid retreat, " said Christianson, noting that as glaciers like Pine Island retreat backwards down a submarine, downhill slope, they will sometimes encounter bumps that slow down their movement. However, he says that now the data is tracking a higher scenario, which could mean almost 6 inches of additional sea level rise in the next century.

Antarctica is far from uniform, and one number can't tell the whole story. Together, the studies evaluate past and present conditions in Antarctica to determine the impact of climate change and human activity on the continent, and to present strategies for the future of its ecology and geology.

Or alternatively, he continued, Antarctica could drive faster changes, ones that "begin to exceed what we're going to be able to cope with".

Other reports by Click Lancashire

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