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Panorama comments on Open thread, Nov. 02 - Nov. 08, 2015 - Less Wrong Discussion

4 Post author: MrMind 02 November 2015 10:07AM

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Comment author: Panorama 05 November 2015 08:32:15PM 2 points [-]

NASA Study: Mass Gains of Antarctic Ice Sheet Greater than Losses

A new NASA study says that an increase in Antarctic snow accumulation that began 10,000 years ago is currently adding enough ice to the continent to outweigh the increased losses from its thinning glaciers.

The research challenges the conclusions of other studies, including the Intergovernmental Panel on Climate Change’s (IPCC) 2013 report, which says that Antarctica is overall losing land ice.

According to the new analysis of satellite data, the Antarctic ice sheet showed a net gain of 112 billion tons of ice a year from 1992 to 2001. That net gain slowed to 82 billion tons of ice per year between 2003 and 2008.

“We’re essentially in agreement with other studies that show an increase in ice discharge in the Antarctic Peninsula and the Thwaites and Pine Island region of West Antarctica,” said Jay Zwally, a glaciologist with NASA Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study, which was published on Oct. 30 in the Journal of Glaciology. “Our main disagreement is for East Antarctica and the interior of West Antarctica – there, we see an ice gain that exceeds the losses in the other areas.” Zwally added that his team “measured small height changes over large areas, as well as the large changes observed over smaller areas.”

Comment author: Manfred 05 November 2015 10:36:42PM 2 points [-]

Interesting. Obviously if some place is still below freezing all year round (i.e. the bulk of East Antactica), global warming can easily increase ice mass due to increased snowfall. But I'd thought decrease in total ice mass was pretty well-established.

Comment author: CellBioGuy 06 November 2015 12:11:22AM *  8 points [-]

The amount lost in the Arctic is about a factor of 3 larger than the net gain in Antarctica, and West Antarctica as a subset of antarctica is losing ice on the net in a way that is likely to accelerate in the future. Also apparently Antarctica has been gaining ice on the net for 10,000 years according to the source, and it's a case of recent loss rate increases not yet balancing this normal gain rate.

Further quote from the article:

“If the losses of the Antarctic Peninsula and parts of West Antarctica continue to increase at the same rate they’ve been increasing for the last two decades, the losses will catch up with the long-term gain in East Antarctica in 20 or 30 years -- I don’t think there will be enough snowfall increase to offset these losses.”

Comment author: Manfred 15 January 2016 07:23:23AM *  2 points [-]

A late follow-up. I read an article on the study, and it turns out that the difference from previous estimates (which basically all showed a decrease in antarctic ice mass) comes from an interesting place. Everyone agrees on the height change in East Antarctica. But the studies that got a net decrease assumed that the change in height was due to recently increased snowfall, in which case the extra height will have the density of snow. This new study that gets a net mass increase assumes that the change in height is actually part of a long-term mass rebound from the last minimum, and if that's true then the density profile of the Antarctic ice sheet should be roughly constant, and the extra height will have the density of ice, which is ~3x that of snow.

I think the disagreement over this shows how big our error bars are.

Comment author: knb 06 November 2015 05:02:40AM 1 point [-]

This seems significant, but I'm not sure how to interpret it... Is it good news the ice sheet isn't shrinking or bad news that the sea level rise apparently came from other sources without us noticing?

Comment author: Lumifer 06 November 2015 03:33:58PM 1 point [-]

the sea level rise apparently came from other sources

Which sea level rise?

Comment author: CellBioGuy 07 November 2015 09:57:56PM *  3 points [-]

http://www.worldviewofglobalwarming.org/images11/SeaLevelRiseRateChart2010.jpg

This is the global mean. Rise measured at any given actual shoreline will be different and sometimes even falling, due to local geology altering elevations of land at not-dissimilar rates in some areas (especially areas where post-glacial rebound is still occurring) as well as thermal expansion being uneven.

Comment author: Good_Burning_Plastic 08 November 2015 10:40:02AM 1 point [-]

Was something weird happening in the 1920s or is it just an optical illusion due to the black lines?

Comment author: CellBioGuy 12 November 2015 02:26:38AM 0 points [-]

I think you'd see similar anomalies in 1880 and 1985 stand out with similar lines.

Comment author: Lumifer 08 November 2015 05:32:34AM 0 points [-]

Yes. But the sea levels have been rising continuously since the time of the last glacial maximum. 10,000 years ago they were rising at a rather more dramatic rate, too.

Comment author: CellBioGuy 08 November 2015 09:29:34AM *  1 point [-]

Yep! My favorite bit of what went on during the end of the last glaciation is the way that it happened unevenly, a sedate constant flow of water from ice to the oceans interrupted by centuries here and there where sea level rose by at least 2-5 centimeters a year. Presumably that's what happens once an ice sheet becomes unstable and pieces of them collapse quickly and nonlinearly.

Comment author: Lumifer 09 November 2015 04:19:35PM 1 point [-]

That was one of those "interesting times to live in"? Still it's peanuts compared to the mother of all floods :-)

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