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West Antarctica's ice sheet loss "appears unstoppable"

by Greg Bernhardt
Tags: antarctica, appears unstoppable, loss, sheet, west
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Greg Bernhardt
#1
May13-14, 12:34 PM
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Sea level appears destined to rise at least 4ft. Anyone have data on how this will affect the world's coastlines?

A new study by researchers at NASA and the University of California, Irvine, finds a rapidly melting section of the West Antarctic Ice Sheet appears to be in an irreversible state of decline, with nothing to stop the glaciers in this area from melting into the sea.
These glaciers already contribute significantly to sea level rise, releasing almost as much ice into the ocean annually as the entire Greenland Ice Sheet. They contain enough ice to raise global sea level by 4 feet (1.2 meters) and are melting faster than most scientists had expected. Rignot said these findings will require an upward revision to current predictions of sea level rise.
West Antarctic Glacier Loss Appears Unstoppable
http://www.jpl.nasa.gov/news/news.php?release=2014-148

The 'Unstable' West Antarctic Ice Sheet: A Primer
http://www.jpl.nasa.gov/news/news.php?release=2014-147
Phys.Org News Partner Earth sciences news on Phys.org
mheslep
#2
May13-14, 02:17 PM
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Rate? Apparently melting the *entire* Western sheet is a 4000 year process. The lead author of the paper leading to the recent news, Rignot, said previously:

In terms of time scales, I do not think the results of this study are relevant to what will be happening in the next 100 years and beyond. The problem is far more complex. But this is a step forward.


Dotearth
RocketSci5KN
#3
May13-14, 05:23 PM
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Al Gore should go down there and stop it from moving...

Bobbywhy
#4
May13-14, 11:15 PM
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West Antarctica's ice sheet loss "appears unstoppable"

Quote Quote by Greg Bernhardt View Post
Sea level appears destined to rise at least 4ft. Anyone have data on how this will affect the world's coastlines?
Here is a map that shows how North American coastlines will be affected by sea level rise:

http://sealevel.climatecentral.org/surgingseas/

Bobbywhy
phyzguy
#5
May15-14, 09:19 AM
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Sea level appears destined to rise at least 4ft. Anyone have data on how this will affect the world's coastlines?
This NOAA web site gives histograms of how much of the Earth's land area is at different elevations. According to Figure 2, the slope of the curve near the current sea level is 3.69E5 km^2/m. Since the current land area of the Earth is 1.49E8 km^2, this means that the impact is a loss of 0.25% of the Earth's land area per meter of sea level rise. While this is not a good thing if you live near the sea, it is hardly a catastrophe, especially since it will take hundreds to thousands of years to occur, giving people a chance to adapt. If you consider a city like New York(where I live), virtually none of the current infrastructure (buildings, subways, streets, ...) will last more than a few hundred years. So it will all need to be rebuilt in the next few hundred years anyway. Likely our descendants will decide to build their cities a little further from the sea.
mheslep
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May15-14, 09:49 AM
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Quote Quote by phyzguy View Post
....If you consider a city like New York(where I live), virtually none of the current infrastructure (buildings, subways, streets, ...) will last more than a few hundred years. So it will all need to be rebuilt in the next few hundred years anyway. Likely our descendants will decide to build their cities a little further from the sea.
Why? The Dutch have not gone anywhere.
phyzguy
#7
May15-14, 10:21 AM
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Quote Quote by mheslep View Post
Why? The Dutch have not gone anywhere.
Good point. New York is actually fairly easy to protect from rising sea levels. Dikes at the current locations of the Verazzano Narrows and Hutchison bridges, as shown in the attached map, would protect much of the city from rising sea levels for at least the next thousand years. These have actually been discussed in response to the Hurricane Sandy flooding. I suspect they will be built at some point in the future, but no one will want to spend the money until they are really needed.
Attached Files
File Type: pdf New_York_Dikes.pdf (93.4 KB, 5 views)
klimatos
#8
May20-14, 06:50 PM
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Over the last 2.5 million years, the Earth has experienced more than a hundred Ice Ages and an equivalent number of interglacial periods. These are the result of orbital-forcing, not carbon-dioxide forcing (see Milankovitch Cycles). There have been ten full cycles in the last million years.

During the many interglacials, both the Antarctic and the Greenland ice sheets have experienced significant melting, but in no case have they ever disappeared. They grow back again during the succeeding Ice Ages. We are currently some 20,000 years into an expected 50,000 year warming cycle. If the coming interglacial is anything like the last one, we can expect the world ocean to rise some 13 to 20 feet higher than it is at present.

Al Gore used some of the proceeds from his movie, An Inconvenient Truth, to buy a condo on Fisherman's Wharf in San Francisco. The building sits about four feet above current sea level. If Al isn't worried, I'm not.
jim hardy
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May20-14, 10:20 PM
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We'll do what humans do best - adapt.

First, though, Congress should repeal the "National Flood Insurance Program" .
mheslep
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May21-14, 09:04 AM
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Quote Quote by jim hardy View Post

First, though, Congress should repeal the "National Flood Insurance Program" .
Now there is a common sense proposal, sure to be opposed fanatically by owners of multimillion dollar beach front properties.
jim hardy
#11
May21-14, 10:42 AM
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I grew up in South Florida. There is a fascinating little book , "Land from the Sea" by a U of Miami geology professor.

http://www.amazon.com/Land-Sea-Geolo.../dp/0870242687

Author says about 20,000 years ago sea level dropped about twenty feet and South Florida, then a shallow sandbar like much of today's Bahamas Bank , appeared.

So - it's not like sea level change should be a surprise..

This fellow says measured level at Key West Harbor rose 0.73 feet(~9 inches) from 1913 to 2006. One would have to be really observant to notice that in his lifetime.

http://www.keyshistory.org/Global_Warming.html
Cormagh
#12
May21-14, 10:47 AM
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It seems that the Southern Hemisphere sea ice anomaly has risen since about 1987. This tends to explain the slowdown we are experiencing in sea level rise. http://arctic.atmos.uiuc.edu/cryosph....antarctic.png
Borek
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May21-14, 01:29 PM
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Quote Quote by jim hardy View Post
Author says about 20,000 years ago sea level dropped about twenty feet
20 feet? Up (or rather down) to 400 feet.

http://en.wikipedia.org/wiki/Doggerland
jim hardy
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May21-14, 01:49 PM
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I'm looking for that old book by Hoffmeister. I quoted from memory...... i read it 40 years ago

He's cited in a lot of works, but i've not yet found the right paragraph...

if i'm off by 100 millenia, well so be it ; and i will do apologize.


will continue looking.

old jim

http://www2.fiu.edu/~whitmand/Courses/Fl_geo_notes.html
Geology


The surficial deposits that form these features are very young. All are less than 6 MY old. Most formed around 120,000 years ago (Pleistocene) during an interglacial period when sea level was ~ 25 ft higher -- pamlico shoreline

Most surficial features are related to depositional environments formed during this latter sea level high stand. These environments are reflected by several different geological units (formations) -- see fig 2 in handout -- generally the of the same age. These formations gradually grade from one type to another. The relative age at a given site is determined by local stratagraphic relationships.

Miami fm.

contains oolitic and bryozoan facies
thickest beneath coastal ridge ~40' thins to west
Oolite limestone forms coastal ridge in eastrn Dade Co. Often misidentified as coral rock.
Oolitic facies formed from a shallow offshore bar composed of ooid sand which was reworked by waves and currents
characteristic cross bedding
often disturbed by bioturbation
several good exposures: Silver bluff S. Bayshore Drive, Coco Plum Circle
Bryozoan facies is found in western Dade Co. (see map). Formed in a shallow tidal lagoon to the west of the sand bar.
Bryozoans "moss animals" secrete calcareous skeletons; live in shallow lagoon environments
Depositional environment in South Florida 120,000 years ago was similar to environment in parts of the Bahamas today.
mheslep
#15
May21-14, 02:12 PM
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Last 140ka From paleo data and corals. No error bars, but surely imagine them expanding greatly going back in time.



http://www.cmar.csiro.au/sealevel/sl_hist_intro.html

Better res. last 22ka
http://www4.ncsu.edu/~jpliu/sealevel...l_Sealevel.jpg
D H
#16
May21-14, 02:16 PM
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Quote Quote by Cormagh View Post
It seems that the Southern Hemisphere sea ice anomaly has risen since about 1987. This tends to explain the slowdown we are experiencing in sea level rise. http://arctic.atmos.uiuc.edu/cryosph....antarctic.png
What slowdown in sea level rise?



Source: http://sealevel.colorado.edu/content...gnals-retained


You posted a link to a graph of the Antarctic sea ice anomaly, which is quite different from the topic of this thread. This thread is about the West Antarctica ice sheet. It's the melting of ice sheets and glaciers and the warming of the ocean that causes sea level rise. Sea ice? Not really. It's floating.

The melting of the West Antarctica and Antarctic Peninsula ice sheets contributes to the seemingly paradoxical increase in Antarctic sea ice extent. That newly arriving fresh water floats atop the more dense sea water. Fresh water freezes more easily than does sea water. The summertime loss of ice from those ice sheets becomes a wintertime increase in sea ice.

Other causes include a strengthening of the winds that encircle Antarctica and increased precipitation in the Antarctic. The strengthened winds open up polynyas in the sea ice, stretches of open water surrounded by ice. Those open stretches of water are much easier to freeze than is water shielded by a blanket of ice. The increased precipitation has the same effect as ice sheet melting. It adds easy-to-freeze fresh water to the surface.

References:

Abram, N. et al., "Evolution of the Southern Annular Mode during the past millennium," Nature Clim. Change, (2014)

Shepherd, A. et al., "A Reconciled Estimate of Ice-Sheet Mass Balance," Science 338.6111 (2012): 1183-1189.

Rignot, E. et al., "Ice-Shelf Melting Around Antarctica," Science 341.6143 (2013): 266-270.

Zhang, J., "Increasing Antarctic sea ice under warming atmospheric and oceanic conditions," J. Climate 20 (2007), 2515-2529.

Zhang, J., "Modeling the Impact of Wind Intensification on Antarctic Sea Ice Volume," [i]J. Climate[/i[ 27 (2014), 202214.
mheslep
#17
May21-14, 02:49 PM
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Long term ~3mm/yr, but 2005-2012 was 1.1 0.8 mm/yr

NOAA, The Budget of Recent Global Sea Level Rise 20052012

The sum of steric sea level rise and the ocean mass component has a trend of 1.1 0.8 mm/a over the period
Jason I-II based altimetry comes in a bit higher at 1.6 mm/yr 0.8

also:

Ablain et al, "A new assessment of global mean sea level from altimeters highlights a reduction of global trend from 2005 to 2008", Ocean Sci. Discuss., 6, 31-56, 2009

Abstract. A new error budget assessment of the global Mean Sea Level (MSL) determined by TOPEX/Poseidon and Jason-1 altimeter satellites between January 1993 and June 2008 is presented. We discuss all potential errors affecting the calculation of the global MSL rate. We also compare altimetry-based sea level with tide gauge measurements over the altimetric period. This allows us to provide a realistic error budget of the MSL rise measured by satellite altimetry. These new calculations highlight a reduction in the rate of sea level rise since 2005, by ~2 mm/yr. This represents a 60% reduction compared to the 3.3 mm/yr sea level rise (glacial isostatic adjustment correction applied) measured between 1993 and 2005. Since November 2005, MSL is accurately measured by a single satellite, Jason-1. However the error analysis performed here indicates that the recent reduction in MSL rate is real.
jim hardy
#18
May21-14, 03:02 PM
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Thanks mhslep, looks like i'm off by that 100k years.
Apologies are hereby tendered.

old jim


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