From the University of Southampton
A new study of satellite data from the last 19 years reveals that fresh water from melting glaciers has caused the sea-level around the coast of Antarctica to rise by 2cm more than the global average of 6cm.
Researchers at the University of Southampton detected the rapid rise in sea-level by studying satellite scans of a region that spans more than a million square kilometres.
The melting of the Antarctic ice sheet and the thinning of floating ice shelves has contributed an excess of around 350 gigatonnes of freshwater to the surrounding ocean. This has led to a reduction in the salinity of the surrounding oceans that has been corroborated by ship-based studies of the water.
“Freshwater is less dense than salt water and so in regions where an excess of freshwater has accumulated we expect a localised rise in sea level,” says Craig Rye, lead author of the paper that has been published in the journal Nature Geoscience.
In addition to satellite observations, the researchers also conducted computer simulations of the effect of melting glaciers on the Antarctic Ocean. The results of the simulation closely mirrored the real-world picture presented by the satellite data.
“The computer model supports our theory that the sea-level rise we see in our satellite data is almost entirely caused by freshening (a reduction in the salinity of the water) from the melting of the ice sheet and its fringing ice shelves,” says Craig.
“The interaction between air, sea and ice in these seas is central to the stability of the Antarctic Ice Sheet and global sea levels, as well as other environmental processes, such as the generation of Antarctic bottom water, which cools and ventilates much of the global ocean abyss.”
The research was carried out in close collaboration with researchers at the National Oceanography Centre and the British Antarctic Survey.
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The full paper Rapid sea-level rise along the Antarctic margins in response to increased glacial discharge is published in Nature Geoscience.
Rapid sea-level rise along the Antarctic margins in response to increased glacial discharge
Craig D. Rye, Alberto C. Naveira Garabato, Paul R. Holland, Michael P. Meredith, A. J. George Nurser, Chris W. Hughes, Andrew C. Coward & David J. Webb
- Nature Geoscience (2014) doi:10.1038/ngeo2230
The Antarctic shelf seas are a climatically and ecologically important region, and are at present receiving increasing amounts of freshwater from the melting of the Antarctic Ice Sheet and its fringing ice shelves1, 2, primarily around the Antarctic Peninsula and the Amudsen Sea. In response, the surface ocean salinity in this region has declined in past decades3, 4, 5, 6, 7, 8, 9. Here, we assess the effects of the freshwater input on regional sea level using satellite measurements of sea surface height (for months with no sea-ice cover) and a global ocean circulation model. We find that from 1992 to 2011, sea-level rise along the Antarctic coast is at least 2 ± 0.8 mm yr−1 greater than the regional mean for the Southern Ocean south of 50° S. On the basis of the model simulations, we conclude that this sea-level rise is almost entirely related to steric adjustment, rather than changes in local ocean mass, with a halosteric rise in the upper ocean and thermosteric contributions at depth. We estimate that an excess freshwater input of 430 ± 230 Gt yr−1 is required to explain the observed sea-level rise. We conclude that accelerating discharge from the Antarctic Ice Sheet has had a pronounced and widespread impact on the adjacent subpolar seas over the past two decades.
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Fortunately, they provide an SI file, seen here: http://www.nature.com/ngeo/journal/vaop/ncurrent/extref/ngeo2230-s1.pdf
Figure S4 is telling:
It seems there is a “pause” that has developed in SLR around Antarctica starting around 2005 continuing through 2012.
For reference, this map from NOAA/NESDIS shows that there is in fact about 2 cm of SLR around some parts of Antractica, but the main SLR is a big red patch in the Western Pacific:
While the Rye et al. paper says ice melt from the continent is the cause, it may also be simply a matter of winds. Note that the red spotch of SLR on the map above is mainly an issue of winds and ENSO. Around Antarctica, we have a strong circumpolar wind pattern, as is seen in the video below about ozone over Antarctica:
That circumpolar wind pattern around Antarctica can act as a sea level rise enhancer, as described in this paper:
Rapid subsurface warming and circulation changes of Antarctic coastal waters by poleward shifting winds
Spence et al. 2014
Abstract
The southern hemisphere westerly winds have been strengthening and shifting poleward since the 1950s. This wind trend is projected to persist under continued anthropogenic forcing, but the impact of the changing winds on Antarctic coastal heat distribution remains poorly understood. Here we show that a poleward wind shift at the latitudes of the Antarctic Peninsula can produce an intense warming of subsurface coastal waters that exceeds 2 °C at 200-700 m depth. The model simulated warming results from a rapid advective heat flux induced by weakened near-shore Ekman pumping, and is associated with weakened coastal currents. This analysis shows that anthropogenically induced wind changes can dramatically increase the temperature of ocean water at ice sheet grounding lines and at the base of floating ice shelves around Antarctica, with potentially significant ramifications for global sea level rise.
Bottom line: I’m not much worried about the claims made about SLR in Antarctica being due to ice melt. There may be some enhancement, but to say it is the sole reason, when other fcators are clearly at play is just your typical climate alarmism at work.
UPDATE: Having written this piece late in the evening, my fatigue must have caused me to forget this graphic. Temperature over Antarctica seems to to be ever so slightly negative trending.
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The ice ballyhoo seems pretty simple to me.
According to the national sea and ice center, sea ice extent was 1.03 million square kilometers (398,000 square miles) below the 1981 to 2010 long-term average and 1.42 million square kilometers (548,000 square miles) above that observed in 2012 on the same date.
At the Antarctic, sea ice remains at a daily record high, and 1.19 million square kilometers (459,000 square miles) above the 1981 to 2010 average.
So at the poles in total, the extent of ice is currently 61,000 sq miles above the 1981-2010 trend.
The world is hotter than ever!!!™ and yet there is more ice at the poles than in 30 years.
GO SANTA!!!
p.s. which is not to denigrate in any way the fine work of all the elves
Sea level in Antarctic coast increased 2 cm more than Southern Ocean mean. 430 Gt/yr ice mass loss needed to explain sea level rise. GRACE data estimates only 29 to 126 Gt/yr.
http://www.nature.com/nature/journal/v491/n7425/full/nature11621.html
The UAH temperature graph shows cooling trend in Antarctica since 1978. How to reconcile all these inconsistencies? Ice water is at 0 Celsius. Specific volume of water at 0 C is greater than at 4 C. If ice water mixes and cools seawater down to 100 meters deep. The volume increase is 2 cm high. The final temperature is > 0 C but ice water adds to the volume.
It is strange that with all this alleged extra global warming in the Antarctic, yet the Southern oceans SST anomaly has been declining since 1981 from about +0.3 C to about -0.2 C as Bob Tisdale’s graphs show every month
kevin lenihan (@kevinlenihan1) says: September 1, 2014 at 5:45 pm Can I ask some newbish amateur questions? Maybe someone will tackle a few of these for me. If so, much obliged.
(1) if there is increasing sea ice at the Antarctica, won’t that have the effect of raising local sea levels, like dropping ice cubes in a glass? I mean if the ice increases are due to freezing seas, maybe not. But if they are due to increased atmospheric moisture coming into the region, such as from snow, wouldn’t that raise local seas?
ADH – Depends where the sea ice came from. If from freezing the sea water, should be no change, the ice floes will occupy the same amount of space below sea level as they would if melted. Straightforward Archimedes. If the ice has slid off the land, the sea level will rise, but this will be a temporary rise as the excess water will flow north to equalize sea levels.
(2) I realize global warming predicts melting ice sheets at the poles. But it seems to me that a warming world would increase ice at the poles, unless the temperatures rose enough where it was above freezing. It seems to me that a warming world will have more moisture in the air. Moisture which will fall as snow in Antarctica, thereby growing the ice sheets.
ADH The temperature inland in Antarctica is so low that absolute humidity is exceedingly low. Hardly any extra snow will be deposited (hence the great age available in ice cores – not enough new snow to melt the bottom layer). But at the edge, where sea water and ice exist, the temperature will for part of the year be above freezing, and there will be greater humidity, and it is plausible that snow/sleet/rain will fall and be frozen on contact with very cold ice, and there may be more ice created than is destroyed.
(3) if there has been a 17 year pause in warming, why would the Antarctic ice sheets be melting?
ADH It all depends on what happens at the edge, where the sea is in contact with the ice. Sea water is above freezing point so there will be a tendence for ice to melt. There will also be a tendency for water to freeze. Reduce the speed of the ocean currents, more likely that the ice will freeze the near stationary water. Increase the speed of the currents, the cold water will be replaced by more cold water, and it will be more likely that the ice will melt.
(4) I once read about the complications involved with analyzing sea levels. Continents are moving, sinking, rising. And land is sinking or rising depending on local conditions. The land is rising in many places as it has been since the end of the last ice age when ice pressed the land in. Measuring sea levels seems so complicated and involves so many elaborate considerations and algorithms that only the people making that it requires one to place an inordinate level of trust in the people designing those measurements. Is there any reason I should trust the objectivity of these handful of scientists doing the studies? Are there honest peers checking and duplicating their methods? It seems to me measuring minute levels of sea level rise over a small period of time must have a margin of error that is larger than the claimed increase. And I fear that the value of the bias which is built into these studies is larger than the small increments of sea rise being claimed.
ADH Very complicated in NW Europe, Canada and the USA, which were all subjected to glaciations, and the ‘solid’ crust is bouncing up and down – albeit very slowly. Antarctica has been glaciated for millions of years, there should be negligible uplift or sinking of the crust there, apart from in the volcanic areas. So simple tide gauges should suffice. However, SFAIK, the data from satellites re sea levels is available to all ‘scientists’ who are interested in sea levels, and not all are weeded to the CAGW religion. So when someone writes a paper, others read it and if it looks wrong, they may check, if they have time. So while not necessarily ‘peer reviewed’ in the usual sense, it is unlikely that really bad errors will be made, and not picked up. As to what margins of error there may be, this should be stated in the paper. If not, beware!!!!!