The ice around the edge of Antarctica is melting faster than previously thought, potentially unlocking metres of sea-level rise in the long-term, researchers have warned.
A team of US scientists looked at 18 years’ worth of satellite data and found the floating ice shelves that skirt the continent are losing 310km^3 of ice every year. One shelf lost 18% of its thickness during the period.
The loss of ice shelves does not contribute much directly to sea level rise. But they act like a cork in a bottle at the point where glaciers meet the sea – jamming the flow of ice from the massive ice sheets of east and west Antarctica
(Source: http://www.theguardian.com/environment/2015/mar/26/collapse-antarcticas-glaciers-ice-melt-sooner-than-thought-scientists-warn)
Dear George,
your question is a bit unclear to me. How can a sea level rise around Antarctica affect sea level in the MedSea? I suggest you mean the effect of mass input from Antarctica on the MedSea.
If yes, the following figure provides you the answer. A melting of ice will lead to gravitational changes and a respective redistribution of water into the far field of the ice sheet:
http://www.nature.com/nature/journal/v517/n7535/images/nature14093-sf1.jpg
The figure shows you the dimensionless scaling factors of such "events". You can simply multiply the added mass with the respective scaling factors to get the sea level signal at each grid point. Since the MedSea is in the "far field" it has a positve scaling factor around 1 meaning that 1 mm sea level change coming from Antarctica will lead to roughly 1 mm sea level change in the MedSea.
Hope this answers your question
Dear George,
your question is a bit unclear to me. How can a sea level rise around Antarctica affect sea level in the MedSea? I suggest you mean the effect of mass input from Antarctica on the MedSea.
If yes, the following figure provides you the answer. A melting of ice will lead to gravitational changes and a respective redistribution of water into the far field of the ice sheet:
http://www.nature.com/nature/journal/v517/n7535/images/nature14093-sf1.jpg
The figure shows you the dimensionless scaling factors of such "events". You can simply multiply the added mass with the respective scaling factors to get the sea level signal at each grid point. Since the MedSea is in the "far field" it has a positve scaling factor around 1 meaning that 1 mm sea level change coming from Antarctica will lead to roughly 1 mm sea level change in the MedSea.
Hope this answers your question
The Guardian article you mention is once more a typical example attempting to use the global warming scare to increase the chance of additional funding for further research. First of all you have to ask yourself whether the slight warming of average global temperature tooted by the IPCC can actually be assigned to man-made causes or is it just part of natural climate cyclicity. Remember that man-made climate change is the current catchword used in grant applications, but actual proof is limited or even non-existent.
The statement by prof David Vaughan is a good example: “The rate of ice loss, especially when considered in terms of the percentage of ice lost in the last two decades, is dramatic. This research is a significant step towards improving our ability to predict the future of the Antarctic ice sheet and its contribution to global sea level rise.”
You have to ask yourself whether the ice loss is really dramatic? Check with the best climate data available kept a jour by the Norwegian geology professor Ole Humlum from Oslo, Norway: http://www.climate4you.com/ and click (left blue list) to see the variability of Arctic and Antarctic sea ice extent. You could also check current sea ice extent at: http://nsidc.org/data/seaice_index/index.html and click
To give the statement an air of credibility the text includes: “It is unclear (italics by BW) whether the loss of ice is directly related to man-made climate change or a cyclical change in ocean currents. But the extra sea level rise from ice sheets will exacerbate the rise caused by the expansion of oceans as the world warms.” See http://oceans.pmel.noaa.gov/ where heat content prior to 2003 is unreliable.
George, you cite the Guardian comparing ice shelves to a cork in a bottle “jamming the flow of ice from the massive ice sheets of east and west Antarctica”. This is not true except maybe for a few places e.g. along the Antarctic Peninsula where sea ice is trapped in fjords, by islands and shoals. In most places around Antarctica ice shelves are free floating with a maximum thickness of 200-300 m and are pushed out by glaciers flowing to sea; a completely natural process due to the viscous fluid nature of ice under pressure.
Headlines insisting that the ice of Antarctica is dramatically breaking up in huge icebergs is an indication of global warming is utter nonsense. Imagine what would happen if ice would continue accumulating in thickness due to continuous snowfall on Antarctica and no seaward flow would occur. Fortunately glaciers flow down slope towards the ocean thinning out due to gravitational pressure and internal structural collapse to an average thickness of 200-300 m. reaching the open ocean. Where this ice sheet loses contact with the sea floor (the grounding line on the continental shelf) continuous flexing due to tidal up and down motion, the ice shelf will break up and form huge icebergs. This is a completely logical, natural process with no connection to assumed global warming.
Furthermore, the final disintegration of a floating ice shelf or ice bergs for that matter will not increase sea level.
Your main question about sea level rise caused by assumed melting of glaciers on Antarctica will be visible in the Mediterranean Sea was partly answered by Sönke based on crustal far field effect. However, considering sea level fluctuations thru recent geological history, during the last ice age with extensive accumulation of ice in polar and subpolar regions, global sea levels dropped by 120-130 meters below current levels. With the melting of the massive continental ice sheets sea level rose during the past 12-13,000 years back to its present level, partly adjusted by isostatic crustal movements.
Coming back to the original question whether loss of ice on Antarctica will influence the Mediterranean Sea in the foreseeable future we have to consider our planet as an entity including plate tectonics, the entire hydrographic cycle and above all natural climate variability and preferably forget about greenhouse gases.
Dear George,
If we assume that there will be sea level rise due to loss of ice from Antarctica, then there will of course be an increase in global sea level (eustasy) due to the rapid rate of dispersion of water across all joined water bodies. At the Strait of Gibraltar the Mediteranean Sea is open to the same body of water as the Southern Ocean, so it too must rise. However, due to isostasy as Antarctica loses the mass of its ice, Antarctica (particularly the deglaciating edges) will rise relative to all other continents and its percieved rate of sea level rise will be less than that for the Mediterranean Sea (which has no ice mass to lose) and Antarctica will continue to rise slowly for millennia as asthenosphere moves in laterally from the southern side of the surrounding mid ocean ridge. Isostasy is slower than eustasy, so the sea level change for Antarctica will initially rise, then reduce in rate as isostasy ramps up and sea levels around Antarctica will even reverse once the ice ceases to melt (or all of it is gone). If Antarctica loses all its ice then sea level globally (including the Mediteranean Sea) should rise 70m (+6m if Greenland loses all its ice). However, due to isostasy, Antarctica (land) will rise by ~1/3 of the height of the ice it loses (due to loss of mass). Since there is ~1-3km of ice depth to lose Antarctica will rise ~300-1000m over millennia and will effectively experience sea level decline of ~~230-900m. See "Anthropogenic Earth-Change: We are on a Slippery Slope, Breaking New Ground and It’s Our Fault—A Multi-Disciplinary Review and New Unified Earth-System Hypothesis" https://www.researchgate.net/profile/C_Allen2/contributions?ev=prf_act
Of course it will, like all other seas. But what has happened so far is that warmer waters have resulted in the evaporated water going into the air as humidity, affecting previously "dry" places like parts of Canada and previously "humid"places into "super humid" ones , like the eastern seaboard of North America.
Dear George,
obviously, it will. Global sea level can be undesrtood as a huge bathtub, in some ways. If you add water, wherever you do it, sea level will rise. Any melting in Antarctica will involve sea level rises all over the world.
On the other hand, the ranges of this rise are not the same everywhere. Due to important changes in currents and air masses, sea level is rising extremely fast in Eastern Asia (1 cm / year), in comparison with the American Pacific coast, where it has been more or less stable in the last decades. You can check it in any of the figures of Topex-Poseidon or Jason1-2 maps, like this one: http://goo.gl/JjbBIC
In fact, there are very interesting workd about Westerm Antartica melting (Mitrovica 2009, I think). They have published that a melting in this area will mean a change in the geoid, so the sea surface might be affected by this event. Nevertheless, it seems to be a small change of less than 1 mm / year: http://goo.gl/25C3pq
Anyway, there is a strong scientifc consensus around this topic: sea level will rise all over the world in 21st and 22nd centuries. Even if we leave the Earth and move to the Moon, sea level will ve rising for this period.
There is a rapid global response to any sea level rise via gravity waves. The signal propagates globally within a week or two. There is a modelling study demonstrating this effect:
20. Lorbacher, K., S.J. Marsland, J. A. Church, S. M. Griffies, and D. Stammer, 2012: Rapid barotropic sea level rise from ice sheet melting, J. Geophys. Res., 117, C06003, doi:10.1029/2011JC007733.
Dear George,
Melting of Antarctic ice will increase the global volume of ocean water. Since this is a slow process (takes hundreds of years), no straight will be a barrier for global equilibration of sea level. All depends on the share of Antarctic ice that will melt. If (as Allen said) total melting results in 70 meter rise, 1% will result in 70 cm rise (while I heard about 64 m, which is close), also in Mediterranean. The effect of rising Antarctic will be small addition to the share of continents in the earth surface area and can be neglected in this estimation. The differences of order 1 cm in equilibrium sea level across continents (mentioned by Pablo) can also be neglected when global rise will become dangerous (of order 1 m).
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