How might processes like ocean and atmospheric warming cause mass loss from calving to increase? What do you think are the key controlling processes?
There is some really interesting reading about this subject. The dominant discussion seems to be in the effects of a warming ocean. Greenland and the Western Antarctic Ice Sheet come up frequently as the two main ice sheets that Glaciologists are concerned about. Greenland is warmer, in general, than the Southern polar region, so may be more sensitive to change. Below are some examples of how the ice sheets are being affected, and ways in which calving rates could increase.
Thermal Expansion. In the past one of the major factors affecting sea level rise has been through thermal expansion of the oceans. This is still true, but as global temperatures rise this will be reflected in ever rising sea levels.
Ice-shelves. These are the ice sheets that extend over the ocean. It's the first line of defence and the area where calving happens most frequently. As the sea temperatures rise, the ice shelves are warmed from underneath. This would cause them to break up more readily. Large icebergs would form and drift out to sea. However, the water trapped in the ice shelves is already accounted for in sea level measurements, so these events would not really cause any rise. The danger comes because some of these ice shelves act as buttresses to greater quantities of inland ice. If this inland ice was left unsupported it could flow to the edge of the oceans, calve away and contribute to sea level rises. There are particular fears of this in the Western Antarctic Ice Sheet.
Precipitation: A warmer climate encourages the uptake of water vapour into the atmosphere, which then falls as precipitation. Snow, in the polar regions. The three reasons behind this are 1. Warmer air can carry more moisture; 2. Warmer waters means more evaporation; 3. Reduced sea ice means more of the ocean is uncovered, so, again, more evaporation. This would, seemingly, lead to an increase in ice cover... However observations seem to be showing that the balance is in favour of the loss of ice cover.
Basal lubrication. There seem to be conflicting and changing discussions around this issue. A study, using computer models based on observations during fieldwork in Greenland from The University of Bristol revealed that by the year 2200 lubrication would only add a maximum of 8mm for that year to sea-level rise – less than 5% of the total projected contribution from the Greenland ice sheet.
Lead author, Dr Sarah Shannon, from the University of Bristol, says,
“This is an important step forward in our understanding of the factors that control sea-level rise from the Greenland Ice Sheet. Our results show that melt-water enhanced lubrication will have a minor contribution to future sea-level rise. Future mass loss will be governed by changes in surface melt-water runoff or iceberg calving.”
“We found that the melt-water would lead to a redistribution of the ice, but not necessarily to an increase in flow.”
Antarctica’s ice sheet has been called the ‘sleeping giant’ of sea level, but it’s beginning to stir. Everything we've seen about this change points to human influences on climate – and now we’re at the point where human actions will be needed to stop it. - Dr Ted Scambos
Refs
http://www.aip.org/history/climate/floods.htm
http://earthobservatory.nasa.gov/Features/PolarIce/polar_ice2.php
http://www.theguardian.com/environment/climate-consensus-97-per-cent/2014/may/30/global-warming-vulnerability-greenlands-ice-sheet
http://www.nature.com/articles/ngeo2167.epdf?referrer_access_token=L-oQy7WT-LAYYF8pZ4wR9tRgN0jAjWel9jnR3ZoTv0Pf_LUEqgO1ubFbW_Fvq0s81-HZKnVEK146NaEKgjYtU12w1TH8UO27_Yo_2CBKt-I%3D
http://www.theguardian.com/environment/climate-consensus-97-per-cent/2015/jan/14/antarctic-ice-sheet-a-sleeping-giant-beginning-to-stir
http://www.ice2sea.eu/2013/08/12/pr2013_09/
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