From a University of Leeds press release, comes this scary headline that seems to be picked up by the MSM. A Google search yields 16,400 hits on the title below.
Melting icebergs causing sea level rise
(Note: Be sure to see the reality punch line at the end of the article)
Scientists have discovered that changes in the amount of ice floating in the polar oceans are causing sea levels to rise.
The research, published this week in Geophysical Research Letters, is the first assessment of how quickly floating ice is being lost today.
According to Archimedes’ principle, any floating object displaces its own weight of fluid. For example, an ice cube in a glass of water does not cause the glass to overflow as it melts.
But because sea water is warmer and more salty than floating ice, changes in the amount of this ice are having an effect on global sea levels.
The loss of floating ice is equivalent to 1.5 million Titanic-sized icebergs each year. However, the study shows that spread across the global oceans, recent losses of floating ice amount to a sea level rise of just 49 micrometers per year – about a hair’s breadth.
According to lead author Professor Andrew Shepherd, of the University of Leeds, it would be unwise to discount this signal. “Over recent decades there have been dramatic reductions in the quantity of Earth’s floating ice, including collapses of Antarctic ice shelves and the retreat of Arctic sea ice,” said Prof Shepherd.
“These changes have had major impacts on regional climate and, because oceans are expected to warm considerably over the course of the 21st century, the melting of floating ice should be considered in future assessments of sea level rise.”
Professor Shepherd and his team used a combination of satellite observations and a computer model to make their assessment. They looked at changes in the area and thickness of sea ice and ice shelves, and found that the overall signal amounts to a 742 cubic kilometres per year reduction in the volume of floating.
Because of differences in the density and temperature of ice and sea water, the net effect is to increase sea level by 2.6% of this volume, equivalent to 49 micrometers per year spread across the global oceans.
The greatest losses were due to the rapid retreat of Arctic Sea ice and to the collapse and thinning of ice shelves at the Antarctic Peninsula and in the Amundsen Sea.
For more information
To arrange an interview with Prof Andy Shepherd, contact Hannah Isom in the University of Leeds press office on 0113 343 4031 or email h.isom@leeds.ac.uk
Notes to editors
“Recent loss of floating ice and the consequent sea level contribution” by Andrew Shepherd, Duncan Wingham, David Wallis, Katharine Giles, Seymour Laxon, and Aud Venke Sundal is published this week in Geophysical Research Letters (doi:10.1029/2010GL042496).
ICE SHELVES are thick, floating platforms of ice that form where a glacier or ice sheet flows down to a coastline and onto the ocean surface. Ice shelves are found mainly in Antarctica , and range from about 100 to 1000 metres in thickness.
SEA ICE is formed on the surface of sea water as the ocean freezes, and is typically less than 3 metres in thickness. It is found extensively in both the Arctic and Antarctic regions, and it’s extent varies considerably over the seasons.
This study was funded by the UK National Centre for Earth Observation and the Philip Leverhulme Trust.
==========================================
OK here’s the reality punch line:
Assuming their theory of 49 micrometers per year rise (this conversion equals 0.0019 inch or 0.00016 feet ) due to the differences is salty and fresh water holds true, then we can assess the threat level.
At this rate, to see an inch of sea level rise from melting icebergs we’d need:
1 inch/0.0019 inch/yr = 526 years
Yeah, I’m worried about that.
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OK I confess, not done real physics for , well many years. but if i’ve got x megatons of ice floating in the oggin they’ll displace x megatons of water, when it melts to x megatons of water and stops displacing the same mass shouldn’t it even out? In fact as the density of water is highest at 4C shouldn’t it fall in volume until it warms significantly above that point?
Of course, “recent” “floating ice” is only “recent” “floating ice.” Not the totality of floating ice. And not the much larger amount of ice sitting on top of land that, if melted, would increase sea level by meters.
So either the blogger is completely ignorant or is intentionally trying to misrepresent the information.
Or, of course, both.
wayne says:
May 1, 2010 at 8:28 am
Ron Manley says:
May 1, 2010 at 8:31 am
jaymam says:
May 1, 2010 at 5:42 pm
“Charles Higley, surely you don’t believe that Professor Andrew Shepherd would write an article with such an error of basic physics”.
“That is true if ice is floating in pure water, since the mass of water displaced will be the exact same volume as the water it becomes. If the ice is floating in a heavier medium, such as salt water, the volume of water it melts into is more than the volume of sea water it displaced as ice”.
Yes, in an experiment where we have fresh water ice floating in salt water done in isolation to what actually takes place. All sea ice began as frozen salt water and over time loses the salt to become fresh water. To suggest that when this same frozen water is melted we have a rise in sea level means somehow we end up with more water than we started with.
One should run this experiment over several cycles of freezing and melting and using a single source of salt water.
I wonder how much all the sediment from rivers
& other sources raise sea level?
Stephen Skinner says:
May 3, 2010 at 2:48 pm
wayne says:
May 1, 2010 at 8:28 am
Ron Manley says:
May 1, 2010 at 8:31 am
jaymam says:
May 1, 2010 at 5:42 pm
I concede that if all the sea ice melted there would be a rise in sea level. I was looking at it from a starting point of unfrozen sea water and of course in the case of the Arctic it is never completely unfrozen. However Jaymen’s point that any such rise is negligable should be stated which I suppose it is with “49 micrometers per year”. I still find this level of accuracy interesting though. Why not make it a round 50 micrometers?
I’ve done the experiment with a test tube containing salt water with an equal volume of pure ice floating in it. When the ice melts the level rises about 2.5% (by 11 pixels over 441 pixels).
http://i43.tinypic.com/2dhsbyb.jpg
I was going to do it again more carefully but I think this is good enough for me.
The final conclusion should be:- if lots of sea ice melts, there will be a global sea level rise of a few thousandths of an inch. When new sea ice is created each year the sea level will drop again.