The only reference I can find to answer your question is as follows
"Melting ice in Antarctica produced global sea level rises of 0.4
mm/year between 2002 and 2005, according to a new study published
March 2, 2006 in the on-line journal Science Express. The study,
titled "Measurements of Time-Variable Gravity Show Mass Loss in
Antarctica", by University of Colorado researchers Isabella Velicogna
and John Wahr, used satellite data from two NASA satellites called the
Gravity Recovery and Climate Experiment (GRACE). The satellites
measured the changing pull of gravity from the two large ice sheets
covering Antarctica to determine how much ice was on the continent,
and how fast the ice was changing. Most of the melting discovered was
from the West Antarctic Ice Sheet. This is the smaller of the two ice
sheets covering Antarctica, and holds enough ice to raise global sea
levels 20 feet should it completely melt. The rock on which the West
Antarctic ice rests is below sea level, and the sheet could be melting
on its underside due to warming ocean waters penetrating there and
melting it from both below and along the edges. The study found little
melting of the huge East Antarctic Ice Sheet (which would raise global
sea levels 200 feet if it were to melt). This ice sheet is on rock
high above sea level, so warmer ocean waters cannot affect it.
Additionally, the East Antarctic Ice Sheet has average temperatures so
cold that even a 5-10C increase in temperatures is not expected to
seriously threaten it.
The net Antarctic melting reported comes as a surprise, since the
"official" prediction from the latest 2001 report from the
Intergovernmental Panel on Climate Change is that global warming
should cause increased precipitation over Antarctica this century.
This increased precipitation is expected to exceed Antarctica's
melting enough to decrease global sea level. This decrease in sea
level by 2100 is predicted to be about 3 inches (8 cm), ± 4 inches (10
cm), but would be offset by increases in sea level due to thermal
expansion of the seas due to warmer water temperatures, plus melting
of Greenland and glaciers on other continents.
As I reported in my blog on Greenland's greenhouse, total global sea
level rise in recent years has been between 1.5 and 2.9 mm/year. Thus,
the .4 mm/year contribution from Antarctica found by the new study
represents a significant portion of this rise. However, another study
published in December 2005 in the Journal of Glaciology titled, "Mass
changes of the Greenland and Antarctic ice sheets and shelves and
contributions to sea-level rise: 1992-2002" found a rate of melting
for Antarctica five times smaller, for the earlier period 1992-2002.
This research, performed by a team led by NASA scientist H. Jay
Zwally, used satellite radar altimetry data from the European
Remote-sensing Satellites ERS-1 and -2, and found a net melting of
only .08 mm/year from Antarctica. Did Antarctica's melting really
increase 5-fold in past three years? If so, is this a short term
fluctuation, or indication of a long term trend? I'm of the opinion
that's it's too soon to tell. It is extremely difficult to do mass
balance studies of these huge ice sheets, since it requires finding a
small change in a very large number. The same problem affects the
recent estimates of Greenland's mass balance. The new study from the
Journal of Glaciology also reported that between 1992 and 2002, the
total mass of the Greenland Ice Sheet increased and thus Greenland
caused a .03 mm/year decrease in sea level. This result is in
contradiction to the two studies I quoted in my Greenland blog, by Box
et al. (2004), who found that Greenland contributed to a net increase
in global sea level of 1.5 mm/year, and Rignot et al. (2006), who
found a .23 mm/year rise for the year 1996, increasing to .57 mm/year
by 2005. I'd like to see at least three to five more years of
satellite measurements before concluding that Antarctica or Greenland
are undergoing significant melting. The European Space Agency is
launching a satellite called CryoSat in March 2009 that should help
answer these questions. If you want a more technical discussion of the
issues, realclimate.org published a nice analysis last week.
Coverage in the press
It was interesting to watch the reaction of the press to the release
of the new study. The New York Times titled their article, "Loss of
Antarctic Ice Increases", and did a reasonable job covering some of
the uncertainties. The USA Today was a bit more alarmist, headlining
their article, "Study: Antarctic ice sheet in 'significant decline'".
The Washington Post had a very alarmist title to their article,
"Antarctic Ice Sheet Is Melting Rapidly". The facts and uncertainties
involved in the making ice sheet balance measurements do not support
this claim, as of now. Although any news of an increase in melting
from Antarctica or Greenland is worthy of concern, I thought that in
general, the media's headlines on the matter were too alarmist, given
the uncertainties involved.
My next blog will be Thursday, when perhaps I'll be able to talk about
Phoenix's first rain in 142 days. They've got a 20% chance of rain on
Wednesday!
Jeff Masters
References
Box, J.E., D.H. Bromwich, and L-S Bai, 2004. Greenland ice sheet
surface mass balance 1991-2000: Application of Polar MM5 mesoscale
model and in situ data. J. Geophys. Res., 109, D16105,
doi:10.1029/2003JD004451.
Rignot, E., and P. Kanagaratnam, "Changes in the Velocity Structure of
the Greenland Ice Sheet" Science 311, 986-990, 17 February 2006, DOI:
10.1126/science.1121381 "
This is from the following website.
http://64.233.183.104/search?q=cache:BQeWThd1gHYJ:www.wunderground.com/blog/JeffMasters/comment.html%3Fentrynum%3D314%26tstamp%3D200603+will+melting+of+ice+change+earth+tilt&hl=en&gl=uk&ct=clnk&cd=5
--Keystroke-ga |
