[Vision2020] Antarctica Ice Mass Decrease: GRACE Satellites: Gravity Recovery and Climate Experiment

[Ted Moffett]

Another common argument heard over and over from the anthropogenic warming
is doubtful camp refers to the fact that Antarctica sea ice is increasing,
so how can this be happening if there is climate warming?  Yes, for complex
reasons, Antarctica sea ice is increasing; but much of the ice mass at the
South Pole is land ice on the continent, not sea ice; and satellite
measurements from GRACE indicate a loss of total ice mass in Antarctica.
GRACE is an amazing pair of satellites, making measurements that seem
impossible... Oh wait, maybe they are, given it's a gov'mint NASA operation
run by those hoax perpetrating global warmers...

http://www.csr.utexas.edu/grace/

  GRACE in the News <http://www.csr.utexas.edu/grace/publications/press/>

*GRACE: Tracking Water from
Space<http://sciencebulletins.amnh.org/?sid=e.f.GRACE.20090717&src=l>
*

<http://sciencebulletins.amnh.org/?sid=e.f.GRACE.20090717&src=l>NASA's
Gravity and Climate Experiment (GRACE) is an audacious mission to track the
impact of climate change on the planet's vast tracts of freshwater,
saltwater, and ice. GRACE's pair of satellites responds to the gravitational
pull of these massive stores, effectively "weighing" Earth's shifting water
resources month by month. The satellites can detect where water is
accumulating and drying up on a grand scale data that were unavailable
before. GRACE's unprecedented view of our water planet could prove critical
in the effort to anticipate and manage the consequences of climate change
for people worldwide.

-------------------------
A published science article on GRACE measurements of Antarctic ice mass is
referenced below, followed by a discussion of this issue from
skepticalscience.com:

http://www.agu.org/pubs/crossref/2008/2007JF000871.shtml

 Antarctic ice mass balance estimates from GRACE: Tidal aliasing effects

Philip Moore

School of Civil Engineering and Geosciences, Newcastle University, Newcastle
upon Tyne, UK

Matt A. King

School of Civil Engineering and Geosciences, Newcastle University, Newcastle
upon Tyne, UK

Geophysical interpretation of GRACE gravity fields has provided estimates of
Antarctic ice mass change. Such analyses rely on proper consideration of
ocean tidal effects through the models CSR4 and FES2004. In general,
mis-modeling of tidal constituents with aliasing period less than 30 day
will not have significant impact on ice mass change. However, for
constituents, such as K1, K2, and S2, the aliasing period is sufficiently
large to potentially compromise long-term variability studies. Here we
quantify tidal aliasing over Antarctica by simulating GRACE signatures due
to differences between CSR4 and FES2004, and the best available
circum-Antarctic model, TPXO6.2. The S2 simulations are in close agreement
with the observed S2 signal from GRACE. Simulations of ice mass change show
that over 2002–2006 long-term K1 and K2 aliasing is equivalent to a rate
error of 4.5 ± 1.3 km3/a of ice with CSR4, but only 0.2 ± 0.2 km3/a with
FES2004. After spatial averaging and destriping, K1 plus K2 mis-modeling in
CSR4 (FES2004) introduce point-wise errors up to 5 (2) mm/a in equivalent
water height over a 3.5 year period. With observed mass change equivalent to
less than 30 mm/a of water height over much of Antarctica, the simulations
show tidal aliasing uncertainty at the 2–3 mm/a level for August
2002–January 2006, or ∼10% of the signal. With GRACE Release 04, the revised
estimate (April 2002–January 2006) of published ice volume decrease is 164 ±
80 km3/a of ice, although this value depends very much on the GIA model and
GRACE analysis approach.

Received 11 July 2007; accepted 27 December 2007; published 10 April 2008.

*Citation: *Moore, P., and M. A. King (2008), Antarctic ice mass balance
estimates from GRACE: Tidal aliasing effects, *J. Geophys. Res.*, 113,
F02005, doi:10.1029/2007JF000871.
-------------------------
http://www.skepticalscience.com/antarctica-gaining-ice.htm
 Is Antarctica losing or gaining ice? The skeptic argument...

The amount of ice surrounding Antarctica is now at the highest level ever
measured for this time of the year, since satellites first began to monitor
it almost 30 years ago. All of the IPCC’s models of Antarctica in the
twenty-first century forecast a gain in ice, as a warmer surrounding ocean
evaporates more water, which subsequently falls in the form of snow when it
hits the continent. Other studies, such as Peter Doran’s in Nature in 2003,
show actual cooling in recent decades. It’s simply too cold for rain in
Antarctica, and it’ll stay that way for a very long time. The bottom line is
that there is more ice than ever surrounding Antarctica (source: Patrick
Michaels <http://www.mywebtimes.com/bloggers/blitz/?p=27>).
What the science says...

Overall, Antarctic land ice is falling. Antarctic sea ice is growing *
despite* a warming Southern Ocean.

It's important to distinguish between Antarctic land ice and sea ice which
are two separate phenomenon.
Antarctic Land Ice

Measuring changes in Antarctic land ice mass has been a difficult process
due to the ice sheet's size and complexity. However, over the last few
years, the Gravity Recovery and Climate Experiment (GRACE) satellites have
been able to comprehensively survey the entire ice sheet. Using measurements
of time-variable gravity, Velicogna
2007<http://www.sciencemag.org/cgi/content/abstract/311/5768/1754>determined
mass variations
of the entire Antarctic ice sheet from 2002 to 2005. They found the overall
mass of the ice sheet decreased significantly, at a rate of 152 ± 80 cubic
kilometers of ice per year (equivalent to 0.4 ± 0.2 millimeters of
global sea-level
rise per year). Most of this mass loss came from the West Antarctic Ice
Sheet. Figure 1 displays Antarctica's ice mass from 2002 to 2005 - the red
crosses is their best estimate with the dotted line the linear trend.


*Figure 1: GRACE monthly mass solutions for the Antarctic ice sheet for
April 2002 to August 2005. Blue circles show results after removing the
hydrology leakage. Red crosses show results after also removing the PGR
signal. The latter represent our best estimates of mass variability. Also
shown is the linear trend that best fits the red crosses.*

Also illuminating is Figure 2 which contrasts the mass changes in West
Antarctica (red) compared to East Antarctica (green):


*Figure 2: Monthly ice mass changes and their best-fitting linear trends for
WAIS (red) and EAIS (green) for April 2002 to August 2005.*

Most of the Antarctic mass loss comes from Western Antarctica with a mass
loss of 148 ± 21 km3/year. The mass loss from East Antarctica is 0 ±
56 km3/year.
Because of its relatively large uncertainty, it's uncertain whether East
Antarctica is in mass balance or not.

Why is Western Antarctica losing ice mass while East Antarctica is
relatively steady. The hole in the ozone layer above the South Pole
causes cooling
in the stratosphere<http://www.sciencemag.org/cgi/content/abstract/302/5643/273>.
This increases circular winds around the continent preventing warmer air
from reaching east Antarctica and the Antarctic
plateau<http://www.sciencemag.org/cgi/content/abstract/296/5569/895>.
The flip side of this is the Antarctic Peninsula in Western Antarctica has
"experienced some of the fastest warming on
Earth<http://www.antarctica.ac.uk/press/press_releases/press_release.php?id=91>,
nearly 3°C over the last half-century".
Antarctic Sea Ice

Antarctic sea ice has shown long term growth since satellites began
measurements in 1979. This is an observation that has been often cited by
skeptics as proof against global warming. However, in all the skeptic
articles I've read, not one has raised the crucial question: *why* is
Antarctic sea ice increasing?


*Figure 1: annual mean sea ice extent, observed by satellite. Straight line
is the trend line (**Zhang
2007*<http://psc.apl.washington.edu/zhang/Pubs/Zhang_Antarctic_20-11-2515.pdf>
*).*

The implicit assumption is that if Antarctic sea ice is growing, it must be
cooling around Antarctica. This is decidely not the case. In fact, the
Southern Ocean has been warming faster than other oceans in the world. The
average global ocean temperature trend has been 0.1°C per decade from 1955
to 1995. In contrast, the Southern Ocean has been warming at 0.17°C per
decade. Not only is the Southern Ocean warming, it is warming faster
than the global trend.


*Figure 2: Linear trend (1979–2004) of surface air temperature over the
ice-covered areas of the Southern Ocean.*

So this raises the big question: if the Southern Ocean is warming, why is
Antarctic sea ice increasing? The paper Increasing Antarctic Sea Ice under
Warming Atmospheric and Oceanic Conditions (Zhang
2007)<http://psc.apl.washington.edu/zhang/Pubs/Zhang_Antarctic_20-11-2515.pdf>
attempts
to answer this question.

The paper uses a coupled ocean/sea ice model to find the predominant reason
that sea ice is increasing is due to a decrease in upward ocean heat
transport. Eg - less heat is being carried up by ocean convection to melt
sea ice. The reason for this is a complex chain of events.

When surface temperature increases, the upper ocean warms and ice growth
decreases. This leads to a decrease in salt rejection from new ice. The
salinity of the upper ocean falls. Lower salinity and warmer water results
in lower water density in the upper ocean. With fresher, less dense upper
water, there is now increased stratification of ocean layers which weakens
convective overturning. Less ocean heat is transported upwards. This leads
to a decrease in ice melting from ocean heat. Hence we observe an increase
in net ice production - sea ice increases.

While all that is a bit of a mouthful, it's actually a simplification of the
process as there are various feedbacks along the process. Warming air
increases upper ocean temperature which affects air temperature through
air-sea interactions. Warming temperature leads to increased precipitation
which increases sea ice growth. More sea ice means less atmospheric heat can
penetrate waters.

The bottom line is the answer to Antarctic sea ice isn't simple - the
Southern Ocean is a complex system with a number of factors likely
contributing. One factor certainly isn't a contributor - the simplistic
explanation that it must be cooling around Antarctica is not the case.
Warming is happening - how it affects specific areas is complicated.

  ------------------------------------------
Vision2020 Post: Ted Moffett
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.fsr.com/pipermail/vision2020/attachments/20090816/43f3a827/attachment.html