Posted on 03/03/2006 9:58:52 AM PST by Antroad
TCS Daily Antarctic Ice: The Cold Truth Font Size:
By Dr. Patrick Michaels : BIO | 03 Mar 2006
This week Science Magazine's on-line SciencExpress reports that Antarctica has been losing large amounts of ice mass over the past three years, contributing to sea level rise at a rate of 0.4 ± 0.2 mm/year. This comes on the heels of a paper published by Science two weeks ago that reported that Greenland was also losing big chunks of ice and contributing to sea level rise at a rate of 0.57 mm/yr.
If this sounds like one of those repeating news stories -- Coup in Haiti, Osama Sends a Tape, etc. -- it is. And so is the response. Natural variability is sufficiently large on yearly and multidecadal time scales that it is simply impossible to conclude that anything other than natural variability is at play in either of these two stories.
The SciencExpress paper by Isabella Velicogna and John Wahr reports on 34 months of data recorded by a new NASA satellite that measures the pull of gravity. Variations in the gravitational field are related to variations in the local mass beneath the satellite. If the mass changes, the satellite observes a different degree of gravitational pull.
Velicogna and Wahl attempted to use the gravity variations observed over Antarctica to determine whether Antarctica was gaining or losing mass. But, their analysis is complicated because variations in gravity can be caused by many things. These include variations in atmospheric pressure (the atmosphere has a certain mass); gravity signals arising from outside of Antarctica; and mass changes from a process known as post-glacial rebound -- slow, ongoing changes to the earth's crust as it adjusts to the removal of its huge ice load from the last ice age. Each of these effects needs to be correctly accounted for before estimating snow and ice changes. After this process, Velicogna and Wahr derived the time history of the variations in ice mass covering Antarctica (from April 2002 through August 2005) shown in Figure 1.
Figure 1. The variations in ice mass (in units of volume) covering Antarctica from April 2002 through August 2005. The blue points are the values uncorrected for post glacial rebound, and the red points represent the ice mass corrected for all external influences. The dashed black line is the trend through the corrected (red) values. (Source: Velicogna and Wahl, 2006).
Additionally, the researchers calculated the ice mass changes for the two major ice sheets across Antarctica -- the Western Antarctic Ice Sheet (WAIS) and the Eastern Antarctic Ice Sheet (EAIS) -- which together cover the vast majority of the continent. Figure 2 shows that the there is no trend in the EAIS (which is about 3 times as large as the WAIS) and that virtually all of the mass loss is coming from the WAIS.
Figure 2. The ice mass variations over the West Antarctic Ice Sheet (red) and the East Antarctic Ice Sheet (green). (Source: Velicogna and Wahl, 2006).
This differs from the results published by Davis et al. in Science magazine just last summer, which used a different satellite and over a longer time period -- May1982 through May 2003. While Davis et al. did find that the smaller WAIS was losing mass, they also found that the much larger EAIS was gaining mass at a rate that exceeded the loss over the WAIS. In total, Davis et al. found that Antarctica was gaining mass (from increased snow accumulation) and contributing to a decline in sea level of about 0.09 mm/yr. The differences between these two results likely lie somewhere in the collection of factors that include different time periods, different spatial coverages, and in analysis uncertainties.
However, one thing is clear. The beginning of the Velicogna and Wahl analysis occurs during an unusually high point in the longer record of Davis et al. (Figure 3). This means that the apparent decline in the record of Velicogna and Wahl may simply be a short term correction to an anomalously high mass gain during a period of long-term mass growth. But who is to know for sure? It is impossible to tell anything about a trend in a system as vast as Antarctica with less than three years worth of data.
Figure 3. The ice mass changes (in terms of elevations change) observed over the East Antarctic Ice Sheet by Davis et al. from May 1992-May 2003. Notice that in mid-2002 (the start of the Velicogna and Wahl analysis) ice mass was at the highest level in the record.
Records of the extent of sea ice surrounding Antarctica are available from satellite observations starting back in the late 1980s. Figure 4 (from the National Snow and Ice Data Center) shows that there has been a slight increase in sea ice during the past two decades. Floating sea ice is a different system than the one being measured by either of the two studies mentioned above. Nevertheless it gives some indication as to what is going on in the environs of the extreme Southern Hemisphere. And it certainly doesn't look like ice is disappearing (notice, however, that there is a lot of variation on the yearly to multi-yearly scale).
Figure 4. Sea ice trends around the coast of Antarctica (Source: http://nsidc.org/data/smmr_ssmi_ancillary/regions/total_antarctic.html)
So, all the Velicogan and Wahl results really demonstrate is that there are short term variations in the amount of ice and snow covering the Antarctic continent. Other data indicate that over the course of the past several decades at least, that the ocean-land system of Antarctica has been experiencing a growth in the amount of snow and ice there (Figure 5).
Figure 5. In some parts of Antarctica, such as East Antarctica, the ice sheet is thickening (+ symbols), whereas in others, primarily in West Antarctica it is thinning (– symbols). (Source: Vaughn, 2005).
There is nothing inherently noteworthy about the results of this three year study of Antarctic ice trends. This is not to disparage the scientific work of Velicogna and Wahl. It is to suggest that their paper serves more as a initial investigation into some of the applications of observations of gravitational variations, rather than bearing any relevance to the issue of global climate change and its implications.
References:
Davis, C. H., et al., 2005. Snowfall-driven growth in East Antarctic ice sheet mitigates recent sea-level rise. Science, 308, 1898-1901.
Rignot, E., and P. Kanagaratnam, 2006. Changes in the velocity structure of the Greenland ice sheet. Science, 31, 986-990.
Velicogna, I., and J. Wahr, 2006. Measurements of time-variable gravity show mass loss in Antarctica. Sciencexpress, March 2, 2006.
Vaughn, D.G., 2005. How does the Antarctic ice sheet affect sea level rise? Science, 308, 1877-1878.
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And last year it was expanding. The global warming theorists really should try to get on the same page if the expect to be taken seriously.
This comes on the heels of a paper published by Science two weeks ago that reported that Greenland was also losing big chunks of ice and contributing to sea level rise at a rate of 0.57 mm/yr.
So has anyone measured a sea level rise in New York of 1 mm???
Yeah, yeah, yeah, it gets warmer, there's more CO2, which triggers more blue green alge in the oceans, which leads to a carbon sink, and more O2 and a cooling atmosphere. Who cares?
Owl_Eagle(If what I just wrote makes you sad or angry,
Even these guys are fast enough to get away.
So this means were not doomed after all?
By stock in Alaska land companies. We may all be moving there! My point. So what if the world changes. We change with it. Americans are way too fearful for their own good. Americans from even 40 years ago would say we've turned into a bunch of risk averters. Think about it. we are constantly trying to reduce stress. Why? Stress is what got us to this stage of development.
I live about 400 ft above sea level. When do I get ocean front property?
"0.4 ± 0.2 mm/year."
Four tenths, plus or minus two tenths of a milimeter per year.
cue Chicken Little...
The zero-point of the sea, meticulously established on a small cliff on an island (The Isle of the Dead) off the southeast coast of Australia in 1841, shows that the ocean level has lowered by about 30 cm (about a foot) since 1841.
Increasing at less than a millimeter per year, it's going to take quite a while to simply re-establish the sea to its 1841 level.
Please don't use that french measurement system.
.57mm = .022 or 22/1000 of an inch.
thats right 50 yrs for a 1 inch rise
( assuming the weather doesn't change)
remember why the metric system was invented.
So a frenchman can say to his girlfriend,
baby I've got a 100mm for you tonight.
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