When less is more

In Antarctic Ice: The Cold Truth, at Tech Central Station, Dr. Patrick Michaels tells us that those trumpeting Science magazine’s recent article about Antarctic ice
disappearing as evidence of Global Warming should chill out.

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 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.

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.

The whole thing is linked above and includes some interesting graph and charts.