For years, many climatologists have been predicting that world temperatures will rise because of atmospheric buildup of greenhouse gases released by human activities. Indeed, over the past few decades, average global temperatures have been rising, by 0.19 °C per decade, but this rise has not occurred everywhere. One important exception appears to be in Antarctica, where recently, Peter Doran of the University of Illinois at Chicago, and a team of scientists, report finding a marked decrease in temperature—as much as 0.7 °C per decade since 1966.

The researchers’ findings are based on measurements obtained from in-place meteorological stations at various Antarctic locations. The collected data contradict the predictions of climate models, which indicate that as a result of greenhouse gas buildup, there should be a warming trend in the southern polar region. The observed cooling, the scientists say, challenges models of climate and ecosystem change.

Although Doran and co-workers believe that the observed cooling trend is associated with decreased wind flow over the areas that were studied, they are unsure what may have caused wind velocity to decrease. In addition, the data provide no clues about whether the observed cooling trend is likely to continue in the future.

What is certain is that the declining temperatures are having a pronounced effect on terrestrial ecosystems in dry valley areas in Antarctica. The scientists report that primary productivity of lakes in these regions is reduced by 6–9%, and soil invertebrates are declining by more than 10% annually. (Nature, January 13, 2002, 10.1038/nature710).

... and the Antarctic ice sheet is growing

Creating yet another challenge for global climate change modelers to consider, scientists report that the West Antarctic Ice Sheet is not thinning as previously believed, but is instead growing thicker. This finding, suggest Ian Joughin of the California Institute of Technology and Slawek Tulaczyk of the University of California—Santa Cruz, may indicate an end to the Holocene retreat of the region’s Ross Ice Streams.

Although previously reported analyses of ice thickness indicate a long-term, ice-thinning trend, those results, the two scientists explain, were based on limited, in situ measurements of ice flow velocity. In contrast, Joughin and Tulaczyk’s analysis takes advantage of the much-expanded database available from ice-flow velocity measurements obtained using Interferometric Synthetic Aperture Radar.

The new data, which provide the best assessment yet of the mass balance of the Ross Ice Streams, indicate the ice sheet is growing by 26.8 gigatons annually, in contrast to older estimates that there has been an ice mass shrinkage of 20.9 gigatons annually. The researchers say that stagnation of some of the region’s ice stream flows is the primary contributor to the ice buildup.

There are, however, numerous uncertainties. Most notably, the ice flow in the region of the West Antarctic Ice Sheet is extremely complex, and the data that have been obtained so far do not suggest clearly how the ice sheet will evolve over the next few centuries. Although the thickening could in fact be a decadal-scale fluctuation, Joughin and Tulaczyk contend that current thermodynamic models and data suggest ice stream flow could continue to slow, and possibly even stagnate, leading to further ice buildup. (Science 2002, 295, 476–480). —WALTER SHAUB