What was done
The authors, in their words, "analyzed diatom samples from glacial meltwater streams in the McMurdo Dry Valleys, the largest ice-free area in Antarctica," which they describe as "one of the most extreme environments on earth." This they did because, as they describe it, "a cooling trend is documented in the Dry Valleys between 1986 and 2000 (Doran et al., 2002), continuing at least to January 2005 (http://www.mcmlter.org/met_home.htm)," and because "cooling has also been widespread on the continent over the last several decades (e.g., Doran et al., 2002; Kwok and Comiso, 2002)."

What was learned
Esposito et al. found that diatoms are abundant in McMurdo Dry Valley meltwater streams, with 24 of the streams' 40 species having only been found in Antarctica. Furthermore, they determined that "decreased solar radiation and air-temperatures reduce annual stream flow, raising the dominance of these Antarctic species to levels above 60%." Hence, they conclude that "cooling favors the Antarctic species" but that it ultimately "lowers diatom species diversity in this region."

What it means
In the Conclusions section of their paper, the eight U.S. researchers say that "recent Dry Valley cooling trends (Torinesi et al., 2003; Doran et al., 2002) have the potential to alter the diatom populations," and that "under cooler, cloudier summer conditions, a higher abundance of Antarctic species would be expected to lower overall diatom diversity." In a rare twist of irony, however, they note that this unfortunate trend "may be reversed if warming were to occur, as predicted by Shindell and Schmidt (2004)." As not much has happened in this regard, however, perhaps we should pray for a bit more global warming, especially in earth's southern polar region, to avert this impending catastrophe. Or, if we feel our faith is insufficient to invoke the help of Deity in the matter, perhaps we should rely on our own insight and prowess, and pump more CO2 into the air. Surely that will help; the climate-model oracles have decreed it.

References
Doran, P.T., Priscu, J.C., Lyons, W.B., Walsh, J.E., Fountain, A.G., McKnight, D.M., Moorhead, D.L., Virginia, R.A., Wall, D.H., Clow, G.D., Fritsen, C.H., McKay, C.P. and Parsons, A.N. 2002. Antarctic climate cooling and terrestrial ecosystem response. Nature 415: 517-520.

Kwok, R. and Comiso, J.C. 2002. Southern Ocean climate and sea ice anomalies associated with the Southern Oscillation. Journal of Climate 15: 487-501.

Shindell, D.T. and Schmidt, G.A. 2004. Southern hemisphere climate response to ozone changes and greenhouse gas increases. Geophysical Research Letters 31: 10.1029/2004GL020724.

Torinesi, O., Fily, M. and Genthion, C. 2003. Variability and trends of the summer melt period of Antarctic ice margins since 1980 from microwave sensors. Journal of Climate 16: 1047-1060.