Antarctic ice cores have yielded yet more clues about the history of the atmosphere, this time for a sulfur compound that acts not only to cool the earth but also to destroy ozone. The gas is carbonyl sulfide, the most abundant sulfurous gas in the atmosphere, one that is produced naturally as well as by industrial processes. By crushing ice cores having ages from 385 to 310 years old, Murat Aydin and colleagues have reported that the air trapped in the ice during the 1600s held only three-fourths as much carbonyl sulfide as the present atmosphere does. They infer that industrial emissions may be responsible for one-fourth of the current amounts of this gas.

Murat Aydin's work appeared in Geophysical Research Letters, v. 29, 15 May 2002.¹

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Another morsel in the stew of carbon sequestration: Ground- based studies suggested that tropical forests were absorbing more CO₂ from the air than deforestation elsewhere was releasing into the air. However, a new study by Jeffrey Richey and co-workers has identified a new source of CO₂: outgassing from rivers and wetlands. It appears that rivers transport a load of organic debris from upland forests, which is then decomposed in the rivers, thus releasing CO₂ into the air. The authors suggest that the overall budget of carbon in rain forests is closer to balance than earlier studies had suggested.

Their report appears in Nature, v. 417, 617-620, April 2002; online at www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v416/n6881/full/416617a_fs.html

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Certain human activities offset a healthy part of the emissions of greenhouse gases from other activities. Planting and growth of new trees and vegetation absorbs or "sequesters" CO₂, converting it into wood, vegetation and organic matter. As long as more vegetation is created than destroyed during a time period, then CO₂ is removed from the atmosphere. Deforestation, then, enhances the greenhouse effect by adding CO₂, while "afforestation" can be one viable solution to greenhouse effects, and is part of the climate policies of many nations, including the US. The US land mass has been absorbing more CO₂ through the years, with a 14% increase in total vegetation over some 43 years, but the reasons have not been clear. A simple explanation comes from R. Nemani and co-workers at the School of Forestry of the University of Montana, who found that increases in rainfall may account for two-thirds of the increase in vegetation growth. Although the explanation is simple, it has been overlooked.

The study appeared in the Geophysical Research Letters of 28 May 2002. ¹

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Although many climate indices exhibit a trend when their average is computed over a long period of time, Vinnikov and Robock (2002) report that the so-called variance of five common indices did not show any trends at all. The variance or the standard deviation are used to measure the variability of climate. The five indices are:

-- Average sea level at New York City rose 30 cm (one foot) in 100 years, but its year-to-year variability remained the same.
-- U.S. mean annual precipitation increased about 8% over 100 years, which was statistically significant, but its variability did not change appreciably.
-- The other three indices showed no change in the average and also no change in variability: (a) the Palmer Drought Index, (b) the strength of the Indian Monsoon, and (c) El Niño.

Their work, "Trends in moments of climatic indices" appeared in Geophysical Research Letters, v. 29, 14-1, on 29 Jan 2002.<sup>1

1</sup> www.agu.org/pubs/toc2002/gl.shtml

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