Sulfur-climate link called insignificant.

Sulfur-climate link called insignificant

People have speculated that gaseous sulfur produced by one-celled marine plants might help counter human-induced global warming. The idea emerged after researchers suggested last year that these emissions might partially regulate Earth's temperature (SN: 12/5/87, p.362). Then an August 1988 report suggested the gas from plankton might actually intensify the greenhouse effect. Now chemist Steven E. Schwartz says the plankton probably don't play any role in controlling global temperature.

Moreover, in the Dec. 1 NATURE, Schwartz contends gaseous sulfur in general does not significantly influence global temperature. He says comparing historical temperature trends with recent atmospheric-sulfur measurements shows that sulfur dioxide from fossil-fuel burning, the single largest source of gaseous atmospheric sulfur, has not controlled world temperature. Therefore, Schwartz says, neither plankton-produced dimethylsulfide nor any other gaseous sulfur compound is affecting greenhouse warming. Fossil-fuel combustion accounts for about half the sulfur gas released into the atmosphere, while dimethylsulfide from plankton amounts to less than one-fourth, he adds.

Schwartz, of Brookhaven National Laboratory in Upton, N.Y., says that even though most fossil-fuel burning occurs north of the equator, average temperature trends have varied little across that boundary. "It looks like the Northern Hemisphere has 1-1/2 times as much sulfur aerosol as the Southern Hemisphere, but average temperature in both hemispheres has increased the same amount -- 0.5[deg.]C to 0.6[deg.]C -- during the past 100 years," he says. "We're left with a puzzle: Why isn't the Earth responding to the difference in these emissions?"

Robert J. Charlson of the University of Washington in Seattle, one of four scientists who proposed the plankton-climate connection in the April 16, 1987, NATURE, reported with two co-workers in the Aug. 4, 1988, NATURE a test of the theory. The results suggest that if plankton emissions react at all to global warming, they might enhance it.

Charlson does not believe Schwartz's study rules out a plankton-climate connection. He says the only way to test for such a link is to examine individually each hypothesized step. First, he says, dimethylsulfide emissions would increase the concentration of cloud-forming particles; next, those particles would make clouds whiter; finally, whiter clouds would change world temperature. Schwartz says the first two steps seem reasonable but could exert local, rather than global, influences.