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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

FROM VOLUME 12, NUMBER 5, MAY 1999

JOURNAL ARTICLES...
OF GENERAL INTEREST

Item #d99may1

Geochemical Consequences of Increased Atmospheric Carbon Dioxide on Coral Reefs,” J. A. Kleypas et al., Science, 284 (5411), 118-120 (1999).

A coral reef is the accumulation of calcium carbonate produced by corals and other calcium-secreting organisms, such as coralline algae. If calcium production declines, coral and algal skeletons weaken and reef building may slow or stop. The reef then becomes more vulnerable to erosion. As CO₂ dissolves in seawater, it produces an acid that lowers the seawater pH, in turn decreasing the level of calcium carbonate saturation. Laboratory experiments indicate that coral and algal calcification declines as the saturation state declines. Computer models indicate that the rise in CO₂ levels expected during the coming decades will reduce calcium carbonate saturation in tropical surface waters by 30% relative to preindustrial levels. The findings are based on ocean carbon data; the coral reefs themselves have not been studied in situ.

Item #d99may2

“Solar Cycle Variability, Ozone, and Climate,” D. Shindell et al., Science, 284 (5412), 305-308 (1999).

A link between winds and temperature on the one hand and the sun and its cycles on the other has long been suspected, but the mechanism connecting the two was unknown. Previous studies neglected to take into account the effects of solar activity on the ozone layer or the complex chemistry of the upper atmosphere. When the upper atmosphere’s chemistry was added to a climate model, the results showed that, during a solar maximum, major climate changes occur in North America because of stronger westerly winds. Indeed, wind speeds and directions change all over the Earth. During the sun’s 11-year cycle, the energy released by the sun changes by only 0.1%. But when the solar cycle is at a maximum, it puts out a larger percentage of high-energy radiation, which increases the amount of ozone in the upper atmosphere. The increased ozone warms the upper atmosphere, and the warm air affects winds all the way from the stratosphere to the Earth’s surface. These results also confirm that changing levels of energy from the sun are not a major cause of global warming because the solar increases are not large enough to cause large global temperature increases.

Item #d99may3

“Large-Scale Impoverishment of Amazonian Forests by Logging and Fire,” D. C. Nepstad et al., Nature 398, 505-508 (1999).

Field surveys of wood mills and forest burning were conducted in Brazilian Amazonia. The results indicate that present estimates of annual deforestation for Brazilian Amazonia capture less than half of the forest area that is degraded or deforested each year by logging and burning. Logging alone was found to severely damage 10,000 to 15,000 km2 per year of forest that are not documented in the official government deforestation mapping programs that are used to measure Brazil’s progress in curbing forest degradation and to gauge human contributions to the atmospheric CO₂ concentration. Logging increases forest vulnerability to future burning, and both logging and fire release forest- sequestered carbon to the atmosphere. In years of severe drought, such as that brought on by El Niño, the burning is even more severe, and the percentage of damaged lands that are reported is even less.