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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 4, APRIL 1999

JOURNAL ARTICLES...
GENERAL INTEREST

Item #d99apr1

“Nitrogen Deposition Makes a Minor Contribution to Carbon Sequestration in Temperate Forests,” K. J. Nadelhoffer et al.,Nature 398, 145-148 (1999).

Fertilizer tagged with 15N was provided to temperate forests at nine sites in Europe and North America, and it was then traced through various forest compartments. Only 20% was retained by plant tissues, and only 5% was taken up by woody plants with high carbon-to-nitrogen ratios. From these values, natural nitrogen fertilization was estimated to be able to produce an uptake of only 0.25 × 1015 g C/y. This value is a very small percentage of the missing carbon in the global carbon budget and shows that nitrogen could not be producing an unrecognized carbon uptake by temperate forests.

Item #d99apr2

“Rapid Thinning of Parts of the Southern Greenland Ice Sheet,” W. Krabill et al.,Science 283 (5407), 1522- 1524 (1999).

Measurements of the thickness of the ice sheet over southern Greenland with aircraft-borne laser-altimeters in 1998 were compared to earlier measurement. They show that both thickening and thinning of the ice sheet are occurring. Ice is accumulating at rates up to 25 cm/y at higher elevations but thinning at rates up to 20 cm/y at lower elevations that are closer to the coast. Thinning rates were greatest at the lower reaches of outlet glaciers, exceeding the thinning that could be produced by decreased snowfall or increased surface melting. The researchers concluded, therefore, that the thinning was caused by accelerated creep produced by a lowering of the grounding friction by increased meltwater.

Item #d99apr3

“Biotic Feedbacks in the Warming of the Earth,” G. M. Woodwell et al.,Climatic Change 40, 495-518 (1998).

Over the past 220,000 years, warming trends have been associated with higher greenhouse-gas concentrations, and cooling periods have been associated with decreased greenhouse gases. Vegetation both absorbs CO₂ (through photosynthesis) and respirates it (through decay); respiration is the more sensitive to temperature. During the past century, vegetation has been accumulating carbon, possibly because of increased nitrogen mobilization, CO₂ fertilization, and/or Earth’s warming itself. Recently, the enhanced greenhouse effect has been the dominant influence on global temperature, and the Earth may be entering a new climate phase, as evidenced by the negative correlation between temperature and carbon uptake and the positive correlation between temperature and greenhouse-gas atmospheric concentrations. The positive feedback of vegetative decay, putting CO₂, CH₄, and N₂O into the atmosphere, could affect the warming rate significantly.

Item #d99apr4

“Regulation of Keystone Predation by Small Changes in Ocean Temperature,” E. Sanford,Science 283 (5410), 2095-2097 (1999).

The effects of water temperature on predator-prey relationships in an Oregon rocky intertidal community were studied with field and laboratory experiments with a keystone predator, the sea star Pisaster ochraceus. The combined field and laboratory results indicated that a slight lowering of water temperature by El Niño-related cold-water upwelling and changes in the timing and intensity of seasonal events decreased the sea star’s consumption of its principal prey, the mussels Mytilus californianus and Mytilus trossulus. Without predation, the diverse assemblage of intertidal algae and invertebrates changed to a monoculture of the highly competitive M. californianus.

Item #d99apr5

“A Message from Warmer Times,” M. P. Golombek,Science 283 (5407), 1470-1471 (1999).

Data from the Mars Pathfinder and Global Surveyor missions with earlier data from two Viking landings suggest a major climatic change on Mars with an early warmer and wetter environment. Erosional features are abundant. Rounded pebbles and cobbles suggest an early fluvial environment. Airborne dust particles collected by Pathfinder and the abundance of sand also support this view. Sand typically forms by way of water-dominated erosion and deposition processes. Martian climate change is expected to provide clues about Earth’s changes.