February 28, 2007
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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
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.
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.
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 Earths 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
Regulation of Keystone Predation by Small Changes in Ocean
Temperature, E. Sanford,Science 283 (5410),
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
stars 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.
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 Earths changes.
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