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NSF PR 97-67 - October 30, 1997
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Plant Growth Surges after Global Temperature Spikes,
Scientists Report
Study Highlights Importance of
Regional Analyses
El Nino events or volcanic eruptions can boost or
depress global temperatures within months, but their
strongest impacts on the earth's biosphere may not
occur until one to three years later, according to
a paper published in the October 31st issue of Science.
Regional analyses show that a global warm spell's
initial boost in plant activity is clustered in polar
and temperate areas. On the other hand, heat-stressed
tropical and semiarid regions may show an initial
drop in plant production.
The results, reported by scientists affiliated with
the National Science Foundation (NSF)-funded National
Center for Atmospheric Research (NCAR) in Boulder,
Colorado, lend credence to the notion that biological
effects of global change can vary substantially across
the globe.
According to NCAR's David Schimel, one of the paper's
authors, the results highlight the power of new data
sets on global change, as well as the usefulness of
computer models that connect the atmosphere and biosphere.
"We were looking specifically for delayed ecosystem
responses in this study because they had been predicted
by the models," Schimel notes.
The global temperature record revealed several multiyear
patterns, including warming associated with El Nino
events in the 1980s. These patterns were correlated
globally with carbon dioxide levels and regionally
with vegetation growth. Global carbon dioxide levels,
which are steadily rising due to human activities,
tended to rise more quickly over the first few months
after a global temperature peak. The carbon dioxide
levels rose at a slower pace during the one-to-three-year
period after the temperature peak, followed by another
gradual acceleration.
The authors studied the temperature-vegetation relationship
by region at data points separated by one degree latitude
and longitude (roughly 85 by 110 kilometers, or 50
by 70 miles). At the peak of a warm period, plant
growth tended to increase in polar and temperate regions
and decrease at lower latitudes, including tropical
rainforests and drier savanna/grassland regimes. "This
contrast suggests that . . . temperature may have
direct negative impacts on plant growth, or may increase
water stress in semiarid ecosystems," the authors
note.
However, in the one-to-three-year period after a temperature
peak, the patterns appear to reverse: plant growth
is enhanced in the warmer and drier regions and limited
at higher latitudes. Thus, low-latitude plant growth
appears to be driving the enhanced uptake of carbon
dioxide during this period.
The paper highlights the importance of regional analyses
of climate change to detect areas where effects may
run counter to a global average. This is the first
data-based study to consider regionally-specific ecosystem
responses on a global scale, says Schimel. The results
show that ecosystems are sensitive to temperature
perturbations.
Co-authors of the paper include Schimel, and Rob Braswell,
Ernst Linder and Berrien Moore, of the University
of New Hampshire (UNH).
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