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CLIMATE
CHANGE & ENVIRONMENT
Global warming is the greatest
in the past decade
Washington: A research has indicated
that global warming has been the greatest
in the past decade, with surface temperatures in the
Northern Hemisphere found
to be warmer over the last 10 years than any time
during the last 1300 years.
In fact, if the climate scientists include the somewhat
controversial data derived
from tree-ring records, the warming is anomalous for
at least 1700 years. "Some
have argued that tree-ring data is unacceptable for
this type of study," said
Michael Mann, associate professor of meteorology and
geosciences and director
of Penn State's Earth System Science Center. "Now
we can eliminate tree rings
and still have enough data from other so-called 'proxies'
to derive a long-term
Northern Hemisphere temperature record," he added.
The proxies used by the researchers included information
from marine and lake sediment cores, ice cores, coral
cores and tree rings. According to Mann, "We
looked at a much expanded database and our methods
are more sophisticated than those used previously."
"Conclusions are less definitive for the Southern
Hemisphere and globe, which we attribute to larger
uncertainties arising from the sparser available proxy
data in the Southern Hemisphere," he added. The
National Research Council suggested revisiting surface
temperatures in their "Surface Temperature Reconstructions
for the Last 2,000 Years," to include newer data
and techniques and confirmed results of a 1990s paper
by Mann and colleagues. Results of this study without
tree-ring data show that for the Northern Hemisphere,
the last 10 years are likely unusually warm for not
just the past 1,000 as reported in the 1990s paper
and others, but for at least another 300 years going
back to about A.D. 700 without using tree-ring data.
The same conclusion holds back to A.D. 300 if the
researchers include tree-ring data. "Ten years
ago, we could not simply eliminate all the tree-ring
data from our network because we did not have enough
other proxy climate records to piece together a reliable
global record," said Mann. "With the considerably
expanded networks of data now available, we can indeed
obtain a reliable long-term record without using tree
rings," he added. The new study shows that, with
caveats, tree-ring data can be used, but that even
without including that data, it is clear that the
anomalous nature of recent warmth, which most scientists
believe to be a result of human impacts on climate,
is a reality.
-Sept
2, 2008
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