Further evidence found of global warming
Thursday, April 23, 1998
Three years in the decade of the 90s
have been found to be warmest on
record of all years dating back to
1400 A.D. This finding bolsters the
argument that the Earth is warming
at least in part due to human
emissions of so-called greenhouse
gasses, according to a study
published in current issue of the
journal Nature.
Climatologists at the University of
Massachusetts and Amherst,
working on a National Science
Foundation-funded study, have
reconstructed global temperature over the past 600 years and determined that 1997,
1995 and 1990 were the warmest.
"This study adds solid information to the growing base of data which points to the
warming of our planet by human-related activities," says Herman Zimmerman, program
director in NSF's division of atmospheric sciences. "The balance of evidence now
firmly supports an important human influence on the global climate system. This is a
serious problem for people everywhere, and it needs to be addressed at all levels of
government."
The researchers, who were able to estimate temperatures over more than half the
surface of the globe, pinpointing northern hemisphere yearly temperatures to a fraction
of a degree back to 1400 A.D., focused on factors that have a significant influence on
the climate but are not a part of the climate system itself.
Based on statistical comparisons of reconstructed northern hemisphere temperatures,
the best estimates indicate that natural changes in the brightness of the sun and volcanic
emissions both played an important role in governing climate variations over the period
studied.
However, over the past few decades, greenhouse gases produced by human activities
appear to have had an increasing influence on temperatures. "The anomalous warmth of
several recent years appears likely to be related to human influences on climate," said
researcher Michael Mann from U. Mass.
The study bears out concerns voiced by scientists in recent years regarding global
warming, researcher Raymond Bradley, also of U. Mass, said.
Scientists have shown that over the last century carbon dioxide levels in the atmosphere
have increased by 25 percent as a direct result of industrialization.
Scientists predict that if the amount of carbon dioxide in the atmosphere were to
continue to increase at its current rate, it could rise to double its pre-industrial level
during the next century, leading to a magnification of the already observed warming.
For example, melting ice caps could raise sea levels, threatening coastal regions with
more frequent flooding. The planet as a whole might expect to see frequent extreme
weather events, Mann said. "Heat waves and droughts could become more common,
and more intense."
However, the climatologists expressed concern about the degrees of uncertainty
surrounding increased or accelerated global warming.
"We have a sense of what might happen to the planet as a whole, but the fact is, we
don't really know what the regional impacts might be," said Mann.
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