Scientific News  Natural Cataclysm Global warming GLOBAL WARMING COULD TRIGGER CASCADE OF CLIMATIC CHANGES
GLOBAL WARMING COULD TRIGGER
CASCADE OF CLIMATIC CHANGES
Global warming and the partial melting of polar
ice sheets can dramatically affect not only sea levels but also Earth's climate,
in ways that may be complex, rapid and difficult to adjust to, scientists say in
a new study to be published Friday in the journal Science.
Sea level and climatic changes in Earth's distant
past, near the end of the last Ice Age about 14,600 years ago, offer significant
clues to some phenomena that Earth may experience in the near future, possibly
in coming decades or centuries, the study found.
The research was done by scientists at the
University of Victoria, Oregon State University, and the University of Toronto.
It revealed changes in global temperature, sea level and ocean currents that can
occur with surprising rapidity.
"With the advent of global warming, we're
trying to identify the climatic surprises that may be in store for us, the
events that we really aren't expecting," said Peter Clark, a professor of
geosciences at OSU and a co-author of the study. "The more we look at this,
the more it appears there have been large and abrupt changes in climate and sea
level that are interconnected. If these changes were to happen in the future,
they could cause huge societal disruptions."
About a year ago, Clark and his colleagues
outlined in a publication in Nature how one of the unanticipated outcomes of
global warming could be disruption of a "thermohaline circulation"
pattern in currents of the North Atlantic Ocean, robbing Europe of the influence
of warm ocean currents and causing widespread cooling. This could happen when
additional rainfall or melting glaciers in the Northern Hemisphere inject more
fresh water into the North Atlantic and make the ocean less salty.
Scientists now believe this current may have
slowed or stopped altogether many times in Earth's past. The shutdown of this
current was one prominent feature of the last Ice Age.
In the new study, the researchers found that an
Antarctic melting event called "Meltwater Pulse 1A," which occurred
near the end of the last Ice Age about 14,600 years ago, raised Earth's sea
levels about 70 feet in less than 500 years. The melting event simultaneously
caused the North Atlantic circulation to turn on, causing widespread warming of
the Northern Hemisphere.
The melting event occurred following a time of
increasing temperature, sea level and carbon dioxide that had some similarities
- and key differences - to the present day, Clark said.
"These past events provide important clues
as to how the climate system may change as the Earth warms," Clark said.
"Global warming might cause a shutdown of
currents in the North Atlantic and cause Europe to cool," he said. "But
just as people are trying to adjust to that event, the same warming might also
help melt an Antarctic ice sheet which would tend to start the current in the
North Atlantic moving again. And that might be considered a good thing, unless
you live in a coastal area which is now going to be flooded by rising sea levels."
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Publishing date: March 25, 2003
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