Ancient Climate May Augur Future Effects Of Global
Warming
by Matthew Huber
West Lafayette - Feb 12, 2003
Ancient lake sediments and modern computers both
indicate that El Nino might react differently to
global warming than current theory claims, according
to a Purdue research report.
Purdue University's Matt Huber has simulated the
"hothouse" climate of the distant past with a computer
model to study the reaction of the tropical Pacific
Ocean, a key player in removing heat from the
atmosphere.
While it cannot absorb an unlimited amount of
atmospheric heat, Huber has found that even when the
climate warms, the tropical Pacific Ocean maintains
its ability to remove heat periodically - the
permanent loss of which could encourage runaway global
warming.
Huber has found historical evidence for his theory in
45 million-year-old lake sediments, which may indicate
that the relationship between global warming and El
Nino needs to be re-examined.
"The tropical Pacific's ability to cool the atmosphere
may be less susceptible to global warming's effects
than we believed," said Huber, an assistant professor
of earth and atmospheric sciences in Purdue's School
of Science. "We should still be greatly concerned
about global warming, but it appears that one
mechanism involved in climate change operates
differently than we have imagined."
The research appears in the Feb. 7 issue of Science.
In the decades since theories of global warming came
to prominence, there has been intense scientific
debate over how an influx of greenhouse gases into the
atmosphere would affect the Earth's climate,
particularly El Nino-La Nina oscillations.
El Nino refers to a warming of the surface layers of
the eastern Pacific Ocean, which occurs in those years
when the prevailing westerly winds in the South
Pacific die down, allowing the warm waters from the
western Pacific to slosh eastward. Conversely, in a La
Nina year, the winds pile up warm water in the western
Pacific and drag cooler water up from the depths in
the east.
For the past several millennia the Pacific has
alternated between these two states in an irregular
but basically stable oscillation.
"A question climate scientists have debated is whether
future global warming might make the oscillation
stop," Huber said. "The worry is that Earth would
suffer a runaway greenhouse effect if that happened."
Ordinarily the cool surface layer of the eastern
Pacific absorbs heat from the tropical atmosphere and
carries it far away via ocean currents that flow
hundreds of meters below the surface. But in an El
Nino year, both the shallows and depths grow so warm
that the atmospheric heat has nowhere to go, causing a
warming of the tropics and strange weather patterns
worldwide.
"If you compare the eastern Pacific to a water-cooled
radiator, then the ocean currents are the coolant that
absorbs atmospheric heat," Huber said.
"El Nino heats the radiator to the point where it
can't do its job. Nowadays, El Nino events are too
brief to have lasting effect, but some have theorized
that if the oscillation stops the Earth will suffer a
'continuous El Nino-like state' that would warm the
planet very quickly."
Huber's desire to ground such theories with historical
evidence led him to examine a period of the distant
past when the Earth's climate was considerably warmer
- the Eocene epoch. During the Eocene, nearly 50
million years ago, palm trees grew in the north of
England and alligators thrived far above the Arctic
Circle on Canada's Ellesmere Island.
"We figured that if a continuous El Nino state had
ever existed, it would have been during the Eocene,"
Huber said. "So we decided to use a computer model of
the Eocene's climate to see what the eastern Pacific
Ocean would do."
Huber and Rodrigo Caballero, both working at the time
at Denmark's Neils Bohr Institute, spent several years
simulating the Eocene atmosphere and oceans with
computers at the National Center for Atmospheric
Research in Boulder, Colorado. Their results, which
surprised even them, indicated that the tropical
oceans were more resilient at absorbing heat than
current theory states.
"It seems that when the global climate was
considerably warmer, the tropical eastern Pacific was
still relatively cool, even though most theories
suggest it would have warmed as well," Huber said.
"It turns out these theories were not wrong, merely
oversimplified. Instead of a two-layer ocean, with
shallows that absorb heat and depths that carry it
away, there was a third layer wedged between them. It
was this third layer that was the key to it all."
Huber theorizes this third layer of water remained
cool even when the temperature increased above and
below it. This wedge, which in Huber's computer model
extends across thousands of miles of ocean, would
enable the radiator to keep operating despite a high
level of atmospheric greenhouse gases.
"The wedge formed a cool barrier between the warmer
shallows and depths," Huber said. "It was a place for
the heat to go from above, and, for complex reasons,
it did not absorb heat from the depths. The computer
model told us that for this reason the Eocene tropics
were not much different than they are today, even
though the Earth's poles were much warmer."
All these results could be written off as merely so
much computer gaming, but Huber found that other
scientists had turned up evidence for ancient El Nino
events in the sediments of ancient lakebeds in
present-day Wyoming and Germany.
"These lakes were far from the Pacific Ocean, but they
still felt the effects of El Nino," Huber said.
"Sediment records show that El Nino events occurred in
the Eocene with the exact same frequency as the
computer model shows. In short, there was no
continuous El Nino state, even though the Earth's
climate was considerably warmer."
While such news might imply that we can be less
concerned about global warming, Huber is careful to
point out that his research does not contradict the
climatic catastrophes that global warming will
supposedly bring.
"Just because the tropics appear to be more resilient
than we had thought does not mean that they will
remain comfortable regions even if the globe warms up
significantly," he said.
"Global warming could make their average temperatures
rise at least 10 degrees Celsius. It may also bring
the more extreme storms and disastrous rises in ocean
water levels that scientists have predicted for
decades. It's important to remember that we are
clarifying a single important aspect of the global
heat engine, but not reimagining the net result of
global warming on our climate as a whole."
Huber said he would like the research to inspire
further investigation of climate history, which will
be necessary to bolster his theory.
"The major weakness of this study is that we have
taken data from lakebeds in Wyoming and Germany, but
not from the tropics themselves," he said. "While
these ancient lakes were affected by El Nino in their
day, it would be useful to have tropical records of El
Nino from 50 million years ago as well."
Funding for this research was provided in part by a
grant from the National Science Foundation and
involved support from, and collaboration with, Lisa
Sloan of the University of California Santa Cruz,
Bette Otto-Bliesner at the National Center for
Atmospheric Research and the Danish Center for Earth
System Science.
=====
-----------------------------------------------------------------------
John D. Giorgis - [EMAIL PROTECTED]
Tonight I have a message for the brave and oppressed people of Iraq:
Your enemy is not surrounding your country � your enemy is ruling your
country. And the day he and his regime are removed from power will be
the day of your liberation." -George W. Bush 1/29/03
__________________________________________________
Do you Yahoo!?
Yahoo! Shopping - Send Flowers for Valentine's Day
http://shopping.yahoo.com
_______________________________________________
http://www.mccmedia.com/mailman/listinfo/brin-l
