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Saturday, May 19, 2012
Stalagmites Map Past Tropical Climate
This is very good news. It tells us the violent swings observed at
the poles are barely reflected in the tropics at all.
Thus it is reasonable that a mere one degree forcing caused by our
passage through the Sirius cluster would warm things up considerably
but that the tropics are already about as warm as they can be. Thus
the surplus heat would simply flow to the poles which is what we have
been observing during the recent warming spell.
This would be effected mostly by warmer water flows leaving the
tropics transporting the surplus heat.
Thus these Polar anomalies are actual records of heat events that
were large enough to warm the planet itself significantly. I had
already concluded as much when I wrote my review of the Vostok ice
core and this pretty well defines the nature of the event.
The times should have experienced more weather turbulence although
even that may not have been excessive.
use stalagmites to study past climate change
by Staff Writers
Pasadena CA (SPX)
May 14, 2012
like these from northern Borneo are the ice cores of the tropics.
There is an old trick
for remembering the difference between stalactites and stalagmites in
a cave: Stalactites hold tight to the ceiling while stalagmites might
one day grow to reach the ceiling. Now, it seems, stalagmites might
also fill a hole in our understanding of Earth's climate system and
how that system is likely to respond to the rapid increase in
atmospheric carbon dioxide since preindustrial times.
existing historical climate records are biased to the high latitudes-
coming from polar ice cores and North Atlantic deep ocean sediments.
Yet a main driver of climate variability today is El Nino,
which is a completely tropical phenomenon. All of this begs the
question: How do we study such tropical climate influences? The
are the ice cores of the tropics," says Jess Adkins,
professor of geochemistry and global environmental science at the
California Institute of Technology (Caltech).
He and geochemist Kim
Cobb of the Georgia Institute of Technology led a team that collected
samples from stalagmites in caves in northern Borneo and measured
their levels of oxygen isotopes to reconstruct a history of the
tropical West Pacific's climate over four glacial cycles during the
late Pleistocene era (from 570,000 to 210,000 years ago).
The results appear in
the May 3 issue of Science Express. The lead author of the paper,
Nele Meckler, completed most of the work as a postdoctoral scholar at
Caltech and is now at the Geological Institute of ETH Zurich.
Earth's history, global climate has shifted between
periods of glacial cooling that led to ice ages, and interglacial
periods of relative warmth, such as the present.
studies from high latitudes have indicated that about 430,000 years
ago-at a point known as the Mid-Brunhes Event (MBE)-peak temperatures
and levels of atmospheric carbon dioxide in
interglacial cycles were suddenly bumped up by about a third. But no
one has known whether this was also the case closer to the equator.
By studying the
records from tropical stalagmites, Adkins and his team found no
evidence of such a bump. Instead, precipitation levels remained the
same across the glacial cycles, indicating that the tropics did
not experience a major shift in peak interglacial conditions
following the MBE.
records have glacial cycles in them, but the warm times-the
interglacials-don't change in the same way as they do at high
latitudes," Adkins says. "We don't know what that tells us
yet, but this is the first time the difference has been recorded."
the same time, some changes did appear in the climate records from
both the high latitudes and the tropics. The researchers found that
extreme drying in the tropics coincided with abrupt climate changes
in the North Atlantic, at the tail end of glacial periods. It is
thought that these rapid climate changes, known as Heinrich events,
are triggered by large ice sheets suddenly plunging into the ocean.
"In the tropics,
we see these events as very sharp periods of drying in the stalagmite
record," Adkins says. "We think that these droughts
indicate that the tropics experienced a more El Nino-like climate at
those times, causing them to dry out."
During El Nino events,
warm waters from the tropics, near Borneo, shift toward the center of
the Pacific Ocean, often delivering heavier rainfall than usual to
the western United States while leaving Indonesia and its neighbors
extremely dry and prone to forest fires.
The fact that the
tropics responded to Heinrich events, but not to the shift that
affected the high latitudes following the MBE, suggests that the
climate system has two modes of responding to significant changes.
"It makes you
wonder if maybe the climate system cares about what sort of hammer
you hit it with," Adkins says.
"If you nudge the
system consistently over long timescales, the tropics seem to be able
to continue independently of the high latitudes. But if you suddenly
whack the climate system with a big hammer, the impact spreads out
and shows up in the tropics."
This work raises
questions about the future in light of recent increases in
atmospheric carbon dioxide: Is this increase more like a constant
push? Or is it a whack with a big hammer?
case could be made for either one of these scenarios, says Adkins,
but he adds that it would be easiest to argue that the forcing is
more like a sudden whack, since the amount
of carbon dioxide in the atmosphere has
increased at such an unprecedented rate.
addition to Adkins, Cobb, and Meckler, other coauthors on the paper,
"Interglacial hydroclimate in the tropical West Pacific through
the late Pleistocene," are Matthew Clarkson of the University of
Edinburgh and Harald Sodemann of ETH Zurich. Cobb is also a former
postdoctoral scholar in Adkins's group and has been collaborating on
this project since her time at Caltech. The work was supported by the
National Science Foundation, the Swiss National Science Foundation,
the German Research Foundation, and by an Edinburgh University
Principal's Career Development PhD Scholarship.