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GSA Today, v. 9, no. 1, January 1999
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Table of Contents
Science Article: (View Abstract)
What If the Conveyor were to Shut Down? Reflections on a Possible Outcome of
the Great Global Experiment
by W. S. Broecker
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What If the Conveyor were to Shut Down?
Reflections on a Possible Outcome of the Great Global Experiment
by W. S. Broecker
ABSTRACT
Suggestions that the ongoing greenhouse buildup might induce a shutdown of the
ocean's thermohaline circulation raise the questions as to how Earth's climate
would change if such an event were to occur. The answer preferred by the popular
press is that conditions akin to those that characterized the Younger Dryas-the
last kiloyear cold snap-would return. But this extreme scenario is an unlikely
one, for models suggest that in order to force a conveyor shutdown, Earth would
have to undergo a 4 to 5 °C greenhouse warming. Hence, the conditions
at the onset of the shutdown would be very different from those that preceded
the Younger Dryas. Thus, it is unlikely that new climate conditions would be nearly
so severe. Unfortunately, because no atmospheric model to date has been able to
create the observed large and abrupt changes in climate state of Earth's atmosphere,
we lack even the crudest road map. However, as was the case for each of the abrupt
changes recorded in Greenland's ice, if the conveyor were to shut down, climate
would likely flicker for several decades before locking into its new state. The
consequences to agricultural production of these flickers would likely be profound.
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