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Environmental News Network (ENN)
December 9, 1997

A complex of globally interconnected ocean currents, collectively known as the Conveyor, governs our climate by transporting heat and moisture around the planet. But the Conveyor is delicately balanced and vulnerable, and it has shut down or changed direction many times in Earth's history, Professor Broecker reports. Each time the Conveyor has shifted gears, it has caused significant global temperature changes within decades, as well as large-scale wind shifts, dramatic fluctuations in atmospheric dust levels, glacial advances or retreats and other drastic changes over many regions of the Earth, he said.

The Conveyor "is the Achilles heel of the climate system," Professor Broecker wrote in Science. "The record ... indicates that this current has not run steadily, but jumped from one mode of operation to another. The changes in climate associated with these jumps have now been shown to be large, abrupt and global." Professor Broecker also offered a new theory: Scientists generally agree that periodic changes in Earth's orbit and the amount of solar radiation it receives have paced fundamental climate changes on the planet over millions of years. But the global climatic flip-flops may have been set in motion by sudden switches in the operation of the Conveyor, he said.

In recent years, evidence has mounted that the Earth frequently has experienced rapid, large-scale climate changes. Greenland ice cores have shown that during the last ice age Earth's climate switched back and forth every few thousand years between periods of intense and moderate cold, with the transitions occurring on a timescale of a few decades to as little as a few years. Each interval of intense cold was matched by the launching of great armadas of icebergs in the North Atlantic, seen in ocean sediment cores, and a great influx of dust into Earth's atmosphere, indicating a pronounced change in wind and storm patterns. Wetlands in tropical areas and mountain glaciers in Chile and New Zealand expanded and shrank in synchrony with the North Atlantic changes.