Comets, Climate Change, and Extinctions—1

by Emil Morhardt

At the end of the last ice age as the Earth was warming to its present condition there was an unexplained 1000-year pause and partial reversal in the warming (called the Younger-Dryas stadial). The result was a millennium of very cold weather in the Northern Hemisphere. The cause was widely attributed to the abrupt stoppage of the Gulf Stream; warm water was no longer transported from the equator north past the US east coast and Europe toward Greenland. The physical cause of the stoppage was presumably the melting of the Laurentide Ice Sheet covering Canada; enough freshwater flowed out over the North Atlantic near Greenland, that it formed a thick layer on top of the ocean that was not dense enough to sink through the underlying salt water. It is sinking saltwater off Greenland that drives the major global ocean currents—the Meridional Overturning Circulation (MOC)—of which the Gulf Stream is the last leg. Scientists are somewhat worried that under the current warming conditions, enough meltwater could flow off the Greenland Ice sheet to wreak the same sort of havoc…a much colder North America and Europe in the midst of a generally warming globe. In 2007, Firestone et al. presented an unexpected theory that the trigger for the freshwater outflow 12,900 years ago was an extraterrestrial (ET) impact event—a comet or meteorite—that also directly led to the Continue reading