Wednesday, June 21, 2006

Free article alert American Scientist has an article from their current issue up on the thermohaline cycle and it touches on the possible cause of the Younger Dryas:

The Source of Europe's Mild Climate
If you grow up in England, as I did, a few items of unquestioned wisdom are passed down to you from the preceding generation. Along with stories of a plucky island race with a glorious past and the benefits of drinking unbelievable quantities of milky tea, you will be told that England is blessed with its pleasant climate courtesy of the Gulf Stream, that huge current of warm water that flows northeast across the Atlantic from its source in the Gulf of Mexico. That the Gulf Stream is responsible for Europe's mild winters is widely known and accepted, but, as I will show, it is nothing more than the earth-science equivalent of an urban legend.

He mentions spending some part of his career in Seattle which does indeed have a climate quite similar to England, and noticing that this area doesn't have a Gulf Stream-like phenomenon providing it with a mild climate. He posits two main contributions: 1) The basic marine climate of land masses east of the ocean. Ocean water acts as a convenient heat sink, moderating temperature, and since weather moves east in the northern hemisphere, cold continental air is blocked. 2) Large scale waves in air masses as they compress over the Rockies and uncompress on the other side. This has the effect of causing a counterclockwise rotation of the air masses bringing cold air down from the Arctic over the continent and warm air up from the tropic over the Atlantic.

They also calculated that a complete shutting down of the thermohaline circulation would not cause as much of an effect as thought, and not nearly enough to bring about the Younger Dryas. He doesn't offer an alternative for what caused it though.