Friday, April 2, 2010

Climate History Conundrums

One of the most puzzling climate changes of the past 100,000 years occurred at the end of the last Ice Age. By 13,500 years ago the world was rapidly warming and the glaciers were retreating. Around 13,000 years ago, quite suddenly, the world returned to glacial conditions for 500 years, a period we call the Younger Dryas. The change was quite dramatic:
At its onset, temperatures in northern Europe suddenly dropped 10 °C or more in decades, and tundra replaced the forest that had been regaining its hold on the land.
The most widely accepted explanation for this sudden change has been that a vast lake of fresh water formed by the melting glaciers suddenly poured into the Atlantic Ocean, disrupting ocean currents and thus the global climate. Now geologists have presented evidence, via an article in Nature, that the glacial lakes actually emptied northward, into the Arctic Ocean. This would invalidate 20 years worth of modeling based on all thatfresh water flowing into the Atlantic -- I have personally met two graduate students who were writing dissertations about how the emptying of the glacial lakes into the Atlantic would change the climate-- and throw the question of what caused the Younger Dryas wide open.

And this brings me to the question of scientific hubris. Both of those graduate students I met seemed completely convinced that there was a great flow of glacial meltwater into the Atlantic, and that this changed the climate. But, see, there was never any actual geological evidence that all that water went down the St. Lawrence River as their models required. It was jut a guess. If these latest findings hold up, it will turn out to have been the wrong guess, and all of their calculations will be castles in the air.

The question of what all that CO2 we are pumping into the air will do to the climate has created huge pressure on climate scientists to find answers, solid answers on which policy can be based. I don't believe we have such solid answers. Alas, "we don't know what will happen but it might be very bad" doesn't seem to be a powerful argument in contemporary politics. To get political action we need scientific-looking graphs that show certain doom. The whole atmosphere of political urgency pushes the scientists even further toward exaggerating the certainty of their own results, which is one of the besetting sins of science anyway.

Even a little history would teach scientists how easy it is to be wrong. We should be more humble about the mystery of the world and less confident of our own intellectual prowess.

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