Friday, 16 January 2009

Super speedy climate change in our not too distant past

I am currently reading Survival of the Sickest a riveting book on diseases and human evolution. I thought I would share a section that grabbed my attention:

"In the early 1970s, climatologists discovered that some of the best records of historic weather patterns were filed away in the glaciers and ice plateaus of northern Greenland. It was hard, treacherous work - if you're imagining the stereotypical lab rat in a white coat, think again. This was Extreme Sports: Ph.D. - multinational teams trekking across miles of ice, climbing thousands of feet, hauling tons of machines, and enduring altitude sickness and freakish cold, all so they could bore into a two-mile core of ice. But the prize was a pristine and unambiguous record of yearly precipitation and past temperature, unspoiled by milennia and willing to reveal its secrets with just a little chemical analysis. Once you paid it a visit, of course.

By the 1980s, these ice cores definitively confirmed the existence of the Younger Dryas - a severe drop in temperature that began around 13,000 years ago and lasted more than a thousand years. But that was just, well, the tip of the iceberg.

In 1989 the United States mounted an expedition to drill a core all the way to the bottom of the two-mile Greenland ice sheet - representing 110,000 years of climate history. Just twenty miles away, a European team was conducting a similar study. Four years later, both teams got to the bottom - and the meaning of rapid was about to change again.

The ice cores revealed that the Younger Dryas - the last ice age - ended in just three years. Ice age to no ice age - not in three thousand years, not in three hundred years, but in three plain years. What's more, the ice cores revealed that the onset of the Younger Dryas took just a decade. The proof was crystal clear this time - rapid climate change was very real. It was so rapid that scientists stopped using the word rapid to describe it, and started using words like abrupt and violent. Dr. Weart summed it up in his 2003 book:

Swings of temperature that scientists in the 1950s believed to take tens of thousand of years, in the 1970s to take thousands of years, and in the 1980s to take hundreds of years, were now found to take only decades.

In fact, there have been around a score of these abrupt climate changes over the last 110,000 years; the only truly stable period has been the last 11,000 years or so. Turns out, the present isn't the key to the past - it's the exception.

The most likely suspect for the onset of the Younger Dryas and the sudden return to ice age temperatures across Europe is the breakdown of the ocean "conveyor belt," or thermohaline circulation, in the Atlantic Ocean. When it's working normally - or at least the way we're used to it - the conveyor carries warm tropical water on the ocean surface to the north, where it cools, becomes denser, sinks, and is carried south through the ocean depths back to the Tropics. Under those circumstances, Britain is temperate even though it's on the same latitude as much of Siberia. But when the conveyor is disrupted - say, by a huge influx of warm fresh water melting off the Greenland ice sheet - it may have a significant impact on global climate and turn Europe into a very, very cold place."

Food for thought what with all the glacier melt underway *sheesh* Plenty of other fascinating information in this book. I highly recommend it!

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