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Stalagmites Provide Clues in Changing Rainfall Patterns

June 2, 2009 at 6:45 PM EST
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JIM LEHRER: And finally tonight, searching for clues about changes in weather patterns. Tom Clarke of Independent Television News reports from a remote region in southwest Poland.

TOM CLARKE: Deep in a cave, squeezing between rocks and freezing mud isn’t exactly where you’d expect to find climate scientists, but you can’t attempt to travel back in time to recreate the history of Europe’s weather without going to extremes. And trying to film their research is no simple task, either.

It’s definitely quite the squeeze, isn’t it?

Husband and wife team Lisa and James Baldini are paleoclimatologists at Durham University. They’re using cave stalagmites to unravel the history of a climate pattern called the North Atlantic Oscillation.

As the name suggests, it’s a weather phenomenon that swings back and forward, like the Pacific’s El Nino, only for Europe.

DR. LISA BALDINI, paleoclimatologist, Durham University: It’s got a major impact on European climate. And it’s important to know how this has changed in the past.

TOM CLARKE: The NAO’s past can inform today’s forecasters, who know how crucial the weather pattern is.

DR. ADAM SCAIFE, Met Office, Hadley Center: It’s the most important single factor, actually, that determines the year-to-year changes in the weather. When the NAO is positive, in its strong phase, then we have strong westerly winds across the Atlantic. These bring mild wet air off the Atlantic into the U.K. That creates more rainfall, and so we get more flooding during those winters.

During winters when the NAO is negative, then the winds are much weaker and often the air actually comes from the east. And that can bring cold Siberian air into the U.K. and Northern Europe, and that gives us cold, dry conditions.

Far-reaching effects

TOM CLARKE: The extreme summer flooding of two years ago and this winter's severe cold snap were linked to the NAO, but its effects can be far reaching, too. It's been linked to cod stocks in the Atlantic, hurricane intensity in the United States, and English wheat harvests.

Its history is locked up in rainfall records. Written ones go back a few hundred years. Tree rings can hint at rainfall going back a millennium or so. But the Durham team have now discovered the stalagmites from this cave near Poland's Tatra Mountains take rainfall records back 20,000 years.

Even though it never rains in caves, weird and wonderful stalagmites growing up from the cave floor can faithfully record rainfall.

Rainwater has been seeping through the roof of this cave, laying down these stalagmites over tens of thousands of years. And each drip has carried with it a tiny bit of information about what's going on with the ever-changing climate outside.

But to tell the weather from a stalagmite, you need to know how fast it grows. Last year, the team took three stalagmites from the cave and replaced them with high-tech equipment to count drips hitting the same point. Now they're back to recall the data and accurately date their stalagmites.

They're using some of the latest technology, a computer-controlled micro-mill to extract the chemical signatures locked up in individual layers of stalagmite. By analyzing them, they can tell whether it was raining, how hard, and even how warm it was at the time.

DR. JAMES BALDINI, paleoclimatologist, Durham University: Hurricanes can be picked up. Individual storms can be picked up from stalagmites. It's all about finding the right sample and using the right analytical technique to extract the perfect signal from the sample.

TOM CLARKE: But to be of use to climate forecasters, they'll need to show evidence of the NAO fluctuating over the past several thousand years, influencing the rain record in their stalagmites. If they succeed, this history of the NAO could be invaluable for improving computer models we're increasingly reliant on.

DR. ADAM SCAIFE: It will help us to understand how the NAO works. And only by understanding how the NAO works will we be able to produce models that can accurately represent that physics. And those models will be the best at predicting the future.

TOM CLARKE: If they can link the North Atlantic Oscillation to stalagmites in Poland, the Baldinis are planning to find caves elsewhere in the world that could tell us how climate change will affect other powerful weather systems like El Nino or the Indian monsoon.