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.
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