A New Weather Wild Card

A new study out Thursday in the journal Science reports that there's a third weather wild card in the Atlantic. This one generates both mild and wild climates in North America and Europe.

CBS News Correspondent John Roberts reports that on one side of the Atlantic, people are wondering if winter as we know it is gone forever. On the other side, where record snow has fallen, they're wondering if it will ever end. So what in the world is going on?

Scientists say it could be a little publicized event known as the North Atlantic Oscillation (NAO).

The phenomenon is characterized by a difference in strength between a low pressure system that sits over Iceland and a high pressure system centered over the Azores.

"As that pressure changes back and forth, it changes the jet stream. The jet stream has a big influence on our weather, either causing us to have either warm, mild winters, or very severe winters," explained scientist James Baker.

For 30 years, the oscillation was high. Strong pressure systems sped up and flattened out the jet stream bringing cold Arctic air into the Northeast. But for the past two years, the system has been weaker - the jet stream more curved, and the flow more south to north.

"We can get warm humid air coming up from the Gulf of Mexico that gives us a real warm winter for example, some of the things that we're seeing right now," Baker said.

But while Boston prepares for record temperatures, across the Atlantic the effect is reversed, driving down enough cold air for record snows to trigger deadly avalanches in the French Alps.

"As to why it happens, it's a kind of complicated connection between the ocean temperatures and the atmosphere in a way that I have to admit, we don't fully understand," Baker said.

Unlike the El Nino effect, which occurs when a huge pool of warm water moves east across the Pacific, the NAO is more of a wind phenomenon. And unlike El Nino, which seems to occur every 3-7 years, the NAO is more unpredictable, sometimes measured in decades. But getting a better idea of how it works may help us to understand how the weather may change.

"The successful prediction of El Nino has really made people think that if we can predict that, we can maybe predict others as well. So It's really a big jigsaw puzzle and we're filling in the pieces," said Julia Uppenbrink of the journal Science.

Though the North Atlantic Oscillation isn't as powerful as El Nino, its effects are more far reaching. And there is some evidence the NAO may have helped trigger last year's record-setting El Nino event.
  • CBSNews.com staff CBSNews.com staff

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