Skating over the North Pole just got a little more dangerous. Scientists have found that the sheet of ice covering earth's northernmost area has become forty percent thinner over the past four decades -- possibly the result of global warming. But don't head for the mountains just yet. Since the melting came from ice already in the ocean, global water levels will remain roughly the same. While the melting has been linked to changing wind patterns around the Arctic, researchers aren't sure whether this is a direct result of global warming. Still, the news does reflect several possibly scary trends. "We know that the amount of greenhouse gasses in the atmosphere have increased dramatically and we know that temperatures are rising," says TIME environmental editor Charles Alexander. "With the thinning of the ice layer, there are so many signs of global warming that it only makes sense to take some action." One step for Congress: ratifying the emissions-control standards of the 1997 Kyoto Treaty. The measure has been stalled there ever since President Clinton signed it two years ago; the news from up north could be one more bit of ammo for proponents. And with scientists expecting the temperature to grow another 3.5 degrees over the next century, Congressional opponents could find their arguments on thin ice.