Mother Nature Network: By the time today's babies graduate college, there's a very good chance they could celebrate with a cruise across the North Pole. That's according to the latest study on Arctic summer sea ice, the frozen pack that lingers through the Northern Hemisphere summer. In past decades, there's been less summer ice, and it's growing thinner. The research, published online Feb. 21 in the journal Geophysical Research Letters, says major sea ice loss could come within a decade or two, though some ice will...