he sea ice at the North Pole is only a few feet thick. It floats on an ocean that is 14,000 feet deep. And it's cracking under our feet. A global warming expert suggests what to do... Everything you hear -- all the chugging and huffing and banging -- is the ice beneath us. Read about it in my new book THE NORTH POLE WAS HERE. First Chapter free online at www.nytimes.com/learning/globalwarming I'm Andrew Revkin. I cover global warming and other environemtnal issues for The New York Times. Search for my stories on Al Gore's new movie, "An Inconvient Truth," on President Bush's climate policies, and more. My other multimedia work on the Arctic is here: www.nytimes.com/pages/science/sciencerep ort global warming global warming