New York Times: Greenland Ice Sheet, 77 degrees 45 minutes N. latitude, 51 degrees 6 minutes W. longitude Jorgen Peder Steffensen made me an offer I couldn’t refuse: “If you come to Copenhagen, I will show you a Christmas snow – a real Christmas snow, the snow that fell between 1 B.C. and 1 A.D.” Now that’s an offer you don’t get every day! But then I don’t go to the Arctic Circle every day. “I can also show you a sample of the very last snow that fell right at the end of the last ice …