The largest cruise ship to ever sail the Northwest Passage is en route to New York City from Alaska. The Crystal Serenity left Seward, Alaska, in mid-August and plans to dock in New York on Sept. 16. The ship sailed up the Bering Strait, and made a port call in Nome where guests got a chance to see a herd of wild musk oxen that had taken up residence just outside town. The ship then continued north until reaching the Arctic Ocean, and then east toward Greenland. The melting Arctic is making this type of trip possible. The irony isn't lost on Michael Byers, a professor in the political science department at the University of British Columbia in Vancouver. He calls it ''extinction tourism.'' The 900 or so passengers on the luxury liner are going through the Arctic to seen an ecosystem before it disappears. But Byers say they are actually adding to the problem because of the ship's large carbon footprint.