International Herald Tribune: Moving gently through pristine blue waters, floating past whales and glaciers, fjords and islands, it is easy to see why travelers might think a vacation on a cruise ship is more eco-friendly than jetting through the earth’s atmosphere on a plane. Not so, according to Climate Care, a British-based carbon-offsetting company, whose statistics show that cruise ships emit nearly twice as much carbon dioxide as airplanes. “We now know they are far more polluting per passenger-kilometer …