 When the vessel comes alongside, that's when she ends up turning off her vessel engines, and then she goes completely off of our local grid. That reduces the ship's emissions by more than 95% while it's in port. Cruise ships have been targeted by environmental groups. The major cruise lines signed on to a pledge to reduce their carbon footprint to net zero by 2050. Greg Allen, NPR News, Miami. And I'm Giles Snyder. This is NPR News.