https://www.theguardian.com/environment/2009/apr/09/shipping-pollution
https://www.treehugger.com/cars/just-15-of-the-worlds-biggest-ships-may-now-emit-as-much-pollution-as-all-the-worlds-760m-cars.html
https://www.theguardian.com/environment/2016/may/21/the-worlds-largest-cruise-ship-and-its-supersized-pollution-problem#img-1