They're not, it's just a reminder that vast amounts of the world's pollution is also being caused by large sea vessels, of which cruise ships are a variety. It

They're not, it's just a reminder that vast amounts of the world's pollution is also being caused by large sea vessels, of which cruise ships are a variety. It's an oft neglected point in the global climate discussions because it's hard to associate their scale with a direct human impact like with cars. Tying it to a cruise ship around a populous city helps people bridge that mental gap.