The devil is, as always, in the detail. Here, the 'air pollution' is oxides of sulphur, which are a consequence of the use of nearly regulation free dirty bunke

The devil is, as always, in the detail. Here, the 'air pollution' is oxides of sulphur, which are a consequence of the use of nearly regulation free dirty bunker fuel by ships. If the measurement is CO2, or other pollutants, it's almost certainly less bad comparatively (though in no way clean).