Research has shown that the 15 biggest ships produce more sulphur oxide pollutants than ALL the 960 million cars in the world. Too many independent surveys carried out to include here but see asexample http://www.airclim.org/air-pollution-ships
. Whereas land based emissions are being decreased year on year the shipping trend is going in the opposite direction. With a constant flow of cruise ships at Southampton, on occasions 5 a day, and average of 3 container ships this independent report highlights the problem http://www.independent.co.uk/news/world/pollution-cruise-ships-po-oceana-higher-piccadilly-circus-channel-4-dispatches-a7821911.html
. Pollution on deck of cruise ship is higher than that of Shanghai or Delhi. Per day one cruise ship emits as much particulate matter as a million cars. So 30 cruise ships pollute as much as all the cars in the United Kingdom.