Other emissions from ships
JeffyPooh is right that bunker fuel is the something like to scrag end of the products of crude ("otherwise a waste product"). But he doesn't know much about ships or shipping. Few old ships are efficient enough to still be used - fuel is a large part of the cost - and any "old smoldering slag heaps" would soon be arrested under port state controls, they wouldn't pass flag or class inspections either.
But he continues to be right about bunkers when he states that the other emissions "ALSO HAVE A SIGNIFICANT GREENHOUSE GAS EFFECT". What he doesn't say is that the SOX emissions actually have a refridgerant effect. A major EU-funded study (CE Delft: Climate Policies for Maritime Transport. Design and assessment of possible EU policies. January 2007) has shown that shipping actually has an overall global cooling effect. Currently other emissions more than balance the global warming effects of the world fleet’s CO2 emissions.
But SOX and NOX (the problem emissions from burning bunkers) can be damaging to health if released near to land. However, regulations to reduce these pollutants in the established risk areas of the Baltic and North Sea came into force in August this year. This is why the global industry has consistently called, through the International Chamber of Shipping, for a holistic approach to the reduction of ships’ air emissions, which should seek to balance the competing pressures in the interest of finding the greenest practical solution across the piece.
SOX and NOX are far from easy to reduce (the car rating is low as the fuel has not got the NOX in it - but to use distallate fuel in ships would mean using the same amount of oil as that consumed by the EEC again (you would have to refine that much more, you can't just change the bunker fuel). That would not be good for the environment - the increased refining would mean a 15% increase in CO2 from refineries - or the shrinking oil reserves.