"you have to take account of the huge loads carried by shipping. Ships carry about 90% of the world's intercontinental cargo over huge distances and their carbon pollution is only a fraction of airfreight - although their sulfur output is much higher. A recent Cambridge University comparative study shows that, per Freight-Tonne-Km (FTK), oceangoing container ships emit about 7% of CO2, about 8 times as much sulphur dioxide (CO2) and about 40% of the Nitrous Dioxide (NO2) of airfreight. So if ships converted to more expensive low-sulphur fuel, they would look much better."

Each new supertanker puts out equivalent pollution to 50 million new cars...the entire earth's annual production.

On the journey across the ocean from Japan to America, a ship full of cars puts out more pollution than all the cars will over their entire lifetime.

@HG
Sulphur is needed by every organism that grows in the seas.

This may be true but you have to consider the form the sulphur takes. "Sulfur can exist as inorganic forms, such as sulfate and hydrogen sulfide, and in organic forms in which the sulfur is still bound to partially decomposed organic matter. In certain environments, sulfur can exist is gaseous form and has the characteristic "rotten egg" smell. Once acquired, plants and animals utilize sulfur in the formation of cysteine and methionine, which are incorporated into proteins and enzymes necessary for cellular maintenance and growth.

The movement of sulfur through the food web begins with plants assimilating inorganic sulfur from the soil. Organic forms of sulfur are first broken down and decomposed by soil microbes, which then makes nutrients such as sulfur, nitrogen and phosphorus, available for plants to take them in through their roots.

For animals to obtain sulfur, they need to feed on either plants or other animals. The sulfur bound in the living tissue can be broken down and utilized by the consuming animal. Based on the dry weight of an organism, sulfur averages 1 percent of tissue mass across all living organisms.

The movement of sulfur through soil, plants, animals and the atmosphere relies heavily of the activity of soil microorganisms. Soil microbes are responsible for converting the organic forms of sulfur to the inorganic forms, which then become available for plants."

Note how none of that mentions sulphur dioxide. Compairing life's need for sulphur to sulphur dioxide pollution is like promising your girl a diamond ring and then poisoning her with carbon monoxide.