Shipping is by far the biggest transport polluter in the world. There are 760 million cars in the world today emitting approx 78,599 tons of Sulphur Oxides (SOx) annually. The world's 90,000 vessels burn approx 370 million tons of fuel per year emitting 20 million tons of Sulphur Oxides. That equates to 260 times more Sulphur Oxides being emitted by ships than the worlds entire car fleet.
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Oddly enough there is never any mention of alternative power sources such as nuclear power. Nuclear marine propulsion has been in widespread naval use for over 50 years starting in 1955. There are 150 ships in operation that use nuclear propulsion with most being submarines, although they range from ice breakers to aircraft carriers. A Nimitz class supercarrier has more than twice as much power (240,000 hp, 208 MW) as the largest container ship diesel engines ever built and is capable of continuously operating for 20 years without refueling (some French Rubis-class submarines can go 30 years between refueling). The U.S. Navy has accumulated over 5,400 "reactor years" of accident-free experience, and operates more than 80 nuclear-powered ships.
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https://newatlas.com/shipping-pollution/11526/
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