Every time a large volcano erupts it puts millions of tonnes of sulfur dioxide into the sky and drastically cools that hemisphere for a few years. Why would anyone think cutting millions of tonnes of ship sulfur dioxide emissions wouldn’t have the same effect. This is exactly why there is active research into adding sulfur back into aviation fuels along with nanocarbon particles to reflect sunlight from the upper atmosphere the cooling effect with millions of flights per year would be dramatic. Sulfur also has a nasty habit of forming sulfuric acid and that eats ozone....This is why the aviation fuels had sulfur removed in the first place we kinda need the ozone layer for you know plant life.