For decades, shipping sulfur emissions were acting as an accidental planetary air conditioner. When ships burned high-sulfur fuel oil containing up to 3.5% sulfur, they were pumping massive amounts of sulfur dioxide into the atmosphere – about 10-13 teragrams per year globally, representing 14% of all sulfur dioxide emissions. This wasn't just pollution; it was an unintentional geoengineering project that had been cooling the planet for over a century.​

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