“In 2016, the UN’s International Maritime Organization announced that by 2020, international shipping vessels will have to significantly cut sulfur pollution. Specifically, ship owners must switch to fuels with no more than 0.5 percent sulfur content, down from the current 3.5 percent, or install exhaust cleaning systems that achieve the same reduction.” That sounds like a good thing, right? But when it comes to climate change, the situation is often more complex than it first appears. It turns out that all the shipping pollution may have been helping us. James Temple explains: We’re about to kill a massive, accidental experiment in reducing global warming.