Scientists have discovered that the recent spike in global temperatures may be caused by a reduction in sulfur dioxide pollution from shipping vessels. Ships have long emitted sulfur dioxide, which cools the planet by seeding clouds and reflecting sunlight. However, new regulations that limit sulfur in ship fuels took effect in 2020, leading to a loss of this cooling effect equivalent to a large volcanic eruption each year. Models show this reduction in sulfur dioxide pollution can explain the extra warming seen in the North Atlantic. While pollution is bad, the new regulations provide a natural experiment that gives insight into how intentional geoengineering could potentially combat climate change in the future.