In January 2022, the underwater volcano Hunga Tonga-Hunga Ha'apai in the South Pacific produced one of the most powerful eruptions in modern history. But scientists have now discovered that the eruption also triggered an unexpected atmospheric reaction that partially removed methane, a potent greenhouse gas, from the air. Researchers say the finding could eventually help scientists develop new strategies to slow global warming. Using satellite observations, scientists detected unusually high levels of formaldehyde inside the enormous volcanic plume created by the eruption. That discovery immediately caught their attention because formaldehyde is produced when methane breaks down in the atmosphere. "When we analyzed the satellite images, we were surprised to see a cloud with a record-high concentration of formaldehyde. We were able to track the cloud for 10 days, all the way to South America.…