FILE - A boat navigates next to a large iceberg in eastern Greenland on Aug. 15, 2019. Even if the world somehow manages to limit future warming to the strictest international temperature goal, four Earth-changing climate “tipping points” are still likely to be triggered like the irreversible collapse of the Greenland ice sheets, with a lot more looming as the planet heats more after that, a new study said. (AP Photo/Felipe Dana, File)