This combination of July 1998 and April 2020 photos shows a difference in smog levels above the Los Angeles skyline, with California Highway 110 in the foreground. With climate change, plastic pollution and a potential sixth mass extinction, humanity has made some incredible messes in the world. But when people, political factions and nations have pulled together, they have also cleaned up some of those human-caused environmental problems. (AP Photo/Nick Ut, Marcio Jose Sanchez)