Cleaner Earth: Healing ozone hole, less smog, more eagles

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, including healing the ozone hole, clearing perpetually smoggy air and saving many species from the brink of extinction.

“We can be good at cleaning up our messes, it’s whether or not we choose to be and what we prioritize,” said Michigan State University environmental sustainability researcher Sheril Kirshenbaum.

For Earth Day, The Associated Press asked more than 25 environmental scientists and policy experts, including two former U.S. Environmental Protection Agency chiefs and the current director of the United Nations Environment Programme, to share their top stories about environmental problems that the world fixed.

“There are some amazing success stories,” said Stanford University environmental scientist Rob Jackson. “It’s easy for us to get tunnel vision with everything going wrong, and there is a lot that needs to change quickly. But it’s wonderful to remind ourselves that other people in the past have succeeded and that society has succeeded too, both nationally here in the U.S. and also internationally.”

Here are the four successes mentioned most often and a key aspect that so many ecological wins have in common.

HEALING THE OZONE HOLE

Fixing ozone depletion was by far the top choice of scientists, officials and environmental policy experts.

“It was a moment where countries that usually compete with each other grasped the collective threat and decided to implement a solution,” former EPA chief Carol Browner said in an email.

Scientists in the 1970s had discovered that a certain class...