Chemicals banned from air conditioners and refrigerators are making a comeback — and scientists don’t know why

In this image from September 2006, the Antarctic ozone hole measured 11.4 million square miles (29.5 million square kilometers). | Image: Universal History Archive/ Universal Images Group via Getty Images

Chemicals that were banned after they punched a hole in Earth’s ozone layer are still building up at an alarming rate in our atmosphere, according to research published today in the journal Nature Geoscience. The chemicals were once widely used in air conditioning and refrigeration but were supposed to be phased out globally by 2010.

Scientists were surprised to find that concentrations of several types of those chemic...