Scientists have some good news about the ozone layer as recovery continues this year.

The concentration of ozone-depleting chemicals in the stratosphere over the mid-latitudes, where many of the globe’s humans live, continues to drop. The levels of chemicals have dropped to 50% of the levels observed in 1980.

The recovery over Antarctica, where large ozone holes occurred last spring, has been slower. The level of ozone-depleting chemicals in the stratosphere has only dropped 26% from 1990 levels and a full recovery isn’t expected until 2070. The Antarctic is slow to recover due to cold temperatures and global air circulations.

Stratospheric ozone, a highly reactive chemical situated high in the atmosphere, protects the globe from dangerous ultraviolet radiation from the sun.

Man-made chemicals containing chlorine, bromine, and fluorides used as refrigerants, solvents, and propellants, were found to react with the ozone in 1980s. A global treaty, the Montreal Protocol, has phased out the manufacturing of these chemicals since 1989.

However, these chemicals, once they make it into the stratosphere, can take years or decades to decay, reacting with ozone along the way. This will keep the rate of ozone recovery slow.