The infamous hole in Earth’s ozone layer has shrunk down to 7.6 million square miles wide (12,200,000 square kilometers), the smallest the gap has been since 1988. This healing of Earth’s main shield against ultraviolet radiation is due largely to efforts initiated in the mid-1980s, when the use of ozone-harming CFCs was phased out. Not only is this positive news in regards to our atmosphere’s ability to filter out harmful UV radiation, it also stands as an example of how humanity can make a positive, large-scale impact when efforts to reduce ecological harm are required, such as in the case of our need to reduce greenhouse gas emissions.

The Earth’s ozone layer is found in the stratosphere at an altitude of 20 to 30 kilometers (12 to 19 miles), and is host to concentrations of ozone of approximately 10 parts per million, quite high when compared to the 0.3 ppm found near the surface. Ozone is a molecule that consists of three oxygen atoms (O3), that when struck by ultraviolet rays is split into an ordinary oxygen molecule (O2) and a lone oxygen atom. The rogue oxygen atom eventually recombines with another O2 molecule to form a new ozone molecule, allowing the cycle to continue.

This cycle is disrupted by the presence of atoms such as bromine and chlorine, elements that are readily available in chlorofluorocarbons (CFCs) — hence the discontinuation of their use in applications such as aerosol propellants and refrigerants. In the late 1970s, CFCs were found to be depleting stratospheric concentrations worldwide, although the depletion of the ozone layer was dramatically worse over the Earth’s polar regions, with the depleted region in the south becoming known as the "ozone hole".

Unfortunately, ozone production was aided by temperatures in the stratosphere that were warmer than usual, part and parcel of the record-breaking temperature records experienced in 2016. "Weather conditions over Antarctica were a bit weaker and led to warmer temperatures, which slowed down ozone loss," explains Paul A. Newman, chief Earth scientist at NASA’s Goddard Space Flight Center. "It’s like hurricanes. Some years there are fewer hurricanes that come onshore . . . this is a year in which the weather conditions led to better ozone [formation]."

Although the issue of reducing humanity’s greenhouse gas emissions is in many ways more complex, the healing of the ozone layer offers an example of what we can accomplish if a concerted effort is put into reducing large-scale ecological harm. Much like the Paris accord, the Montreal Protocol (the name of the international agreement to reduce CFC use) was eventually signed by all 197 countries on the planet, and set similar goals into reducing the output of the offending chemicals.