A SLOW HEALING

Global action is mending the ozone layer, but unregulated short-lived chlorinated emissions by industries are delaying full recovery

- RAJIT SENGUPTA NEW DELHI

FOUR DECADES of international action to ban chlorofluorocarbons (CFCS) have put the Antarctic ozone hole on a demonstrable path to recovery. Yet the win is partial, suggest two recent studies. One of the studies, led by the Massachusetts Institute of Technology, US, shows for the first time with high statistical confidence that the recovery owes overwhelmingly to declines in CFCs, a group of human-made long-lived ozone-depleting substances once widely used as refrigerants, propellants and solvents. The other study, by a group of researchers in Canada and the UK, identifies an obstacle to a faster rebound: increasing emissions of chlorinated very-short-lived substances (CL-VSLS) that are topping up stratospheric chlorine. CL-VSLS are chlorine containing gases used in solvents and industrial processes that have short atmospheric lifetimes of around six months. The two studies together suggest that the ozone layer is healing because of human action, yet human activity is also nudging the recovery off course.

Ozone is a naturally occurring gas within the Earth's stratosphere that acts as a sort of sunscreen, protecting the planet from the sun's harmful ultraviolet radiation. In 1985, scientists discovered a “hole” in the ozone layer over Antarctica that opened up between September and December. This seasonal ozone depletion was suddenly allowing UV rays to filter down to the surface, leading to skin cancer and other adverse health effects.