Earth's protective ozone layer, on a slow path to recovery since the 1987 Montreal Protocol banned chemicals that erode it, may be in danger anew, scientists warned on Tuesday. Levels in the stratosphere of dichloromethane, a chemical not covered by the ozone rescue pact, are increasing rapidly and could delay the layer's recovery, they said.
Although "currently modest, the impact of dichloromethane on ozone has increased markedly in recent years," a team reported in the journal Nature Communications. "Sustained growth in dichloromethane would... offset some of the gains achieved by the Montreal Protocol, further delaying recovery of Earth's ozone layer."
The layer sits in the stratosphere at 10 to 50 kilometres (six to 30 miles) above the Earth's surface, where it filters out harmful ultraviolet light that can cause cancer and damage crops. The Montreal accord phased out production of chlorofluorocarbons (CFCs) in refrigerators, aerosols, air-conditioners and foam insulation when it was discovered they were responsible for the so-called ozone "hole".
CFCs were replaced in the 1990s by hydrofluorocarbons (HFCs), which were safe for the now-healing ozone but also highly effective at trapping heat in the atmosphere, contributing to global warming. An amendment to the pact, to phase out HFCs, was signed in Kigali in February.
Scientists have already raised concern about the potential ozone impact of manmade chemicals called "very short-lived substances" or VSLS, such as dichloromethane. VSLS gases usually break down in less than six months. The new study sought to quantify the harm threatened by dichloromethane, which is used as a solvent in paint strippers and as a degreaser, and also to decaffeinate coffee.