Ozonedepleting

Ozone depletion refers to the thinning of the stratospheric ozone layer, which protects life from a significant portion of the Sun’s ultraviolet radiation. The ozone layer absorbs most UV-B radiation, and reductions in ozone can increase surface UV exposure with health and ecological risks.

Most ozone depletion is caused by anthropogenic ozone-depleting substances (ODS) that release chlorine and bromine radicals in the stratosphere. Key examples include chlorofluorocarbons (CFCs), halons, carbon tetrachloride, methyl chloroform, methyl bromide, and related fluorinated and brominated compounds such as hydrochlorofluorocarbons (HCFCs). These substances are long-lived; when they reach the upper atmosphere, UV light frees halogen atoms that catalytically destroy ozone molecules in periodic cycles, leading to net ozone loss.

Beyond health effects such as increased skin cancer, cataracts, and immune suppression, ozone depletion can affect ecosystems, agricultural productivity, and climate-related processes. The most dramatic losses occur in polar regions, where annual ozone holes have been observed, though global ozone levels can also be affected.

Policy responses culminated in the Montreal Protocol of 1987, with later amendments to accelerate phaseouts of ODS. The treaty has led to declines in atmospheric chlorine and bromine and is widely regarded as a successful international environmental agreement. As a result, ozone is slowly recovering, with projections suggesting a return to 1980-level protection over coming decades, though timelines vary by region and substance lifetime.