The ozone depletion hypothesis is still scientifically contested. CFC chemicals may or may not be responsible.

The connection between chlorofluorocarbons and atmospheric ozone was first proposed as a theoretical possibility in 1974, in a paper by F. Sherwood Rowland and Mario Molina published in Nature. The chemistry was not obscure: CFC molecules, used extensively in refrigerants, aerosol propellants, and foam-blowing agents, were stable enough at ground level to drift intact into the stratosphere, where ultraviolet radiation broke them apart and released chlorine atoms. Each chlorine atom could destroy thousands of ozone molecules in a catalytic chain reaction, thinning the stratospheric layer that blocked UV-B radiation from reaching Earth’s surface.

The chemical industry’s response was immediate and well-funded. DuPont, Allied Chemical, and their trade associations challenged the science through lobbying campaigns, funding alternative research, and directly lobbying regulatory agencies. Their argument was that the ozone depletion hypothesis was theoretical and unproven, no one had measured a hole, only modelled a risk. By the time students were studying atmospheric chemistry in high school through the mid-1980s, the question was often presented as genuinely contested: some scientists thought CFCs were dangerous, others didn’t, and the evidence was unclear.

The evidence became impossible to dispute in May 1985. British Antarctic Survey scientists Joe Farman, Brian Gardiner, and Jonathan Shanklin published measurements showing that total ozone over Halley Bay had fallen by more than 40 percent since the 1970s, a finding so dramatic it initially seemed like instrument error. NASA’s satellite data confirmed it: a vast seasonal ozone hole had opened over Antarctica each southern spring. The hole was not a theoretical risk. It was already there.

Negotiations moved with unusual speed. The Montreal Protocol was signed in September 1987, committing signatory nations to phase out CFC production on a defined schedule. It was later strengthened repeatedly, the phase-out accelerated and the list of controlled substances expanded. Today the ozone layer is recovering; the hole has been shrinking since roughly 2000, and full recovery is projected by the middle of the twenty-first century. Rowland and Molina received the Nobel Prize in Chemistry in 1995. The Montreal Protocol is widely cited as one of the most successful international environmental agreements in history, a rare demonstration that coordinated action could halt and reverse an atmospheric crisis.