The ozone layer or ozone shield is a region of Earth’s stratosphere that absorbs most of the Sun’s ultraviolet radiation. In 1974 two chemistry professors, Frank Rowland and Mario Molina, predicted that chlorofluorocarbons (CFCs), a set of chemicals used in refrigeration, would gradually decompose, release chlorine into the stratosphere and break down the ozone layer which protects Earth from ultraviolet radiation. The chairman of DuPont, a chemical company, called their idea “a load of rubbish”. Eleven years later, scientists discovered a hole in the ozone layer over Antarctica, and two years after that governments negotiated an agreement, the Montreal protocol, to phase out CFCs. Messrs Rowland and Molina now share a Nobel prize. Expanding the Montreal protocol would not, by itself, keep the rise in global temperatures within safe bounds. That will require cutting carbon emissions by around 26 billion tonnes of CO₂ equivalent a year by 2030 (or almost halving the current rate of emissions). A broad carbon treaty will still be necessary; so will stopping deforestation, slashing subsidies to fossil fuels and much else. But expanding the Montreal protocol would get more than a tenth of the way towards what is needed. More important, it can be agreed, and implemented, quickly, (‘Greenhouse gases–Paris via Montreal: The quickest way to cut greenhouse gases is to expand the Montreal protocol,’ The Economist 20th Sept 2014, p.14).