That's the assessment some 300 scientists have offered to countries who are party to the 1987 Montreal Protocol and related agreements – the latest in a series of quadrennial reports on the state of the planet's stratospheric ozone.
The protocol bans the production of chlorine- and bromine-based gases such as chlorofluorocarbons and halons, once widely used for tasks ranging from refrigeration and launching deodorant from spray cans to fire suppression. Overall, about 100 chemicals are covered under the protocol. Recommended: Are you scientifically literate? Take our quiz
Once these gases reach the atmosphere, they persist for decades to be lofted into the stratosphere, where they break up ozone molecules. These molecules – made of of three oxygen atoms – absorb the most biologically damaging form of ultraviolet radiation that reaches Earth from the sun.
The protocol's goal is to restore stratospheric ozone concentrations to 1980 levels by around 2050, following a steep decline between 1960 and the early 1990s at latitudes spanning the globe from Stockholm to the Southern Ocean. Stratospheric-ozone concentrations bottomed out over Antarctica around 2000 in a feature that became known as the continent's ozone hole.
Although overall ozone levels had dropped 3 to 4 percent by the time the brakes on ozone-depleting chemicals took hold, concentrations of these chemicals could have risen 10 times by 2050, triggering substantial further decline.
Now, mid-latitude ozone concentrations are expected to reach 1980 levels between 2040 and 2060.
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