Earth’s protective ozone layer is on a path to recover in the next 35 years from depletion by industrial chemicals, a new United Nations report says. But it warns that the climate benefits achieved by the global phaseout of ozone-depleting substances may be eliminated by emissions of ozone-friendly replacement compounds that are powerful greenhouse gases. Ozone in the upper stratosphere is on track to return to its 1980 levels by mid century, the report says. Stratospheric ozone levels fell between 1979 and 1997 and have risen since 2000 because of international action to phase out the production and use of chemicals under the Montreal Protocol on Substances That Deplete the Ozone Layer. Many of these ozone-destroying compounds are also greenhouse gases, so elimination of them has offset some human-caused climate change, the report says. But these substances have been replaced in many applications by hydrofluorocarbons, which don’t directly harm ozone but are potent greenhouse gases. If the use of HFCs goes unchecked, emissions of these substances, which are rising at a rate of 7% annually, could wipe out the climate gains achieved by the Montreal protocol, the report says.