Stratospheric ozone 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 climate benefits from the global phaseout of ozone-depleting substances may be eliminated by emissions of ozone-friendly replacement compounds that are potent greenhouse gases.
“It is particularly gratifying to report that the ozone layer is on track for recovery to 1980 benchmark levels by midcentury,” said Paul A. Newman, chief scientist for atmospheres at the National Aeronautics & Space Administration (NASA) Goddard Space Flight Center, in Greenbelt, Md. Stratospheric ozone levels fell between 1979 and 1997 and have risen since 2000, notes Newman, who cochaired the scientific panel that wrote the report published by the UN Environment Programme and the World Meteorological Organization. Hundreds of scientists compile the report every three to four years under a UN treaty, the Montreal Protocol on Substances That Deplete the Ozone Layer.
Through that accord, all of the nearly 200 countries that are members of the UN are eliminating production and use of ozone-depleting compounds such as chlorofluorocarbons and halons. The healing of the ozone layer is a direct result of this effort, the report says.
Many of these ozone-destroying chemicals 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, including in car air conditioners, by hydrofluorocarbons.
HFCs don’t directly harm ozone but are potent greenhouse gases. They have a higher potential to cause global warming than the substances they replace. If the use of HFCs goes unchecked, emissions of these substances could wipe out the climate gains achieved as a side benefit of the Montreal protocol, the report says.
Current annual HFC emissions have the same global warming potential as 0.5 gigatons of carbon dioxide, according to the report. Global HFC releases are increasing about 7% per year.
Emissions of HFCs are growing faster than any other greenhouse gas, including carbon dioxide, in many countries, including the U.S., China, and India, according to the Institute for Governance & Sustainable Development.