David Doniger, director of the climate and clean energy program of the Natural Resources Defense Council, an environmental group in Washington, said the new emissions were "bad for the ozone layer and bad for climate change".
"We show that the rate of decline of atmospheric CFC-11 was constant from 2002 to 2012, and then slowed by about 50 percent after 2012", an worldwide team of scientists concluded in a study.
Unless the culprit is found and stopped, the recovery of the ozone layer, which protects life on Earth from damaging UV radiation, could be delayed by a decade. A smaller amount of CFC-11 also exists today in chillers. But they were banned under the global Montreal protocol after the discovery of the ozone hole over Antarctica in the 1980s. A research letter published Wednesday in the journal Nature takes a look at the possible causes for the spike.
They considered a range of alternative explanations for the growth, such as a change in atmospheric patterns that gradually remove CFC gases in the stratosphere, an increase in the rate of demolition of buildings containing old residues of CFC-11, or accidental production. Rather, the evidence "strongly suggests" a new source of emissions, the scientists wrote.
The UNEP said that is was "critical that we take stock of this science, identify the causes of these emissions and take necessary action".
"The reduction in the atmospheric concentration of trichlorofluoromethane (CFC-11) has made the second-largest contribution to the decline in the total atmospheric concentration of ozone-depleting chlorine since the 1990s", the new research says.
CFC-11, used primarily for foams, can last up to 50 years in the atmosphere once it is released.
"The ozone layer remains on track to recovery by mid-century", the UN Environment Programme (UNEP) said in a statement, reacting to the findings.
The researchers show that CFC-11 levels, measured at a number of remote monitoring sites around the world, decreased in line with expectations between 2002 and 2011. "It is therefore imperative that this finding be discussed at the next Ministerial meeting of Governments given recovery of the ozone layer is dependent on all countries complying with the Montreal Protocol (and its adjustments and amendments) with emissions globally dropping to zero". Scientists say there's more of it - not less - going into the atmosphere and they don't know where it is coming from.
The Montreal Protocol has been effective in reducing ozone-depleting gases in the atmosphere because all countries in the world agreed to legally binding controls on the production of most human-produced gases known to destroy ozone.
But "continued increase in global CFC-11 emissions will put that progress at risk".
If the source of these emissions can be identified and mitigated soon, the damage to the ozone layer should be minor.