Officially, the production of CFC-11 should be near zero or nearly zero - at least, those are the countries that cooperate with the United Nations body that monitors and ensures compliance with the Montreal Protocol.
The scientists say that the increase is likely a result of new, unreported production of the gas, known as CFC-11, probably in East Asia.
"Knowing how much time and effort and resources have gone into healing the ozone layer and to see this is a shocker, frankly", Montzka said.
The UNEP said that is was "critical that we take stock of this science, identify the causes of these emissions and take necessary action".
Given that the boost in output will inevitably slow the planet's ozone layer recovery, discovering the source of the new production would seem an urgent priority.
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"It is not clear why any country would want to start to produce, and inadvertently release, CFC-11, when cost-effective substitutes have been available for a long while", Watson continued. This means that the total concentration of ozone-depleting chemicals, overall, is still decreasing in the atmosphere. But the apparent increase in emissions of CFC-11 has slowed the rate of decrease by about 22 percent, the scientists found. Then, surprisingly, the rate of decline hardly changed over the decade that followed. After considering a number of possible causes, Montzka and his colleagues concluded that CFC emissions must have increased after 2012.
Image The largest ever spotted ozone hole over Antarctica. Pic NASA
Measurements from Hawaii indicate the sources of the increasing emissions are likely in eastern Asia.
The USA ceased production in 1996 and other countries agreed to phase out CFC production by 2010.
As a result of the controls, CFC11 concentrations have declined by 15% from peak levels measured in 1993. More work will be needed to narrow down the locations of these new emissions, Montzka said.
Emissions of CFC-11 increased by 25 percent in 2012, despite the fact that the chemical substance is part of a group of pollutants for ozone, which were banned under the Montreal Protocol of 1987.
To put that in perspective, production of CFC-11, marketed under the trade name Freon, peaked at about 430,000 tons per year in the 1980s. He calls it "rogue production", adding that if it continues "the recovery of the ozone layer would be threatened". "But this is most surprising one".
"If the increased emissions were to go away [soon], it's influence on the recovery date for the ozone layer would be minor", he said.
The Montreal Protocol, signed by more than 200 countries and generally regarded as having a good record of compliance, is created to protect the Earth's ozone layer.
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