CFC-11 emissions have increased by 25 percent since 2012, despite the fact that the chemical is part of a group of ozone pollutants that were eliminated under the 1987 Montreal Protocol.
" I've been doing these measurements for over thirty years and this is the most amazing thing I've seen, "said Stephen Montzka, a scientist with the National Oceanic and Atmospheric Administration (ONA) who led the work. "I was really amazed"
It is an anguishing result for what is considered a global environmental success story, in which nations, alarmed by a growing "ozone hole", took collective measures to phase out chlorofluorocarbons.  The finding seems to trigger an international investigation into this mysterious source.
Officially, it is assumed that the production of CFC-11 is close or zero; At least, that is what the countries have been saying to the UN agency that monitors and enforces the Protocol. But with the emissions increasing, scientists suspect that someone is manufacturing the chemical in defiance of the ban.
"Someone is cheating," said Durwood Zaelke, founder of the Institute for Governance and Sustainable Development and an expert on the Montreal Protocol, in a commentary on the new research. "There is a small possibility that there is an involuntary release, but … they make it clear that there is strong evidence that it is actually happening."
But for now, scientists do not know exactly who, or where, that person is. A US observatory in Hawaii found that CFC-11 was mixed with other gases that were characteristic of a source from somewhere in East Asia, but scientists could not reduce the source further.
Zaelke said he was surprised by the findings, not only because the chemical has been banned for a long time, but also because alternatives already exist, which makes it difficult to imagine what the CFC-11 market would be today.
The research was conducted by researchers from the US National Oceanic and Atmospheric Administration. UU with the help of scientists in the Netherlands and the United Kingdom. Their results were published in the journal Nature.
There is a small possibility that there is a more innocent explanation for the increase in CFC-11 emissions, says the scientist.
Considered a variety of alternative explanations for growth, such as a change in atmospheric patterns that phase out CFC gases in the stratosphere, an increase in the rate of demolition of buildings containing old CFC-11 waste, or production accidental.
But they concluded that these sources could not explain the increase, which they calculated at around 13 billion grams per year in recent years. Rather, the evidence "strongly suggests" a new source of emissions, the scientists wrote.
"These considerations suggest that the highest emissions of CFC-11 arise from new production not reported to the UNEP Ozone Secretariat, which is inconsistent with the agreed phase" outside CFC production under the Montreal Protocol for 2010 ", the researchers wrote.
CFC-11, used mainly for foams, can last up to 50 years in the atmosphere once it has been launched, it is only destroyed in the stratosphere, between 9 and 18 miles above the surface of the planet, where the resulting chlorine molecules are involved in a chain of chemical reactions that destroy ozone, which, in turn, weakens our protection against UV radiation on the surface of the Earth.
The chemical it is also a powerful greenhouse gas that contributes to global warming.
The document's findings are "environmentally and politically quite serious," said Robert Watson, the former scientist. or from NASA, which organized reinforcement flights in the Antarctic stratosphere to study ozone depletion in the 1980s, in an email statement.
"It is not clear why a country would want to start producing, and inadvertently launching, CFC-11, when profitable substitutes have been available for a long time," continued Watson.
"Therefore, it is imperative that this finding be discussed at the next ministerial meeting of governments given the recovery of the ozone layer depends on all countries complying with the Montreal Protocol (and its adjustments and amendments) with emissions that fall globally to zero. "
Watson suggested that aircraft flights could be null. It is necessary to better identify the source of the emissions.
Keith Weller, spokesman for the United Nations Environment Program, which administers the Montreal Protocol, said the findings should be verified by the scientific panel of the Protocol, and then presented to the member countries of the treaty.
"If these emissions continue unabated, they have the potential to slow down the recovery of the ozone layer," Weller said in a statement. "Therefore, it is essential that we take stock of this science, identify the causes of these emissions and take the necessary measures."
The unreported production of CFC-11 outside certain specific purposes of exclusion in the treaty would be a "violation of international law," Weller confirmed, though he said the Protocol is "non-punitive" and that the remedy likely implies a negotiation with the infringing party or country.
But Zaelke thought the finding could promote tougher action.
"This treaty can not afford not to follow its tradition and maintain its record of compliance," he said.
"They are going to find the culprits, this insults everyone who has worked on this for the past 30 years, a difficult group of people."
In general, it is important to stress that the ozone layer is recovering slowly and ozone-depleting substances continue to decline. But the apparent increase in CFC-11 emissions has lowered the rate of decline by about 22 percent, the scientists found. This, in turn, will delay the recovery of the ozone layer and, in the meantime, leave it more vulnerable to other threats.
"Knowing how much time and effort and resources have gone into healing the ozone layer, and seeing this is a surprise, frankly," said Montzka.
Tale of Chris Mooney. Mooney covers climate change, energy and the environment. He has reported on the climate negotiations of Paris 2015, the Northwest Passage and the Greenland ice sheet, among other places, and has written four books on science, politics and climate change.