Unless the problem is isolated and rectified, the discovery of a rise in CFC-11 could put the recovery of the vital atmospheric shield in jeopardy for at least a decade.
The source has been tracked to east Asia, but narrowing down the precise location will require further investigation.
CFC chemicals were used in numerous products, from the foams in furniture to aerosols and refrigerants.
However, they were banned under the global Montreal protocol after they were blamed for a huge hole in the ozone layer over Antarctica which was discovered in the 1980s.
CFC-11, the second-most damaging of all CFCs, has not been produced anywhere in the world since 2007 – making the discovery of a 25 per cent rise in global emissions all the more baffling.
Stephen Montzka, at the US National Oceanic and Atmospheric Administration (NOAA) in Colorado, who along with colleagues made the discovery, said. “I have been doing this for 27 years and this is the most surprising thing I’ve ever seen.
“I was just shocked by it. We are acting as detectives of the atmosphere, trying to understand what is happening and why
“When things go awry, we raise a flag.”
Erik Solheim, head of UN Environment, added: “If these emissions continue unabated, they have the potential to slow down the recovery of the ozone layer.
“It’s therefore critical that we identify the precise causes of these emissions and take the necessary action.”
Work undertaken so far by Mr Montzka and his fellow scientists has ruled out natural processes which could explain the rise in the level of emissions.
He added: “It really looks like somebody is making it new.
“If the increased emissions were to go away [soon], it’s influence on the recovery date for the ozone layer would be minor.
“If it doesn’t go away, there could be a 10-year delay, and if it continued to increase, the delay would be even longer.”
He said the last option was a distinct possibility, because if the new CFC-11 was being used in foams, then only a small fraction will have made it to the atmosphere so far.
Michaela Hegglin, from the University of Reading, said: “The study highlights that environmental regulations cannot be taken for granted and must be safe-guarded, and that monitoring is required to ensure compliance.”
Meanwhile Lancaster University’s Paul Young added: “The Montreal Protocol has been rightly hailed as our most successful international environmental treaty, so the suggestion that there are possibly continued, unreported emissions of CFCs is certainly troubling and needs further investigation.”