Banned by the Montreal Protocol in 1987, CFC-11 was seen to be declining as expected but that fall has slowed down by 50% since 2012.
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.
"We're raising the flag to say, look, this is not what we hope happens for the ozone layer", said Dr. Montzka, a research chemist at the Earth System Research Laboratory in Boulder, Colo., a part of the National Oceanic and Atmospheric Administration.
Emissions of one of the chemicals most responsible for the Antarctic ozone hole are on the rise, despite an worldwide treaty that required an end to its production in 2010, a new NOAA study shows.
The new study, published today in Nature, documents an unexpected increase in emissions of this gas, likely from new, unreported production.
The researchers built mathematical models to account for these observations, which suggest CFC-11 emissions have actually been increasing by around 25% each year since 2012, despite virtually no CFC-11 production being reported to the relevant authorities during this time. CFC can still be leaked when old refrigerators are scrapped, for example.
"If the emissions were to persist, then we could imagine that healing of the ozone layer, that recovery date, could be delayed by a decade", said Dr Montzka.
"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.
It's tough to narrow down a specific culprit, but the NOAA can make distinctions between emissions from the northern and southern hemispheres, and the sudden uptick in CFC-11 seems to be coming from the northern hemisphere.
CFCs and other molecules have mainly eroded ozone in the upper stratosphere, and over the poles.
Measurements from Hawaii indicate the sources of the increasing emissions are likely in eastern Asia.
The UNEP said that is was "critical that we take stock of this science, identify the causes of these emissions and take necessary action". This insults everybody who's worked on this for the last 30 years.
Unreported production of CFC-11 outside of certain specific carve-out purposes in the treaty would be a "violation of worldwide law", Weller confirmed, though he said that the Protocol is "non-punitive" and the remedy would probably involve a negotiation with the offending party, or country. "That's a tough group of people". But the apparent increase in emissions of CFC-11 has slowed the rate of decrease by about 22 percent, the scientists found. If not remedied soon, however, substantial delays in ozone layer recovery could be expected, Montzka said.
"The newer substances that are out there, the replacements for CFC-11, might be more hard or expensive for some countries to produce or get at".