The Montreal Protocol — a 1987 international agreement to end production of ozone-destroying chemicals like freon — seems miraculous compared to the long struggle to achieve meaningful action on climate change. Even more amazingly, the agreement has worked. Those chemicals (known as CFCs) take a long time to flush from the atmosphere, but monitoring has shown that the flush is largely going according to plan.
That keeps the hole in the ozone layer on track to shrink in the coming decades. However, a new study finds that someone has been cheating in recent years.
A group of researchers led by Stephen Montzka of the US National Oceanic and Atmospheric Administration had been monitoring the progress of CFCs and noticed something with CFC-11. This chemical has been used as a refrigerant, solvent, and propellant for aerosol cans, as well as in the manufacture of Styrofoam. As with the other CFCs, the countries agreed to end production of CFC-11 entirely. While there may still be older machines leaking CFC-11, these sources should gradually disappear over time, which could accelerate the decline in atmospheric concentration.
Hide the drop?
Instead of an accelerating decline, CFC-11 showed a steady decline of 2.1 parts per trillion per year between 2002 and 2012. Since then, the decline delayed. Between 2015 and 2017, CFC-11 declined by just 1.0 part-per-trillion per year.
There are a few possible explanations to sort through. The most important are natural variations in the transport of emitted CFCs to the stratosphere, which is dependent on weather patterns. But some can be eliminated quickly. For example, a sudden uptick in the demolition of old buildings with CFC-11 refrigerants in their HVAC systems doesn’t seem plausible to fit the data.
Careful analysis of the data and some modeling can help us make a choice from the other explanations. First, the concentration of these gases in the Northern Hemisphere has always been slightly higher than in the Southern Hemisphere, because most of the sources are in the North. In recent years, the difference between the two hemispheres has widened slightly. Similar gases have not, indicating increased emissions from the Northern Hemisphere rather than just a change in wind.
Second, measurements from the top of Mauna Loa in Hawaii show correlations between CFC-11 concentrations and a few other gases known to come from industrial emissions. That means CFC-11 isn’t the only human pollutant to see a rise in the same time span.
Finally, the researchers used some models to find out what types of emissions would fit the pattern of measurements around the world. Modeling of weather patterns since 2000 shows that natural variability in atmospheric circulation could explain part of the changing trend, but less than half. The measurements can really only be explained by an increase in emissions from East Asia.
A new source
At the peak of use in the 1980s, people released 350,000 tons of CFC-11 each year — a number that dropped to 54,000 tons per year in the early 2000s. An additional 6,500 to 13,000 tons released each year in East Asia would be enough to change the downward trend in the way we have observed. Such a large increase seems to require a re-production of CFC-11, which is in violation of the Montreal Protocol.
“This is the first time emissions of one of the three most abundant, long-lived CFCs have increased for a sustained period since production controls came into effect in the late 1980s,” the researchers write. “A delay in ozone recovery […] is expected, with a public interest depending on the trajectory of CFC-11 emissions and concentrations in the future.”
Given that countries are required to monitor CFC production and report accurate figures to the United Nations’ group overseeing the Montreal Agreement, this becomes a controversial conclusion. The researchers chose their words carefully and the network of measurements is not complete enough to point the finger at a specific country. Still, the list of suspects is short and a country must track down and eradicate illegal industrial activity within its borders to enforce the end of the Montreal Protocol.
Nature2018. DOI: 10.1038/s41586-018-0106-2 (About DOIs).