Recent adjustments to the Montreal Protocol help protect ozone layer, but newer chemicals contribute to warming
An international agreement in 2007 to deal with the last remaining ozone-depleting chemicals used in large quantities is working, according to a new analysis published today. Atmospheric emissions of those chemicals, called hydrochlorofluorocarbons (HCFCs) and used in refrigeration and air conditioning, are no longer increasing, after having increased consistently over the past few decades, according to NOAA measurements published in the Journal of Physical Chemistry. But the new paper also reports that other substitute chemicals, which are also greenhouse gases, are on the rise, and international decision makers are considering new regulations to cap and reduce those emissions.
“NOAA monitors the composition of Earth's atmosphere closely, and it's that long-term, highly precise monitoring that lets scientists see clear evidence of slowing HCFC emissions since 2007, coincident with the adjustment to the Montreal Protocol,” according to Stephen Montzka, a scientist at ESRL's Global Monitoring Division in Boulder, Colorado, and the study’s lead author. For more on NOAA’s global sampling network, see sidebar.
Last fall, a scientific assessment report for the Montreal Protocol presented further evidence that the international agreement to protect Earth’s ozone layer is working, and that abundances of most ozone-depleting substances in the atmosphere are decreasing. The new paper describes progress in phasing out the last group of ozone-depleters used in significant quantities: HCFCs, which are first-generation replacements for other, more ozone-damaging chemicals initially targeted by the Montreal Protocol.
In 2007, the Montreal Protocol parties agreed to an accelerated schedule for the global phase-out of HCFCs. Although HCFC use in developing countries could have continued until 2040, the prospect that an accelerated phaseout would reduce future ozone depletion and slow climate change in the coming decades prompted the new limits.
This study presents evidence that the recent accelerated phase-out has helped slow global emissions of HCFCs, but it also documented a 45-percent increase in emissions of chemicals used as HCFC substitutes. That’s an important finding, because while these second-generation substitutes, called hydrofluorocarbons, don’t deplete ozone as HCFCs do, many are potent greenhouse gases and contribute to warming, in amounts that are currently small but could become significant in the future.
The study also examined sources of hydrofluorocarbon emissions, finding that global emissions of these chemicals can be attributed in roughly equal amounts to mobile air conditioning, commercial refrigeration, and all other uses (including solvents and industrial refrigeration) combined. This means, says Montzka, that hydrofluorocarbons currently used in car air conditioners contribute substantially to the overall climate impact of this group of chemicals. And while hydrofluorocarbons don’t have a big impact on warming right now, if demand for these chemicals continues to rise, especially in developing countries, those emissions could account for a significant proportion of global greenhouse gases in the future.
That finding has implications for policy decisions. “We’ve identified how much the different sectors contribute to hydrofluorocarbon emissions,” Montzka says. “This information might help policy makers decide how to reduce emissions more effectively.” For a number of years, parties to the Montreal Protocol have been considering a proposal to cap and reduce hydrofluorocarbons because they contribute to warming.
This paper also shows how policy has influenced atmospheric composition, allowing scientists to see how the 2007 adjustment to the Montreal Protocol, along with other factors, has played out in the atmosphere, says Montzka. David Fahey, director of ESRL's Chemical Sciences Division, and one of the paper’s co-authors, agreed. “NOAA’s global atmospheric sampling network provides key environmental intelligence that helps inform global policy and determine the effectiveness of policies controlling greenhouse gases and ozone-depleting substances,” says Fahey.
Today’s paper is part a special edition of the Journal of Physical Chemistry dedicated to renowned ozone hole scientist Mario Molina.
This research was made possible as a result of a collaboration between NOAA and CIRES scientists, DuPont Chemicals, and the Institute for Governance and Sustainable Development.
Authors of, “Recent Trends in Global Emissions of Hydrochlorofluorocarbons and Hydrofluorocarbons: Reflecting on the 2007 Adjustments to the Montreal Protocol” are: Stephen Montzka (NOAA and CIRES), Mack McFarland (DuPont Chemicals & Fluoroproducts), Stephen O. Andersen (Institute for Governance & Sustainable Development), Benjamin Miller (CIRES and NOAA), David Fahey (NOAA), Bradley Hall (NOAA), Lei Hu (CIRES and NOAA), Carolina Siso (CIRES and NOAA), and James W. Elkins (NOAA)