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What is the concentration of CFCs in the atmosphere, and how much do they contribute to global warming?

Chlorofluorocarbons, or CFCs, make up just four parts per billion of the atmosphere, but they're so efficient at warming the planet that they’re still an important contributor to climate change.

 

February 13, 2023

Carbon dioxide (CO2) is the most well-known and significant greenhouse gas causing climate change. But there are others, including methane, nitrous oxide—and chlorofluorocarbons (CFCs). CFCs were developed in the late 1920s to replace toxic compounds used in refrigeration and air conditioning; they have also been used in aerosols and as solvents. And while they’ve never been nearly as abundant as CO2, these compounds are much more potent at trapping heat in the atmosphere.

Greenhouse gases warm the earth by absorbing infrared radiation, light invisible to the human eye but important to our planet because it’s how the Earth gives off heat. By intercepting this light as it makes its way out to space, these gases keep more heat energy in our atmosphere. Different greenhouse gases absorb this radiation at different wavelengths of the infrared spectrum.

Chemical bonds in CFC molecules, particularly the carbon-chlorine and carbon-fluorine bonds, are very efficient at absorbing this infrared radiation. CFCs also absorb light in a part of the infrared spectrum that more abundant greenhouse gases like CO2 and water vapor do not. By capturing that heat that would otherwise escape into space, even a small amount of CFC molecules can have a significant impact on warming. And CFCs can also last a long time in the atmosphere because they don’t react readily with other compounds, only sunlight.

“They have a very large global warming potential,” says Kane Adam Stone, a research scientist at MIT who studies radiative-chemical processes. “Some of these molecules can have global warming potentials of thousands to, in some cases, tens of thousands of times more than CO2.”

“Global warming potential” (GWP) measures a greenhouse gas’s ability to trap heat for 100 years. Carbon dioxide has a global warming potential of one, and other greenhouse gases are measured against it: so methane, which has a GWP of about 25, traps roughly 25 times as much heat over 100 years. There are different types of CFC molecules, but because they are so good at trapping heat and they stick around for so long, their global warming potentials are between about 4,750 and 14,400.1

Those high warming potentials mean that the contribution of CFCs and related chemicals to climate change is “quite substantial,” says Stone: about 16 percent that of our CO2 emissions.2 And that’s true even though the amount of carbon dioxide in the atmosphere—about 420 parts per million—is over 10,000 times higher than that of CFCs (which have an atmospheric concentration of just four parts per billion).

CFCs were banned in the 1980s under an international agreement called the Montreal Protocol—not because of climate change, but because they also have a significant impact on the ozone layer that protects us from harmful ultraviolet radiation. As CFCs break down, their chlorine atoms are set loose in the atmosphere, where they break apart ozone molecules. One chlorine atom alone can damage more than 100,000 ozone molecules, according to the U.S. Environmental Protection Agency.3

Despite their phaseout, it’s important to understand the warming impact of CFCs, because those we’ve already manufactured will be with us for a long time. The molecules can persist in the atmosphere for between 55 and 140 years,4 and the chemicals are present in old machinery that’s still being disposed of.

 

Thank you to David Liston of France for the question. You can submit your own question to Ask MIT Climate here.

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Footnotes

1 Intergovernmental Panel on Climate Change: Direct Global Warming Potentials. From IPCC Fourth Assessment Report: Climate Change 2007: The Physical Science Basis.

2 World Meteorological Organization: Executive Summary, Scientific Assessment of Ozone Depletion: 2022. This figure includes the global warming contributions of replacements for CFCs like hydrochlorofluorocarbons (HCFCs). Additional figures from the U.S. Environmental Protection Agency show that just the two most common CFCs, CFC-12 and CFC-11, are today warming the Earth about 10% as much as our CO2 emissions to date. U.S. Environmental Protection Agency: Climate Change Indicators: Climate Forcing. Accessed February 13, 2022.

3 U.S. Environmental Protection Agency: Basic Ozone Layer Science.

4 National Oceanic and Atmospheric Administration Global Monitoring Laboratory: Chlorofluorocarbons (CFCs). From The Chapman & Hall Encyclopedia of Environmental Science, ed. David E. Alexander and Rhodes W. Fairbridge, Kluwer Academic, Boston, Mass., 1999.