There is a lot of confusion surrounding the role played by ozone in global climate change. I often encounter college students who conflate two very distinct problems: the hole in the ozone layer, and greenhouse gas-mediated global climate change. These two problems are not as directly related as many think. If ozone had nothing to do with global warming, the confusion could be cleared up simply and quickly, but unfortunately, a few important subtleties complicate the reality of these important issues.
What Is Ozone?
Ozone is a very simple molecule made up of three oxygen atoms (hence, O3). A relatively high concentration of these ozone molecules float around 12 to 20 miles above the surface of the Earth. That layer of widely scattered ozone plays a crucial role for life on the planet: it absorbs most of the sun’s UV rays before they reach the surface. UV rays are damaging to plants and animals, as they cause serious disruptions inside living cells.
A Recap of the Ozone Layer Problem
Several man-made molecules are a threat to the ozone layer. Most notably, chlorofluorocarbons (CFCs) were used in refrigerators, freezers, air conditioning units, and as the propellant in spray bottles. The usefulness of CFCs stems in part from how stable they are, but this quality also allows them to withstand the long atmospheric journey all the way up to the ozone layer. Once there, CFCs interact with the ozone molecules, breaking them apart. When sufficient amounts of ozone have been destroyed, the low concentration area is often called a “hole” in the ozone layer, with increased UV radiation making it to the surface below.
The 1989 Montreal Protocol successfully phased out CFC production and use. Are those holes in the ozone layer the main factor responsible for global warming? The short answer is no.
Fact #1: The thinning ozone layer does not result in significant increases in global temperatures
Ozone Damaging Molecules Play a Role in Climate Change
The story does not end here. The same chemicals that break down ozone molecules are also greenhouse gases. Unfortunately, that trait is not a sole characteristic of CFCs: many of the ozone-friendly alternatives to CFCs are themselves greenhouse gases. The extended family of chemicals CFC belongs to, halocarbons, can be blamed for approximately 14% of the warming effects due to greenhouse gases, behind carbon dioxide and methane.
Fact #2: Ozone-depleting chemicals also act as greenhouse gases.
At Low Altitudes, Ozone Is a Different Beast
Up to this point the story was relatively simple: ozone is good, halocarbons are bad, CFCs are the worst. Unfortunately, the picture is more complex. When occurring in the troposphere (the lower portion of the atmosphere – roughly below the 10-mile mark), ozone is a pollutant. When nitrous oxides and other fossil fuel gases are released from cars, trucks, and power plants, they interact with sunlight and form low-level ozone, an important component of smog. This pollutant is found in high concentrations where vehicle traffic is heavy, and it can cause widespread respiratory problems, worsening asthma and facilitating respiratory tract infections. Ozone in agricultural areas reduces vegetation growth and affects yields. Finally, low-level ozone acts as a powerful greenhouse gas, albeit much shorter lived than carbon dioxide.
Fact #3: Close to the surface of the Earth, ozone is a pollutant and a greenhouse gas.
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