• When asked to describe global warming, people often responded that it is a problem with a hole in the ozone layer.
• The public also thinks that there is a causal link between the ozone hole and the planet warming up.

This short summary explains the confusions experienced by the general public, offers suggestions for improving the public's understanding, and shows how scientists can help people adjust their mental frames about climate change.

Linking Mental Models

Misperception: "More of the sun's radiation (or heat) gets in through the ozone hole, and that's why it's warming up down here."

Many people interviewed for the Frameworks research connected what they understood about the "ozone hole" to help them understand global warming by simply using their mental model of ozone depletion as a starting point to grapple with the causes of climate change. This type of thinking—which may seem odd to experts who understand the ozone and climate change issues clearly—is a typical mechanism employed in all learning: we extend existing mental models to make sense of new information.

Misperception: "There are these heat-trapping gases that cause a hole in the ozone layer..."

The second type of confusion also inappropriately links two different mental models: the gases that destroy the ozone layer are the same as those that trap heat and cause global warming. That is, of course, partially true-chlorofluorocarbons (CFCs) and ozone itself are heat-trapping gases. But this understanding misses the primary heat-trapping gases—CO2, methane, and nitrous oxide—and therefore fails to identify the pervasive human activities underlying human-driven climate change. (Note: N2O both traps heat and reacts to form NO in the stratosphere, which leads to catalytic destruction of ozone in all but the lowest portions of the stratosphere. So, it, too, performs a dual role in both problems.)

Background

Global warming and ozone depletion are two separate but related environmental threats. Global warming and the greenhouse effect refer to the warming of the atmosphere (mostly in the lower part, also known as the troposphere) due to increasing concentrations of heat-trapping gases. By contrast, the ozone hole refers to the loss of ozone in a higher part of the atmosphere, known as the stratosphere. Ozone loss is a serious concern because stratospheric ozone blocks incoming ultraviolet radiation from the sun, some of which is harmful to plants, animals and humans.

Over the past few years, scientific inquiry has revealed a complex set of mutual interactions between these two problems, making it ever more understandable that the general public is confused about the two issues: (1) the upper-atmospheric ozone depletion contributes to shifts in climate patterns, (2) lower-atmospheric ozone formation contributes to the warming effect, and (3) the emission of certain gases and resulting climate changes lead to cooling of the stratosphere, i.e., precisely to the conditions that enhance the depletion of the ozone layer.

Because most people have no or little background in basic atmospheric science, however, it may be helpful, should questions about the ozone-climate change link arise, to precede more specific details with an overview of the layered structure of the atmosphere. This will help people understand that most of the gases that make up our atmosphere—including those that make up the heat-trapping "blanket"—are actually located in the lower-most portion of the atmosphere, the troposphere, while the ozone layer is within the layer above, the stratosphere (see graphic). Weather dynamics occur in the troposphere under the strong influence of Earth's surface and to a lesser extent under the influence of the dynamics in the stratosphere.

• Some human-made gases, called chlorofluorocarbons (or CFCs), trap heat and destroy the ozone layer. Currently, these gases are responsible for less than 10 percent of total atmospheric warming—far less than the contribution from the main heat-trapping gas, carbon dioxide. [Since the Montreal Protocol, which regulates the emission of ozone-depleting substances, the use of CFCs is being phased out.]
  
• Some of the gases used to replace ozone-destroying chemicals are highly potent, if shorter-lived heat-trapping gases—HCFCs, still affecting ozone and thus considered only a temporary replacement, and HFCs. These substances will remain in the atmosphere for years or, a few of them, for decades. Thus, they resolve one problem but add at least to some extent to another. [Note: Because HFCs are powerful heat-trapping substances, the Kyoto Protocol includes them in the "basket" of regulated gases.]
  
• Ozone itself is a heat-trapping gas, so it adds to warming wherever it is found, albeit the mechanisms differ. Near the ground, ozone is formed from air pollutants and traps heat. In the stratosphere, ozone heats the surrounding air when it is photo-dissociated by solar ultraviolet photons, but cools the surrounding air when it radiates infrared energy to space. The heating effect, which occurs only in daylight, is more effective than the cooling effect, which occurs day and night.
  
• As the higher atmospheric (stratospheric) ozone layer gets destroyed, there is less photo-dissociative warming, and hence a cooling of the stratosphere. [Note: increases in methane and water vapor add to the cooling of the stratosphere.] This offsets part of the overall warming effect produced by other heat-trapping gases in the rest of the atmosphere. The resulting lower overall warming may be misleading, however, as it does not imply no or only little climate change. Rather, the cooling of higher layers of the atmosphere can produce changes in weather (wind) patterns in the higher latitudes. Thus, the chemical changes in the different layers of the atmosphere lead to dynamic changes that can have global and regional consequences for the climate.
  
• The colder the stratosphere gets, the greater the destruction of the protective ozone layer, or, differently put, the slower the recovery of the ozone layer.

Reducing ozone-depleting gases is crucial to prevent further destruction of the ozone layer, but eliminating these gases alone will not solve the global warming problem. On the other hand, efforts to reduce all types of emissions to limit global warming will also be good for the recovery of the ozone layer.

And while you're at it...
...Clear up a related confusion: "good" and "bad" ozone

Confusion: Given the problem of ozone depletion, how come we get ozone alerts, meaning high levels of ozone?

You may want to help people distinguish between the two primary "ozone problems."

A simple way to distinguish between the two is to label them with qualifiers that connect to human health impacts. Stratospheric ("upper air") ozone is "good ozone" or "protective ozone" in that it shields us from ultraviolet radiation, which can cause eye and skin damage in humans, impact the immune system, damage crops and destroy phytoplankton in the oceans, the basis of the marine food web.

While ground-level ozone also protects us from the sun's ultraviolet radiation, this benefit is overwhelmed by its contribution to air pollution. Ground-level ozone is "bad ozone" or "destructive ozone" because as an air pollutant in the air we breathe, it contributes to smog and damages lung tissue, especially in the young, old, and in people with heart and lung problems. Bad ozone also causes damage to plants, crops, and plankton in the ocean, and reacts with other air pollutants that are damaging lung, eye and throat irritants.

Episodes of elevated ozone concentrations near the ground occur particularly on hot days. Thus the prospects of global warming suggest that the conditions for ozone alerts will be met more frequently, especially during the summer in urban and coastal areas, but even in rural areas. The fact that global warming will likely worsen existing air pollution and related health problems is yet another reason why many people confuse the two issues.

The Explaining Mechanism

Interestingly, Frameworks research also shows that the general public has a much better grasp of the mechanism of ozone depletion than of the causes of climate change. The "simplifying model" used to explain stratospheric ozone depletion—i.e., the hole in the ozone layerihelped explain that abstract scientific issue to the average person. As a result, many Americans understand the problem of a thinning ozone layer as being akin to a hole in Earth's roof, and were thus motivated to take political action to fix the hole. Frameworks claims that ozone depletion is an example of a complicated scientific issue that was framed well and suggest that a similar technique could work to improve the public's understanding of climate change and what it will take to solve the problem.

Further information:

Overview of ozone and the atmosphere (including the evolution of the atmosphere, ozone layer formation and destruction, and the structure of the atmosphere)
http://daac.gsfc.nasa.gov/

Connections between climate change and ozone depletion
http://www.ndsc.ncep.noaa.gov/climchng.html

Other misconceptions about climate change and ozone depletion:
http://www.gcrio.org/gwcc/misconceptions.html
(note, this is slightly dated; scientists now see a number of connections between the two models; see first link)

Climate change may become major cause of ozone loss
http://www.gsfc.nasa.gov/topstory/20020422greengas.html

The effect of climate change on ozone depletion
http://www.msc-smc.ec.gc.ca/education/arcticozone/change_e.cfm

Ozone recovery delayed by global warming
http://www.giss.nasa.gov/gpol/abstracts/1998/ShindellRindL.html

Kirk-Davidoff et al., 1999. "The effect of climate change on ozone depletion through changes in stratospheric water vapour." Nature, 402, 25 November, pp. 399-401.

This science primer was written by former UCS Staff Scientist Susanne Moser and reviewed by Dr. Mario Molina, Massachusetts Institute of Technology, and Dr. Charles Kolb, Aerodyne Research Inc. This document cannot be reprinted or reposted to electronic networks without permission and acknowledgement.