The Ozone Hole Remains

by Bill Chameides | November 10th, 2008
posted by Erica Rowell (Editor)

Permalink | 7 comments

A recent news flash from the European Space Agency: 2008 Ozone Hole Ranks Fifth Largest (see CNN and Science Daily coverage). Yes, after all these years, we are still worrying about the ozone hole.

Because there’s some confusion surrounding the ozone hole — some even mix it up with global warming — let’s start with a short primer.

Ozone is a molecule made up of three oxygen atoms. On the ground, ozone is a bad thing — it’s a major component of smog. But that’s not what the ozone hole has to do with. More than 90 percent of the Earth’s ozone exists in the upper atmosphere, or stratosphere, where it protects the Earth’s surface from damaging ultraviolet light (read more on ozone). This is a good thing — it helps guard against things like sunburn, cataracts, and skin cancer.

The Ozone Hole Explained

Discovered in the 1980s, the ozone hole is a seasonal phenomenon. During springtime in the Southern Hemisphere, the stratosphere’s layer of ozone over the Antarctic almost entirely disappears. (For more information see this NASA video.)

This hole is an extreme example of a more modest but still worrisome decline in ozone throughout the stratosphere caused by cold temperatures combining with halogens like chlorine, fluorine, and bromine. These halogens get into the stratosphere in large part through the breakdown of synthetic compounds used as refrigerants, solvents, propellants and foaming agents (think those pesky packaging peanuts), including chlorofluorocarbons (CFCs), hydrofluorochlorocarbons (HCFCs), and halons. (See full glossary.)

Ozone Hole History

While the ozone layer has been monitored since the late 1950s, it wasn’t until 1976 that a group of British scientists unknowingly recorded the presence of a major thinning in the ozone layer above the Antarctic. Initially believing their equipment was malfunctioning, they next assumed they were recording natural variations in ozone levels, perhaps due to changing volcanic or sunspot activity (sound familiar?). It wasn’t until 1983 when a record low clearly established a downward trend that they realized something big was happening to the ozone layer. It took another two years to fit the puzzle pieces together and conclude that those halogenated compounds were the culprit.

The Global Community Takes Action

The ozone hole discovery sounded an alarm. In addition to increasing the probability of sunburn and skin cancer, a thinner ozone layer means potential disruptions to ecosystems with flora and fauna sensitive to ultraviolet light (for more dangers from ozone depletion see here and here).

Amazingly, the global community took action. Starting with the Montreal Protocol in 1987, countries agreed to phase out the more potent halogenated compounds. As a result, the concentrations of ozone-depleting compounds have been declining (see here and here [pdf]). But the stratospheric response is much slower — once those halogens get up there, they stay for a long time. And so, the ozone hole persists, with this year seeing the fifth largest, in spite of the phase-out of the culprit compounds. In fact, scientists estimate that that the ozone hole will persist until sometime around 2070.

Are There Any Connections to Global Warming?

I mentioned earlier that people sometimes confuse the ozone hole with climate change. They are not the same thing, but it turns out there is a connection. The ozone hole requires cold temperatures. A little known fact about the greenhouse effect is that while increased greenhouse gases cause warmer temperatures in the lower atmosphere, they cause upper temperatures to cool. Hence, global warming has a tendency to exacerbate the ozone hole. As a result, the recovery of the ozone layer is being slowed somewhat by our greenhouse gas pollution.

In addition, the world’s response to the ozone hole carries an important lesson. By reaching consensus on an environmental problem, the global community was able to take concerted action to address it. Could the world community do the same for global warming?

The ozone hole experience is a cautionary tale about the dangers of delaying action on environmental problems. The first warnings about CFCs and the ozone layer were raised in the early 1970s by R. Sherwood Rowland and Mario Molina (who received the Nobel Prize for their work). If the world had acted then, there would probably be no ozone hole today. But thanks to the two-decade delay in phasing out the bulk of these compounds, we will have the ozone hole for many decades to come.

Global warming has an even longer reach into the future. Some of the carbon dioxide (CO2) emitted by the first Model Ts is still in the atmosphere causing global warming today. The CO2 we emit today will be warming the atmosphere 100 years from now. How much longer can we afford to wait?

SIDEBAR: What If ….
Here’s a fascinating historical tidbit. Thomas Midgley, the chemical engineer who invented CFCs, was also behind the idea of adding lead to gasoline. Both turned out to be environmental disasters. Midgley (1889-1944) was clearly a clever, innovative engineer but not very lucky when it comes to the environment. For me his legacy is an apt illustration of why all educational programs should include environmental sciences. Would Midgley and his company have advanced the use of these compounds had they appreciated their environmental impacts? Doubt it.

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  1. Ken Towe
    Dec 5, 2008

    “A recent news flash from the European Space Agency: 2008 Ozone Hole Ranks Fifth Largest” Every year in the fall the news media focus on the size of the Ozone Hole. This focus is misleading to the general public concerned with CFCs and ozone depletion because the SIZE of the ozone hole (its areal extent) is the result of a climatically controlled polar vortex that has nothing to do with CFCs. Seasonal stratospheric ozone loss is entirely restricted within the polar vortex which is a wind-driven feature. While the ozone trapped within this vortex may be temporarily depleted as a result of esoteric halide interactions on polar stratospheric cloud particles (also climatically controlled) the fact that the hole size has grown larger or smaller is independent of this chemistry. Obviously, if the polar vortex grows in size the area within it available for ozone loss increases, irrespective of the CFC burden. The polar vortex has been a seasonal feature at least since the mid-50s. It is commonly overlooked (ignored?) that in 1958 ozone losses were also encountered in the polar vortex, long before CFCs provided a significant addition to the natural stratospheric chlorine burden.” title=”Ozone hole size

    • erica
      Dec 5, 2008

      From DR. CHAMEIDES – Ken – Thanks for the clarification. Was not my intention to imply otherwise. ” title=”Thx

      • Ken Towe
        Dec 10, 2008

        “The ozone hole requires cold temperatures”….. Groking right along…. Perhaps there is more to the stratospheric ozone story than meets the eye? The “simple” stratospheric gas-phase chemistry of Molina and Rowland could not explain the ozone hole. A nitrate-limited, chlorine-based heterogeneous chemistry was substituted instead. According to this bizarre theory, the seasonal loss of Antarctic ozone within the polar vortex cannot take place until after threshold temperatures (–78 °C or below) are achieved (and maintained) allowing the formation of nitric acid trihydrate-seeded ice crystals in polar stratospheric clouds. NASA scientists say: “The maximum area of the hole is currently limited by factors such as the area of the cold air pool within the polar vortex, rather than by the availability of chlorine in the stratosphere’ (Geophys. Res. Letters, vol 19, p 1215).” Presumably, this is why no “hole” has developed in the Arctic vortex despite the presence of CFCs there; it rarely gets cold enough for long enough. But, the Antarctic has been cold enough, at least during the IGY studies in 1957-58 when interior temperatures below –80 °C were recorded at 50 mb (Ropar and Gray, 1961, Fig. 17). Ozone losses, obviously independent of CFCs in 1958, were detected (Goerler/Gray, 2000, p 28-32 Clearly, it must be very cold in the stratosphere, but what is unclear is why inorganic chlorine, specifically Cl from CFCs, is the control for this transient ozone depletion. A skeptic might point out that when the size of the Antarctic polar vortex got smaller, as it did in 1986, the October mean ozone level at Halley Bay went back up to its late-70s value. A reversal was also seen in 1988. This, in spite of the required cold air and the increased burden of CFCs. Is chlorine really necessary for polar ozone losses? And, does it have to be from man-made halogens? What about the concomitant increase of N2O…primarily a microbiological product but necessary for reactive nitrogen (NO, NO2) and nitric acid formation? More grok? “The first warnings about CFCs and the ozone layer were raised in the early 1970s by R. Sherwood Rowland and Mario Molina (who received the Nobel Prize for their work). If the world had acted then, there would probably be no ozone hole today.” Regarding the prize-winning Molina/Rowland warnings, it is ironic that their famous 1974 NATURE paper coincided with, and overshadowed, a paper in SCIENCE by London and Kelley ( confirming an upward trend (of unknown cause) in global total atmospheric ozone in the 1960s. The well-publicized downward trend in global ozone was not seen until after 1979. What really happened? The steady six-year depletion of ozone from 1979 to 1985, panicky at the time, had simply brought the mean global ozone level back down to near 300 Dobson units — the average total value London and Kelley gave for the late 60s. And then, from 1985 through 1990, and in spite of a 25% increase in cumulative CFC-chlorine into the atmosphere, global ozone remained virtually steady (Herman et al. J. Geophys. Res. 1991, Table 2). The six-year average was 301 ±2 DU. No net global ozone depletion since the 1960s, and none at all for six years running in the 80s? All very strange if CFCs are the cause and a global ozone depletion the effect. Do other data support the theory? In 1974 Molina and Rowland hypothesized that maximal ozone depletion from CFC destruction would take place in the middle stratosphere between 25 and 35 km, with negligible photodissociation of CFCs taking place below 25 km. Subsequent “where we live” studies, however, have shown that any large decreases in ozone take place in the lower stratosphere below 25 km. Furthermore, the catalytic ozone-destructive ClO molecules peak near 40 km with little or none present below 25 km. The inorganic chlorine below 25 km is HCl and CLONO2 and is derived predominantly from non-CFCs…organic compounds that contain no fluorine (Zander et al., 1992). Nothing much in the data fits the theory very well. Perhaps if Rowland, Molina and others had not ignored the research on the upward trend in total ozone in the 60s (they were completely aware of this in 1975), and had not chosen to start their curves in late 1978 with the first TOMS measurements from the Nimbus 7 satellite, the worrisome six-year downward trend might not have seemed so ominous and urgent to the public. Maybe CFCs would be less of an ozone depletion concern and more important as a greenhouse gas concern? The right result for the wrong reason?” title=”More Grok on Ozone?

  2. Kevin Moore
    Nov 19, 2008

    It is difficult to digest this statement: >>Global warming has an even longer reach into the future. Some of the carbon dioxide (CO2) emitted by the first Model Ts is still in the atmosphere causing global warming today. The CO2 we emit today will be warming the atmosphere 100 years from now. How much longer can we afford to wait? This is kind of like arguing that the water that Jesus drank is still on the earth. The cycle for Carbon is tremendous. The amount of CO2 produced and consumed each year is tremendous. Should we argue that some of the CO2 that Abraham Lincoln breathed is still on the Earth. Statements like this are an insult to the intelligence of the Duke Community. Let’s get to the real arguments. The debate should be strong about the effect (if any) of making sweeping changes in relation to Carbon. The cost would be exhorbitant. In addition, you can make strong arguments that you are just going to run manufacturing into 3rd world countries which will have even less stringent emission restrictions than they currently are under. Probably the largest immediate change that can be done is a major shift to nuclear energy for power. The technology for nuclear is better than ever. On global warming, we are now clearly in a 2 year cooling trend (some argue it began 7 years ago). I know that the hard core CO2 arguers don’t want any mention of a counter argument, but the numbers are valid. They should be debated. On a site like Duke Research, there should be a real debate of these topics and not just sweeping statements. Global cooling models are coming up left and right now as we improve the models. They still have a long way to go.” title=”Global Warming Comments

    • erica
      Nov 20, 2008

      DR. BILL CHAMEIDES responds – Kevin, About the CO2: You’re actually wrong. CO2 from fossil fuels has a distinct carbon-isotope signature, different from that cycled by plants and humans. We can see that signature in the CO2 in the atmosphere today and we can see the change in that signature over time. So yes, the CO2 from the first Model Ts is still in the atmosphere. About the short-term cooling trend: I just finished doing a four-part series on that very subject in this blog and had a rather healthy debate (see…%5D/globalwarmingiceageseries). I guess you missed it. Perhaps your remarks about Duke are misplaced? About models: It is incorrect to argue that our understanding of the role of CO2 in climate change is based on models — actually its based on observations. Again, you need to check out my earlier posts.” title=”CO2 from Model Ts is actually still up there

      • Kevin Moore
        Nov 20, 2008

        >>How much longer can we afford to wait? This statement is based on models (obviously inferred). I’m a Chemist (Duke PhD, 1993) and not a Geologist, but I’ve always understood Carbon to have a much shorter life span than what you are inferring(Model T=100 years). I struggle with the dramatics of your relationships. For instance, saying that global warming is causing cooling in the upper atmosphere and thereby “exacerbating” the Ozone Hole. We are talking about less than 1 degree Celcius over 100 years on surface temps. So how much of this cooling is taking place in the upper atmosphere? Does Ozone’s concentration have such a wild fluctuation with temperature that it can really be affected as much as you are describing by such a small change in surface temps??? You are saying that the hole is worsening because of the warming. Is that 0.0001% worse or is it really statistically significant. This kind of correlation makes it look like the discussion has a political intent rather than a scientific intent. I have since read some of your other pieces which are definitely more informative than this was. I grow weary of the political bend of this discussion. My 4th grader last year had a day of discussing why CO2 is such a horrible *pollutant*(should we shoot the dog because she is polluting?). This after watching Al Gore’s movie and never being told that he was not a scientist. My 7th grader was told if he really cares about global warming, he should ride his bike to school rather than ride the bus (never mind that the bus is coming to that stop anyway every day regardless and that buses are actually one of our better conservation methods). These statements are made in science class. What an opportunity to teach about the scientific method and current efforts to investigate the causes of global warming and develop accurate models to predict its effects! But no, in science class they are spewing out ignorance. Even if 10% of America switched to bikes rather than cars today, the effect on global temp would be negligible for years to come. CO2 is being given too much credit as a greenhouse gas. I watch people at my workplace put all of this energy into plastic recycling even though it has been shown that it is a net energy loss to recycle it. Why would we do it if it is a net energy loss? One Biologist argued that it keeps the landfills clean, but studies have shown that plastic is less than 0.3% of landfills. It all comes from ignorance. Science is about seeking the truth. I’m concerned that our political agendas are tilting our interpretation and pursuit of scientific data.” title=”Global Warming…

        • erica
          Dec 5, 2008

          From DR. CHAMEIDES – Kevin – I am a scientist and my discussion of the science has nothing to do with politics. Should I impute your statements to politics and not your knowledge as a chemist? And while we are on the subject of your chemical background, I suggest that you use caution when weighing in on subjects that are obviously beyond your expertise. Just because you have a Ph.D. in chemistry does not mean you understand how chemicals behave in the atmosphere. The reason CO2 stays in the atmosphere so long is because its ultimate sink is dissolution in the deep ocean and this takes a rather long time. How do we know this? We have an isotopic signature for fossil fuels involving C-13. We can track that C-13 and we can confirm that it does indeed remain in the atmosphere for quite a long time. I assume as a chemist you know about isotopes and how they can be used as chemical signatures. And the cooling of the atmosphere from increases in greenhouse gases is a very straightforward outcome from considerations of radiative transfer. I had not heard before that the study of radiative transfer is political in nature. And because of the lower density of the upper atmosphere, the temperature change in the upper atmosphere is larger than that of the lower atmosphere. The later portion of your comments reflect a serious misunderstanding of my position and of much of my fellow environmental scientists. Using these arguments to discredit the scientific basis for action on environmental issues is halfway between an ad hominen attack and an ignoratio elenchi. You choose.” title=”It’s about science

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