06 November 2012

The Real Lessons of Ozone Depletion

Over at ChinaDialogue I have an essay up on the real lessons of the successful response to ozone depletion, motivated by the 25th anniversary of the Montreal Protocol. Here is how I start:
Twenty five years ago, the Montreal Protocol on Substances that Deplete the Ozone Layer was introduced for signature by nations around the world. Since that time, the treaty has become arguably the most successful international environmental success story in history. It may also be the one which historians and policy analysts have argued about the most in an effort to draw lessons relevant to the climate debate.

Conventional wisdom holds that action on ozone depletion followed the following sequence: science was made certain, then the public expressed a desire for action, an international protocol was negotiated and this political action led to the invention of technological substitutes for chlorofluorocarbons.

Actually, each chain in this sequence is not well supported by the historical record.
I argue that public opinion was not an important factor driving action, the presence of scientific uncertainty (and those touting it) was not an obstacle for action and the invention of technological substitues for chlorofluorocarbons helped reconfigure ozone politics to enable effective action. In this instance the role of governments was essential, but it was not what you might think -- I quote Karen Litfin:
“The issue resembles a chicken-and-egg situation: without regulation there could be no substitutes but, at least in the minds of many, without the promise of substitutes there could be no regulation.”
As will be the case with efforts to decarbonize the global economy, technological substitutes for carbon intensive energy generation will pave the way for international action. The question is, how do we accelerate technological innovation? If your answer is "targets and timetables for emissions reductions negotiated via a binding international treaty" then I'd suggest that you revisit the lessons of the ozone experience where innovation preceded a treaty.

ChinaDialogue has a companion piece from NRDC's David Doninger, which is largely compatible with my own essay, though he starts his story in 1986 when substitutes were already available.

Comments welcomed!


  1. Mr. Pielke,

    My name is Scott Sabol. I'm a meteorologist (SLU 1996) at WJW FOX8 in Cleveland.

    Over the years, I've continued to read as much as possible on the dynamics of climate science on many different sites trying to fill in the gaps on my understanding of climate change on both sides of the argument.

    Recently, I interviewed a climate scientist (pro AGW, over a few months time) and asked this individual a series of objectively stated questions which I just posted on my blog.

    I would love your input on these questions so that I can post the other side of the argument.
    Your input would certainly help my understanding of climate science.


    Thank you so much,

    Scott Sabol


  2. "Ozone depletion" was not and is not about CFCs. There's a reason the "ozone hole" still exists and still appears during certain times of the year only. It's about the physics and chemistry in Antarctica. CFCs were demonized for contributing to ozone depletion. The reality is that CFCs play an extraordinarily minor role in ozone destruction.

    The analogy is similar for "global warming". The best available science shows that CO2 plays at most, a very minor role in influencing global temperatures.

    The Montreal Protocol was a political exercise that achieved a great deal for DuPont (makers of "compliant" CFCs), but did nothing positive for humanity. The result of the Montreal Protocol was to make air conditioning and refrigeration more expensive, efforts that to this day continue to negatively impact people.

    The lessons of the Montreal Protocol are important... it would be foolish and ridiculous in the extreme to follow that same path with CO2.


  3. I agree 100%. Here is one example of innovation that will greatly help.

    Game changer: The "green" nuclear. Molten salt thorium nuclear reactors. Much cheaper, safer, and cleaner.

    Feb 2011

    "China has officially announced it will launch a program to develop a thorium-fueled molten-salt nuclear reactor, taking a crucial step towards shifting to nuclear power as a primary energy source."

    "The project was unveiled at the annual Chinese Academy of Sciences conference in Shanghai last week, and reported in the Wen Hui Bao newspaper (Google English translation here)."

    "If the reactor works as planned, China may fulfill a long-delayed dream of clean nuclear energy. The United States could conceivably become dependent on China for next-generation nuclear technology. At the least, the United States could fall dramatically behind in developing green energy."


    June 2012

    "The U.S. Department of Energy is quietly collaborating with China on an alternative nuclear power design known as a molten salt reactor that could run on thorium fuel rather than on more hazardous uranium, SmartPlanet understands."

    "Proponents of thorium MSRs, also known as liquid thorium reactors or sometimes as liquid fluoride thorium reactors (LFTRs), say the devices beat conventional solid fuel uranium reactors in all aspects including safety, efficiency, waste and peaceful implications."


    The solution is there. Technology developed in the US in the 60's. Just needs to be updated. Fortunately the Chinese (who do and will burn the most coal) are on to it. We can all breath easier.

  4. Roger
    as you know I have written a book about this which is partly visible on Google books
    You are certainly right that the search for CFC alternatives was on from the late 1970s and they were quickly identified. You are also right that there was no scientific consensus when the parties met in Montreal 1987 to sign the historic protocol. What you don't mention and what in my analysis shows is that the occurrence of the ozone hole changed the nature of the debate fundamentally. This phenomenon was a complete surprise to the scientific community and they communicate their shock effectively to policy makers.

    What we see in climate policy is an attempt to emulate the shock therapy without having the data. Massive ozone losses over Antarctica were real and unexplained for some time after the Montreal Protocol.

  5. The big scare over ozone depletion was an increase in UV radiation and thus more skin cancer. The problem with this scare is that the ozone hole occurs in winter, when the sun is standing so low above the horizon that all ozone depletion is counteracted by the long path through atmospheric water vapour.

    Any increase in skin cancer in the 70's can be fully atrributed to the increase of jet holidays to lower latitudes in summer an ski holidays to higher altitudes in winter.

  6. -3-Reiner Grundmann

    Thanks, and thanks for the link ... the ozone hole was far more relevant to what followed Montreal, and I would argue added momentum to a train that had already left the station.


  7. The differences between ozone and climate change are bigger than the similarities. I was around back then. No one lost a minute of air conditioning or refrigerator time. There was no punitive tax proposed on freon. No one proposed shutting down freon-using industries. From the public, there was a collective shrug of the shoulders, because we didn't seem to have any skin in the game. So whether freon did or did not cause the ozone hole really didn't matter to most folks.

    Climate change? Not so much. Just the disestablishing of the modern industrial state.

  8. @Reiner Grundmann,

    You said: "Massive ozone losses over Antarctica were real and unexplained for some time after the Montreal Protocol."

    While I am well aware that scientists were surprised to find the ozone hole over Antarctica, can you point to any positive evidence that it is in fact a new phenomenon and not something that has always been there without our being aware of it. With out such evidence your statement above would be unwarented.

  9. The big scare over ozone depletion was an increase in UV radiation and thus more skin cancer. The problem with this scare is that the ozone hole occurs in winter, when the sun is standing so low above the horizon that all ozone depletion is counteracted by the long path through atmospheric water vapour.

    Any increase in skin cancer in the 70's can be fully atrributed to the increase of jet holidays to lower latitudes in summer an ski holidays to higher altitudes in winter.

  10. Mark B -

    ===]]] From the public, there was a collective shrug of the shoulders, because we didn't seem to have any skin in the game. So whether freon did or did not cause the ozone hole really didn't matter to most folks. [[[===

    Just curious. Since you were around, are you aware of how many claims there were, such as in editorials in places like the WSJ, about how economic costly it was going to be to address the ozone hole? Did you read all the articles about how the concerns about the ozone hole were junk science?

  11. @ Matt:

    From the first International Geophysical Year (IGY) in 1957 onwards regular observatons of ozone (total column, vertical distribution) have been made around Antarctica. From the late 1970's satellites have been providing a more complete picture ( recently some older satellite "rudimentary" satellite measurements have been re-assessed, adding some information for the early 1970's).

    From all observational evidence we have no indication that the ozone hole was around before approximately 1980. I believe there has been one observation-based suggestion that maybe there was already ozone depletion as early as the late 1950's (if I remember correctly), but that has been investigated and caused by a faulty observations.

    There are plenty of official and personal webpages describing the physics and chemistry of the ozone hole as well as its history.

    About the history:


    Some "official" sites with past and current conditions:



    A nice "personal" site:


  12. Several years ago I took part in a workshop on the success of the Montreal Protocol.

    The conclusion back then was similar to what Roger describes here: compared to climate change the ozone problem was a "tame" problem: relatively few players, small economical impact, alternatives for what caused the problems (technological fix, if you want to), and an incentive for industry to take part (new business).

    The big warning from political scientists was not to use the ozone policy as a template for climate policy, as it most likely would not work.

    By the way, the development of new/alternative cooling agents has continued. The first alternatives simply had shorter atmospheric residence times so that they would not end up in the stratosphere. However, these are still strong greenhouse gases and remain long enough in the atmosphere (~ year) to have an effect. The latest generations of cooling agents with exotic names like "HFO-1234yf" have even shorter residence times (~ days-weeks) so that also their warming impact becomes negligible.

  13. Matt
    Two relevant papers were
    Farman, JC et al 1985. Nature 315
    Stolarski, RS et al 1986. Nature 322

    Joshua is right, there was a lot of industry resistance and science was used to oppose regulations for a long time. The Clean Air Act in the US (1977) controlled CFC in aerosol spray cans without empirical evidence (no measurements of decreased ozone, no increase in UV-B or skin cancer, etc). Industry thought this was setting a bad example. At the same time this was a tiny economic problem compared to climate.

    Somehow the link to my book got mixed up, it should be here

  14. @Jos

    "From all observational evidence we have no indication that the ozone hole was around before approximately 1980"

    This does not answer the question I asked. The question was is there specific positive evicence that the ozone hole did not exist prior to its discovery? A lack of evidence of prior existence is not an answer to this question. I tried a couple of your links and they do not provide an answer to my specific question.

  15. RE: Matt and Jos

    In other words, an absence of evidence is not evidence of absence.

  16. @ Matt, Bob.

    I don't how much more one can do than look at the available observations prior to roughly 1985 (there are plenty, dating back to the late 1950's), and look for "ozone holes". There are none, which fits with the current understanding of the ozone hole (which is one of the research topics I am involved in). And as far as I am concerned the basic understanding of ozone hole chemistry is quite far ahead of our understanding of climate.

    Priori to the late 1950's we have little to no information about Antarctic ozone, so in that sense I cannot prove nor disprove the prior existence of an ozone hole.

    So, where does that lead us? Given our current understanding and observational evidence, I think the question should be reversed: is there any reason to assume the ozone hole did exist before. From theory I do not directly see how that could have happened, at least not the current set of boundary conditions (i.e. ozone depleting substances).

    And without any hypotheses or observational indications of previous ozone holes I don't see the relevance of the question.

    But hat doesn't stop me from thinking about it from a much longer climate perspective (and other scientists do as well). Different climates with less/more oxygen and more greenhouse gases may have led to quite a different chemical composition of the ozone layer millions of years ago, and thus to quite a different ozone layer. But that is on another timescale, not expected to have happened in human history.

  17. ps. some people do try to look for ozone layer proxies in an attempt to look further back in time. Although not much is currently available, there is some hope that we'll find something.

  18. Roger,
    Great post, but I would add that it's not just been historians and policy analysts that have drawn the parallels between ozone and climate change. In 1985 Mostafa Tolba was actively pursuing the same sorts of mechanisms to combat climate change as those on ozone.

    The 1985 Villach Conference "on the Assessment of CO2 and other GHGs" recommended WMO, UNEP & ICSU set up the (small technocratic) Advisory Group on Greenhouse Gases (AGGG) -v similar to the Coordinating Committee on the Ozone Layer (CCOL)- in order to initiate if necessary negotiations on a global convention.

    The ozone 'success story' has very much been a part of IOs tactics for coordinating international action on climate change. An idealized vision of how scientific knowledge influences policy (along the lines of ozone) inspired the early science-policy entrepreneurs (namely Tolba).

  19. Jos,

    From what I see in your prior links, before satelite measurements starting around 1980 only surface measurments are available. It is my understanding that the satelights are primarily measuring stratospheric ozone. Am I wrong and they are measuing the full air column?

    How do surface instraments give us any information on the stratospheric ozone layer?

    Another piece of the CFC ozone depletion argument I have never seen a good expanation for is since CFCs are heavyer then air, how do / can manmade CFCs reach the ozone layer?

  20. Goodmorning to y'all (time difference Europe-US means I contribute once a day).

    @ Matt

    There are two different types of ozone measurements from satellites: total columns (full air columns), and vertical profiles. It has been common practice for scientists look at total air columns over Antarctic because nearly all variability is related to stratospheric ozone. However, there are also rudimentary profiles from instruments called SBUV, and that record also stretches back to the late 1970's. I mention "rudimentary" because for reasons that cannot quickly be explained the vertical resolution of such profile measurements is limited (typically one piece of information per 5-10 km vertically). Note that from halfway the 1990's onwards there are other types of satellite measurements providing better vertical information. And FWIW, the quality of the historical satellite profile measurements used to be less compared to the total columns, but it looks like the historical profile measurements have started to catch up.

    Before the satellite era there have been two other ways of measuring stratospheric ozone. One is by upward looking ground-based spectrometers, which in essence are doing the same thing that satellites do, but then from the ground. What that gives you is a total ozone column, but given that tropospheric ozone concentrations over the Arctic are small - as is its variability - one can safely assume that very nearly all variation in total ozone is related to stratospheric ozone. By the way, this is still being done today and extremely useful for validation of satellite measurements.

    The second method people use are ozone measurements from weather balloons. Equiped with a small ozone sensor, these weather balloons then provide vertical ozone information up to approximately 30-35 km altitude. This covers not the entire stratosphere and ozone layer, but it does cover the layers where ozone depletion occurs (15-25 km). Such balloons are also still operational at many locations around the globe, and again, extremely useful.

    Just about everything that has been measured by ground stations and balloons is freely available to anyone who is interested (including plots):


    Feel free to roam around and have a look at plots and data.

    As for the heavy molecules, there are different processes at work. One is gravity, but the other is mixing (either turbulence or diffusion (temperature)). The speeds at which molecules travel in thermal motion are so high that a bubble of heavy gas (relatively) soon diffuses freely into the atmosphere, especially with the assistance of wind and other disturbances. Of course, the short term effects can be more dramatic. For example, a lake of cool CO2 emerging from lake Nyos (Nigeria, if I am correct) was able to flow down a valley, killing all at low levels, but sparing things on higher ground. Within hours at most however, there were no pools of CO2 anywhere; it has all dispersed, heavy or not.

    Measurements of a heavy molecule like CF4 (which is extremely stable and remains in the atmosphere for likely more than 1000 years) show that it is very close to uniformly mixed in the stratosphere, despite being much heavier than "air" (oxygen and nitrogen), showing that mixing dominates gravity in the stratosphere.

  21. Jos:

    Thanks for the detailed info.

    I am at heart a skeptic about precision and claims of significance in science. One hears all the time about "surprising" findings from new and better methods that directly challenge previous work.

    I acknowledge straight-away that you make no outsize claims of "the science is settled." Far from it. Yet I am more cautious, and find it difficult to imagine a process that changes a *no* ozone hole condition to a large ozone hole condition in just a couple of years. It seems more likely to me that the technology and methods supporting these earlier ground-based measurements were, like many early efforts at anything, not sufficiently developed to capture an accurate picture. A "good start," to be sure, but still only a start.

    No data. Just an opinion.


  22. @ Bob91827

    Although it may appear the the occurence of the ozone hole was "sudden", it actually wasn't that sudden. We went from hardly any ozone depletion around 1980 to "current" levels around 1995. That's about fifteen years.

    In addition, ozone depletion is a non-linear process depending on many factors. For example, we recently showed that the amount of ozone depletion is very sensitivity to stratospheric temperatures. Ozone depletion depends on the formation of microscopical stratospheric cloud particles. And the formation of such clouds is highly non-linear: one degree lower or higher means clouds or no clouds. In the stratosphere, a seasonal temperature only a few degrees higher can lead drastically reduced ozone depletion because temperatures remain close to the stratospheric cloud formation temperature.

    This year was a "warm" year, and as a result we had the second smallest Antarctic ozone hole in 20 years an up to about 50% less ozone depletion. Only because of slighly warmer stratosphere of a few Kelvin.

    The non-linearity of ozone depletion (for example, ozone depletion roughly goes with the square of chlorine), fast increase in stratospheric chlorine loading (factor 3-4 between 1970 and 2000) and influence of other processes on ozone provide a good consistent explanation for the increased stratospheric ozone depletion between 1980 and 1995.

    And keep in mind that the Antarcic "ozone" hole is a rather unusual phenomenon that exists due to very specific meteorological conditions (isolated air masses within the Antarctic vortex) where all ozone can get destroyed, whereas ozone depletion outside of Antarctic has been very modest (~ 5% at max).

    Finally, although it is predicted that within about 50 years the "ozone hole" should be gone again (based on our current understanding), it is still a prediction that needs to be verified. Although there are indications that this recovery is starting, most colleagues agree it will take probably about 10 more years before we will be sure about the recovery (so please come back in 2020 ...).


  23. Cass Sunstein has a comment in the NYT, claiming that Montreal was made possible because President Reagan was a fan of const-benefit analysis and the calculations indicated it made good sense to sign the treaty.

    Sounds like the perfect antecedent for sensible climate policy (Stern style), doesn't it? Only problem, it doesn't fit the facts. I know of no history of ozone politics which could lend credibility to this claim. Anyone?