It’s official: we really have saved the ozone layer During our little climatic digression in this week’s podclast, Chris brought up a study that I hadn’t heard about, in which Paul Newman (no, not that one) of NASA’s Goddard Centre (who have a nice write-up) and his colleagues play a game of climatic what if: what if the discovery that chlorofluorocarbons (CFCs) destroyed stratospheric ozone had been ignored, and were not phased out in the decade following the signing of the Montreal Protocol in 1987? Do our more sophisticated climate models, which can more accurately simulate atmospheric chemistry and wind patterns, confirm the hypothesis that if we had continued to emit CFCs and other ozone destroying chemicals, the ozone layer would have been severely damaged?
To answer this question, Newman et al. ran two scenarios in the same climate model, and charted the evolution of stratospheric ozone in each. The first model was based on the current (low) emissions of ozone-destroying chemicals resulting from the implementation of the Montreal Protocol; in the second, rather poetically named “world avoided” model, CFC emissions increase by 3% a year (“business as usual”) after 1974, when the ozone alarm was first sounded (and was presumably ignored in this parallel universe).
Animations fully depicting the results of both scenarios between 1974 and 2065, are available, and are well worth a watch. Below I show some edited highlights: side-by-side comparisons of the two models during September/October (southern hemisphere spring, when the Antarctic ozone hole reaches it’s maximum extent) in 2008, 2020, 2040 and 2060.


The snapshot from last year already shows a clear divergence between the two models; the ozone hole in our reality is still prominent (once you account for the difference in scale, it matches quite well with the actual one), but far more ozone seems to be being destroyed in the world we avoided. The models therefore suggest that even though the ozone hole hasn’t fully healed, cutting back on CFC emissions has clearly limited the extent of the damage.



This difference in the south polar region becomes more pronounced through 2020 and 2040; the animations also show that by 2040, the Antarctic of the “world avoided” has an ozone hole for all or most of the year, rather than just for a couple of months. Even more ominously for the residents of this alternative world, the much bluer colours at lower latitudes indicate that ozone depletion is also occurring outside the polar regions. In fact, by 2040 the average atmospheric concentration of ozone is below the 220 Dobson Units (DU – see the scale below the 2008 figure) which is used to characterise the modern ozone hole. So in a certain sense, there is no ‘hole’ anymore – it’s gone global.


And if that looks scary, by 2060 there’s virtually no stratospheric ozone anywhere. It’s gone, and with it our protection against ultraviolet radiation. The authors put it in pretty stark terms:

DNA damaging UV for the [Northern Hemisphere] midlatitudes increases by approximately 550% between 1980 and 2065.


It should be noted that these models only looked in detail at the upper atmosphere, and did not model the interaction between the atmosphere and oceans; sea surface temperature data from runs of properly coupled climate models was used as a boundary condition instead. The effects of the excess CFCs, which are themselves potent greenhouse gases, on sea surface temperatures is therefore not included in the “world avoided” model; and the chemical effects of greater ultraviolet penetration into the lower atmosphere are also unconstrained. Despite these uncertainities, however, it seem pretty clear that we got our environmental act together just about in time to dodge a rather carcinogenic bullet.
P. A. Newman, L. D. Oman, A. R. Douglass, E. L. Fleming, S. M. Frith, M. M. Hurwitz, S. R. Kawa, H. Jackman, N. A. Krotkov, E. R. Nash, J. E. Nielsen, S. Pawson, R. S. Stolarski, & G. J. M. Velders (2009). What would have happened to the ozone layer if chlorofluorocarbons (CFCs) had not been regulated? Atmospheric Chemistry and Physics, 9, 2113-2128. (open access)

Categories: climate science, environment, paper reviews

Comments (44)

  1. Paper Hand says:

    Wow … that 2060 is FRIGHTENING.
    I do wonder how realistic it is to assume continuous increase in CFC’s, wouldn’t it have plateaued at some point?
    Still, very interesting article! That sixfold increase in UV by 2060 is astonishing. How much would that have increased the cancer rate?

  2. Brian X says:

    You know, I was a little young to be in the loop when the Montreal Protocol went through, but I would imagine that the only thing keeping chlorofluorocarbon-generated ozone deficiency denialists from being as strident as anthropogenic global warming denialists are now was lack of Internet access.

  3. Who Cares says:

    What is the average distance between historical data points?
    How can they justify extrapolation past this distance?
    I’m asking this as someone who worked on a program that converted (pseudo)point temperature measurements into a
    2D field, and got some really nifty results back (temperatures trying to go to +/- infinity) at the edges of the field if the extrapolation just continued.
    Bonus question for the deniers: Why would I need Co2 sensors when testing in a greenhouse (producing vegetables) so that I can compensate for the difference between average and real in the formulas used?

  4. BrianR says:

    Interesting study … out of my field of expertise to truly evaluate its merit, but I think these ‘what if’ modeling studies are important.

  5. I suspect that even if there had been much more heavy duty pro-CFC (for lack of a better term) lobbying that the CFC production would have still been cut well before 2060. I’d be more curious therefore what the model shows if a Montreal Protocol were implemented now or say in 2020. How bad would 2060 look then?

  6. Greg Laden says:

    Had Bush been president of the US during the previous eight years, how would this have turned out?

  7. JohnO says:

    Please forgive my ignorance on this subject but we all hear about the hole in the ozone layer which was discovered in the 1980s?
    What I wish to know is, how much work was done before this time to find out if this is not a natural occurrence.
    I know the solar particles are funnelled down at the poles by the Earth’s magnetic field so these would normally be weak spots. What I have NEVER seen is information on the ozone layer at the poles BEFORE this discovery. Is the information there for the general public to see? I wish to be educated NOT to follow blindly. Thank you.

  8. JohnO says:

    Sorry, missed a comma before NOT.

  9. Blas says:

    Have news for you, Greg: Bush was President in 1987. Now, let’s all remember these are pictures produced by a computer of things that never happened and, according to the article, never will. They show what might have happened if the assumptions programmed into the model were correct. But that’s something we’ll never know, so they belong in the science-fiction category.

  10. ScienceWoman says:

    One thing I’m curious about is the apparently high ozone concentrations over the southern ocean. It’s something I haven’t noticed in the observational data. Is it a modeling artifact? Or a real phenomenon? (Congrats on your front-page billing.)

  11. John Drake says:

    I have always been amazed by the connection of a gas that degrades in UV is really heavy(aka does not float) that some how .. probably by the power of jesus or allah or jehovah(we know how much they all hate us) makes it into the upper atmosphere to destroy our ozone … amazing

  12. Silver Fox says:

    Have news for you, Greg: Bush was President in 1987.

    Reagan was President 1981-1989 with G.H.W. Bush as VP; G.H.W. Bush was President 1989-1993 (election was November, 1988).

  13. Chris Rowan says:

    One thing I’m curious about is the apparently high ozone concentrations over the southern ocean. It’s something I haven’t noticed in the observational data. Is it a modeling artifact? Or a real phenomenon?
    I noticed that too – it kind of makes sense, because most ozone is produced in the tropics and migrates to higher latitude, and when the circumpolar winds are strong it will therefore pile up against it. You do see hints of the same thing in some of the maps (like the one on this page – it’s possible the model exaggerates it somehow.

  14. Todd Peterson says:

    Just propaganda to make us believe that natural variations in the Eatrh’s climate can be altered by tax-payers.

  15. Chris Rowan says:

    Please name a natural source of CFCs.

  16. BrianR says:

    Note to the anti-science punditry … might want to make sure you spell ‘Earth’ correctly to more effectively make your case.

  17. Alex says:

    I was wondering why there weren’t ozone deniers, and then one turned up in comments at Fistful of Euros. I do remember George H. W. Bush referring to Al Gore as “ozone man”, though; they’ve been the Stupid Party for a long, long time.

  18. JohnO says:

    Didn’t say that there was a natural source for CFCs. I only asked what research had been done in the previous 50 years or so to give information on the natural conditions of the ozone layer at the poles. Can you point me to a source of information which gives data for this time period?
    Thank you.

  19. Randall thompson says:

    It’s funny, but i just released that Dupont always seems to be behind all the big screw ups. Leaded gas, Freon, making hemp for rope illegal so they can sell nylon. Can you think of anything else?

  20. Robert P. says:

    John O.: measurements of total ozone over antarctica began in 1956, and were used as a reference by the British Antarctic Survey when they first reported the “ozone hole” in 1985. You can find a scan of their original figure at:
    Silver Fox: the Montreal Protocol was indeed negotiated by the Reagan Administration (specifically George Schultz’s State Department and Lee Thomas at EPA.) There was resistance from Donald Hodel et al. from Interior, but Reagan overruled it. Back then, atmospheric chemistry had not yet become a partisan issue.
    Robert P.

  21. Tally says:

    Please name a natural source of CFCs.
    Posted by: Chris Rowan | March 25, 2009 7:40 AM
    CFCs are fairly inert and don’t react with well anything. When CFCs break down one of the byproducts is just basic chlorine. It is the chlorine that destroys the ozone. I know this conflicts with your ideology and your not going to believe me, but chlorine is natural; it’s an element, it’s not man made.

  22. Chris Rowan says:

    The chemical stability of CFCs is the reason they can reach the stratosphere – where the ozone layer is – before they break down, unlike other, more reactive, chlorine and bromine compounds. Which is why we have a stratospheric ozone layer in the first place.

  23. KatharinavB says:

    How very interesting. It is always good to see old predictions evaluated.

  24. Kerry says:

    You should look at the actual reaction mechanism that Roland and Molina discovered (ozone degradation from CFC photolysis). They won the Nobel Prize in Chemistry in 1995 for discovering this reaction.
    If you need more evidence for manmade CFCs degrading ozone, we’ve found a bunch of fluorine in the ice and atmosphere in the South Pole. This HAS to be man made because there are only few natural sources of fluorine (volcanos, erosion of marine animal shells, etc.). These sources of fluorine would not make it to the stratosphere over the South Pole because they would quickly degrade. CFCs, as you and Chris Rowan mentions, are relatively inert, so the have a chance to make it up there in the first place.
    Yes, chlorine is naturally occurring, but it up to the stratosphere is a challenge. Chlorine is very reactive, so it’s not like it would wait until it drifted up into the ozone layer to react. The only reason chlorine has a chance to react with ozone is because it was transported there in the stable form of CFCs.

  25. ian says:

    Can you please post the results of Ozone depletion in 100 year increments going back to approx 5000 BCE? I need to know how our CFC changes compare to natural fluxuations in the Ozone layer to know if we are really effective, or simply assigning the assumed cause to the observed effect.

  26. BrianR says:

    ian says:
    “Can you please post the results of Ozone depletion in 100 year increments going back to approx 5000 BCE?”
    sounds like a good idea … how come you can’t research that yourself instead of demanding it from others?

  27. JohnO says:

    Thanks Robert P.
    I was hoping research had been started earlier but it will have to do.

  28. DouglasK says:

    Recently, the University of Waterloo released a study about the Ozone Layer v CFC’s v Cosmic Radiation … It would seem that Cosmic Radiation may be a major player here as well.
    It also has good data for about a 22 year period of measurement. Cheers!

  29. Chris Rowan says:

    Hmm, interesting. Although note that the mechanism proposed by the author still involves CFCs – it’s just that cosmic rays are breaking them up rather than solar radiation.

  30. Simon Sammut says:

    We all need to remember that this is all conjecture with science behind it. Our models are getting better but the world is ver complex. CFCs are not natural and do act as a vector to carry harmful chlorine where it previouslh had not gone before (this in itself is concerning had we kept producing it). Yes the ozone does deplete with cosmic rays, but the planet evolved with this and has done so for millions fo years before. CFCs are relatively new and adds new pressures to the atmosphere that were no there before. If we were to lose our ozone layer, the cancer rates would be the least of our worries, it would have a devestatin impact on or ecology that we depend on for… everything. The mass devestation of the UV frying everything would be too catastrophic to contemplate. Best course of action would be to avoid such a possibility even though we don’t hav ALL of the information… same with global warming.

  31. naturalist says:

    Ironic how obstructionists, denialists, Libertarians and Neocons who constantly complain about the lack of personal responsibility of liberals and others, always seem to stop short and protest loudly when it comes to being mature enough to accept personal responsibility for how some of our human endeavors have detrimental effects upon the ecology the planet. Basically,if it does not fit into their myopic ideology or delusional religious beliefs, then it isn’t real.

  32. Simon Sammut says:

    Fred, please keep the tone friendly, this is an intellectual discussion. My earlier comment acknowledged that cosmic and other solar radiation has diminshed ozone in the past and will continue to do so, but the planet has ‘evolved’ with this. CFCs may (or not) be contributing to the depletion of ozone (evidence may suggest that it does but cannot possibly ever be conclusive). The prudent move would be to move away from activity that may endanger us. How has finding alternatives to using CFCs hurt us really (unless you manufactured it)? It may have been a waste of time… but what if it wasn’t? I don’t believe it was a waste of time, and cannot draw any conclusive proof either way. If time is a factor, you cannot wait to get all of the evidense beyond reasonable doub can you? If someone told you a swarm of deadly angry wasps may (or not) go through the path you are on, but it was a lot less likely on another slightly longer path, surely you would move to the other path to be sure!

  33. Gordon Shumway says:

    Pushing thru the market square, so many mothers sighing
    News had just come over, we had five years left to cry in
    News guy wept and told us, earth was really dying
    Cried so much his face was wet, then I knew he was not lying
    I heard telephones, opera house, favourite melodies
    I saw boys, toys electric irons and t.v.s
    My brain hurt like a warehouse, it had no room to spare
    I had to cram so many things to store everything in there
    And all the fat, skinny people, and all the tall, short(like Simon) people
    And all the nobody people, and all the somebody people
    I never thought Id need so many people

  34. FrankleeMiDeer says:

    Does it seem as if the antis/deniers/righties are always meaner/angrier/nastier? Seems so to me.

  35. David Ahlport says:

    re: Fred
    Actually, as usual, Anthony Watts lies like crazy.
    As the blog author here mentioned above:
    “The mechanism proposed by the author still involves CFCs – it’s just that cosmic rays are breaking them up rather than solar radiation.”

  36. SimonG says:

    I don’t recall much by way of ozone-denialism at the time. I suspect that a strong reason for that was that ultimately, doing away with CFCs didn’t have a massive impact on anyone’s lifestyle: there are suitable alternatives for most applications.
    With climate change, tackling the problem will have a significant affect on all our lives. Short-sighted greed and laziness rule.

  37. Does it seem as if the antis/deniers/righties are always meaner/angrier/nastier? Seems so to me.

  38. KA Reed says:

    Thank you for posting this very interesting report.
    The thing that bothered me about the report is that either the report’s author or the two scientists seemed to demand an either/or result of the two tested energy sources (UV vs Cosmic Rays) for the reaction. As a Biologist, it seems unrealistic to me to expect the CFCs to differentiate between the two, if the weaker/more abundant UV Rays are able to supply enough of the right kind of energy to do the job, but the higher-energy Cosmic radiation particles would logically energize more reactions. And *that* is what the data seems to say to me: that *both* forms of radiation can provide sufficient energy for the endothermic chemical reactions that break down CFCs, releasing the chlorine that catalyses a chain-reaction destruction of ozone.
    While the UV-CFC reactions may only have sufficient energy to break down the CFCs, releasing the catalysing Chlorine that causes chain-reaction breakdown of O3; it seems likely to me (assuming I didn’t miss something) that not only could the higher energy Cosmic Rays break up CFCs, but also the Beta particles could conceivably breakdown ozone directly. I will have to read-up on this fascinating discovery some more!

  39. orangy68 says:

    Not quite sure what the point of this article is. And surely any hypotheses based on future events without taking countless other variables into account. Some of the comments made for interesting reading during todays insomnia. The illustrations are pretty too. Good job because they are all based on science fiction as yet!! Kindest regards. And keep seeking the truth. 100 proof. Do you think we are seriously antediluvian (my 5th use of this word today) Signed. Prince Charles. England.

  40. shiva says:

    Are CFC’s only things that cause destruction of ozone layer?

  41. lylebot says:

    DNA damaging UV for the [Northern Hemisphere] midlatitudes increases by approximately 550% between 1980 and 2065.

    In other words, we all could’ve had mutant superpowers. Thanks a lot, scientists.

  42. yogi-one says:

    I think it was a good example of scientists getting the message out, and the people pushing the markets to provide then with alternatives to CFCs, in the last decade that it was possible to do that, the 1980s.
    CFCs were a good cause, probably because, as noted, neither the fossil fuel industry nor the big pharma was much affected by it. Everyone could jump on the bandwagon against CFCs and come out looking good. So they did.
    Not so with fossil fuels. And that’s going to push a mass extinction event which we will survive, but expect more Haiti’s and 2004-like tsunamis, and Katrina-like huriicanes before we get there. Oh yeah, and good bye Maldives!
    We’ll come out of it poorer, in a curious dark-age of hi-tech (those who can afford technologies will have them, most won’t) in a world with some fraction of the biodiversity we enetered the 20th century with (maybe 1/3 as many species), in a world altered by changing weather patterns, featuring habitats changed by shifting climate patterns and overrun by non-native flora and fauna.
    If it was such a good deal for everyone to switch off fossil fuels we could have fared much better.
    In the case of fossil fuels, the ‘world avoided’ scenario is much better, because we chose, if not the ‘do-nothing’ scenario, the ‘do-not-much’ scenario.

  43. sharon says:

    Wonder how the world would look if the internal combustion engine had never been invented? Ecologically, politically, etc.