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CFCs contribute only a fraction of global warming

What the science says...

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CFCs contribute to global warming at a small level.

Climate Myth...

It's CFCs

"The observed data show that CFCs conspiring with cosmic rays most likely caused both the Antarctic ozone hole and global warming... The total amount of CFCs, ozone-depleting molecules that are well-known greenhouse gases, has decreased around 2000. Correspondingly, the global surface temperature has also dropped." (Qing-Bin Lu)

A paper published in an obscure physics journal by the University of Waterloo's Qing-Bin Lu (2013) has drawn quite a bit of media attention for blaming global warming not on carbon dioxide, but rather on chlorofluorocarbons (CFCs, which are also greenhouse gases).  However, there are numerous fundamental flaws in the paper, which is based almost entirely on correlation (not causation) and curve fitting exercises.

Lu's hypothesis was disproven very simply by Nuccitelli et al. (2014).  Lu argues that the radiative forcing (global energy imbalance) from CFCs matches global surface temperatures better than that from CO2 over the past decade.  This is because as a result of the Montreal Protocol, CFC emissions (and emissions of hydrofluorocarbons, which replaced CFCs) have been flat over the past decade, and global surface air temperatures have also been essentially flat during that short timeframe, while CO2 emissions have continued to rise.

However, a global energy imbalance doesn't just impact surface temperatures.  In fact, only about 2% of global warming is used in heating the atmosphere, while about 90% heats the oceans.  Over the past decade, ocean and overall global heating have continued to rise rapidly, accumulating the equivalent of about 4 Hiroshima atomic bomb detonations per second (Figure 1).

Fig 1

Figure 1: Land, atmosphere, and ice heating (red), 0-700 meter OHC increase (light blue), 700-2,000 meter OHC increase (dark blue).  From Nuccitelli et al. (2012).

So while CFCs might match surface temperature changes better than CO2 emissions over the past decade, CO2 emissions better match the relevant metric – overall global heat accumulation.  Since a global energy imbalance influences global heat content and not just surface temperatures, this by itself is sufficient to falsify Lu's hypothesis (though the paper contains several other fundamental problems – see the Advanced level rebuttal for details).

Last updated on 14 April 2014 by dana1981. View Archives

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Comments 26 to 34 out of 34:

  1. Could ozone depleting chemicals and the other GHGs (with a large revision downward of CO2 radiative forcing and amplification feedbacks?) explain a modestly warming upper troposphere, higher tropopause, and a cooling stratosphere that are among the markers of anthropogenic climate change? Wouldn’t that also align with the strong empirical evidence of very little global warming since the preindustrial era until 1950 that then really accelerated after the 1950s and 1960s as CFCs, HFCs, halons, and SF6 emissions skyrocketed from their industrial use as refrigerants, solvents, propellants, and electrical insulating gasses? The spike in anthropogenic warming from N20 and CH4 could likewise be timed with the massive intensification of agriculture enabled by large-scale application of nitrate fertilizer and changes in land use patterns (deforestation) accompanying the green revolution since the 1970s. This was a time that was also accompanied by dramatically increased diesel tractor and diesel vehicle use, skyrocketing bunker fuel emissions from the expansion of container shipping, and rising heating oil emissions from a switch from coal to oil, which could account for much of the rest of the increase in N20, much of the tropospheric O3, and a large part of the fine particulate emissions increases. The timing of the acceleration of warming would also strongly imply a weaker climate sensitivity to C02 forcing and a greater cumulative forcing of these other greenhouse gasses. It was, after all, in the 1980s and 1990s that global warming really accelerated, not earlier. Would that not also align well with the much stronger warming over the poles (mostly accounted for by CFCs, HFCs, N20, tropospheric O3), strong stratospheric cooling from the depletion of/hole in the polar stratospheric 03 layer, and the much weaker than expected tropical upper tropospheric temperature anomoly and the weaker than expected deep ocean warming?


    [DB]  In the early 20th century human activities caused about one-third of the observed warming and most of the rest was due to low volcanic activity. Since about 1950 it's all humans and their activities.

    Off-topic and sloganeering snipped.  Arguments pertaining to Climate Sensitivity is Low must be placed on that thread, not here.

  2. Poorly understood and misrepresented papers? Which papers have I not understood? The paper by Unger et al. in the proceedings of the US National Academy of Sciences (citing work by the Fourth Assessment working group of the IPCC) that tropospheric O3’s direct cumulative radiative forcing when combined with fine particulates like black carbon may outweigh that of all the CO2 released since the beginning of the industrial era


    [DB] Off-topic and moderation complaints snipped.  You are essentially arguing one of the many subsets of arguments that "It's not us".  Pick one of the most-appropriate and repost this line of reasoning there.

    Please note that posting comments here at SkS is a privilege, not a right.  This privilege can be rescinded if the posting individual treats adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.  One of the most important of these precepts is to stay on-topic.

    Please take the time to review the policy and ensure future comments are in full compliance with it.  Thanks for your understanding and compliance in this matter.

  3. What the science does not say:

    "CFCs contribute to global warming at a small level."


    [DB] Per the AR5, Halocarbon (which includes CFCs) radiative forcing (RF) is small relative to that of CO2 RF.

  4. This is clearly outdated. Polvani et al. showed that ozone depleting chemicals alone account for 1/3 of all anthropogenic global warming between 1955-2005. The papers I cited above all show that anthropogenic, CH4, N20 O3, and black carbon contribute more than previously thought. I don't understand why these far more potent anthropogenic greenhouse gasses/particles get relegated to relative insignificance, not least since CFC, HFC, SF6, tropospheric O3, N02, and black carbon have unambiguous anthropogenic sources. Increased ppm of C02 is also anthropogenic, but you can't impute the kind of radiative forcing and amplification feedbacks to it and not apply those to these even more potent greenhouse gasses, otherwise there would have been far more warming than we have been able to measure. Something has to give up some radiative forcing in oder to get anything like the warming we have been able to measure. The underappreciation of CFCs and other GHGs is likely why climate models have been running hot. Michael Mann is himself aware that there are problems with the climate forcing theories. He coauthored a paper in Nature Geophysics in 2017 ( that argued that the failure of climate models to align with the measured level of tropospheric warming since 2000 is unlikely to have been caused by natural variability and model error in climate sensitivity but rather in “systematic deficiencies in some of the post-2000 external forcings used in the model simulations.“



    [DB]  Research shows that climate models are getting future projections right, meaning that the physics of the models are well-validated by subsequent observations.

    Models are spot-on

    Sloganeering snipped.

  5. Do note that the paper discussed above Polvani et al (2020) 'Substantial twentieth-century Arctic warming caused by ozone-depleting substances' has been the subject of some corrections. And for the record, I would answer the question of EGS @17 "Would that not be evidence that climate sensitivity to CO2 must be much lower than previously modeled?" with a flat "No!"Given the comment thread since, I'm not sure that any explanation would be helpful.

  6. The total anthropogenic radiative focing bars at the bottom of the chart align almost perfectly with what economic historians know about diesel and heating oil emissions, nitrate fertilizer use, methane emissions from farming, deforestation and stock rearing, and industrial halocarbon use. 


    [DB]  Please take discussions of animal agriculture to this thread.

  7. EGS @29,

    You say "The papers I cited above all show that anthropogenic, CH4, N20 O3, and black carbon contribute more than previously thought." I thnk you will find that is incorrect.

    Consider you CH4 reference cited @17, Hmiel et al (2020) 'Preindustrial 14CH4 indicates greater anthropogenic fossil CH4 emissions'.This paper argues that FF emissions of CH4 were greater than previously thought. The atmospheric burden of CH4 is not challenged and it is the atmspheric burden that determines the climate forcing, not the source of the emissions that increase that atmospheric burden.

  8. MA Roger,

    The atmospheric burden of CH4 has increased. According to NOAA the CH4 mole fraction has increased from 1650 ppb to nearly 1900  ppb between 1980 and 2020. It stabilized around 2000-2005, but has been increasing at a linear rate since then

    Are you disputing that the increased atmospheric concentration of CH4 is not from livestock rearing, farming, and deforestation? And while FF emissions of CH4 are technically not anthropogenic, oil and gas drilling and hard rock mining are releasing it into the atmosphere. 


    [DB] Off-topic snipped.

    Please note that posting comments here at SkS is a privilege, not a right.  This privilege can and will be rescinded if the posting individual continues to treat adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.

    Moderating this site is a tiresome chore, particularly when commentators repeatedly submit off-topic posts or insist on repeating points already refuted. We really appreciate people's cooperation in abiding by the Comments Policy, which is largely responsible for the quality of this site.
    Finally, please understand that moderation policies are not open for discussion.  If you find yourself incapable of abiding by these common set of rules that everyone else observes, then a change of venues is in the offing.

    Please take the time to review the policy and ensure future comments are in full compliance with it.  Thanks for your understanding and compliance in this matter.

  9. EGS @33 ,

    You have a very strange definition of "anthropogenic" if you are not including FF-related emissions of CH4.  Please stick with standard English !

    The IPCC summary in AR5 (based on approx 2010 info) on CH4 and other drivers, seems quite straightforward and comprehensive.  Easy to make a small extrapolation ~ which does not support your radical contention on halocarbons.

    The Hmiel et al. (2020)  paper is relevant and interesting.  (Thanks for that one, MA Rodger.)

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