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Climate Hustle

CFCs contribute only a fraction of global warming

What the science says...

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Models and direct observations find that CFCs only contribute a fraction of the warming supplied by other greenhouse gases.

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).

But let's dig into the details of the paper to see how Lu built his case and where he went wrong.

Unphysical Curve Fitting, Misrepresenting Cited Research, and Circular Logic

Here at Skeptical Science we have previously examined several cases of curve fitting.  This describes the practice of scaling several variables without any sort of realistic physical constraint until the model closely matches the observational data, and then declaring that you've proven that those variables caused the changes in the observations.  Loehle and Scafetta used this strategy to blame global warming on astronomical cycles, and Roy Spencer used it to blame global warming on ocean cycles.

In this paper, Lu used curve fitting to blame global warming on a combination of solar activity and CFCs.  First he randomly scaled a total solar irradiance (TSI) reconstruction to match the surface temperature record as closely as possible.  He claimed that this practice was justified by Solanki and Krivova (2003).  Lu says:

"...it can be seen that the global temperature indeed closely followed the TSI variation up to 1970; the y-axis for TSI can be scaled so that the magnitudes of the temperature and TSI variations are similar during 1850-1970. This was actually shown previously by Hoyt and Schatten50 and Solanki and Krivova52, and an excellent linear correlation with coefficients of 0.83~0.97 between the TSI and the temperature was obtained.52 This implies that the TSI values can be converted into temperatures using the linear correlation.52 The observed data indicate that the solar effect played the dominant role in climate change prior to 1970."

"We have shown that even in the extreme case that solar variability caused all the global climate change prior to 1970, it cannot have been responsible for more than 50% of the strong global temperature rise since 1970 through any of the channels considered here. We believe that even this fraction is too high."

There is a proportional relationship between changes in TSI and changes in surface temperatures, but it's a physical relationship.  You can't just choose whatever proportionality is convenient for your argument.  In fact what Lu has done is assume that TSI explains most pre-1970 global surface warming, and then claim that he's proven this is the case.  It's circular logic, like fixing a card game and then claiming you're a great card player when you win.

The only reason Lu's TSI model matches the surface temperature data is because he forced it to match through curve fitting – by refusing to apply any physical constraints to his model.  Then when his unphysical model fits the temperature data reasonably closely, he declares that he's shown "that the solar effect played the dominant role in climate change prior to 1970."  In reality he's shown no such thing, he's simply assumed that his conclusion is true.

Lu also uses a solar reconstruction from Hoyt and Schatten (1993) in his curve fitting exercise.  Why use the results of 20-year-old study?  Perhaps because it helps Lu arrive at his end conclusion that global warming isn't due to CO2.  The Hoyt and Schatten paper claims that the equilibrium climate sensitivity to doubled CO2 is a mere 0.19°C – a factor of 15 lower than today's best estimates.

Perhaps the gold standard of TSI reconstructions comes from Wang, Lean, and Sheeley (2005), updated by Kopp and Lean (2011), whose data are available here.  They estimate that the increase in the amount of solar radiation reaching Earth from 1860 to 1970 was not very large (a radiative forcing of less than 0.2 Watts per square meter, compared to the 1.7 Watts per square meter CO2 forcing from pre-industrial times to Present), and only sufficient to account for approximately 0.07–0.15°C average global surface warming.  Thus TSI can probably only account for less than half of the observed 0.3–0.4°C surface warming during that time, contrary to the 100% solar attribution Lu claims based on his curve fitting exercise.

Yet More Circular Unphysical Arguments, Curve Fitting, and Misrepresentation of Cited Research

Lu faced the conundrum of having to explain how the increased greenhouse effect from CFCs can cause global warming while the much larger increased greenhouse effect from rising CO2 can't.  To accomplish this, he used what the climate scientists at RealClimate have described as the saturated gassy argument – claiming that increased CO2 can't cause more warming because there is already so much in the atmosphere that its greenhouse effect has become saturated.  However, as the climate scientists at RealClimate (and we at Skeptical Science) have explained, that argument is quite clearly wrong – disproven by observational data.

Perhaps worse, Lu claimed that a paper by Anderson et al. (2004) supported his saturated gassy argument, claiming the CO2 absorption band is missing from the observed spectrum data.  On the contrary, Anderson et al. concluded,

"The spectra in Fig. 8a are the result of a superposition of two different effects. First, there is an increase of greenhouse gases from 1970 to 1996 that gives rise to recognizable bands in the observed spectrum..."

And once again, Lu tried to demonstrate that CFCs can account for the recent global surface warming through unphysical curve fitting, multiplying the CFC forcing by whatever value allowed the CFC data to best fit the temperature data.  When using physical constraints, CFCs (included in "halocarbons" in Figure 2) can account for only about 20% as much warming as CO2.

AR4 forcings

Figure 2: Global average radiative forcing (RF) in 2005 (best estimates and 5 to 95% uncertainty ranges) with respect to 1750 for CO2, CH4, N2O and other important agents and mechanisms, together with the typical geographical extent (spatial scale) of the forcing and the assessed level of scientific understanding (LOSU).  From the 2007 IPCC report.

In his Figure 11, Lu also exaggerates the difference between expected CO2-caused warming and observed temperatures by plotting the observational data against the surface warming we expect at equilibrium.  This is wrong because there is a global energy imbalance, which means there is more warming "in the pipeline" for several decades to come before we reach that equilibrium state.  In reality the Earth has warmed as expected from the increased CO2 greenhouse effect.

In Nuccitelli et al. (2014), we also found that even ignoring the unphysical "curve fitting" in his model, models using current known human climate forcings produced a more accurate fit to up-to-date surface temperature measurements (HadCRUT4) than Lu's model (r2 of 0.81 vs. 0.72).

Nuccitelli et al. (2014) Fig 1

Replication of Lu (2013) Figure 12 using more recent data and a realistic response function. The fit between the anthropogenic forced response (black dashed line) and adjusted temperatures (red squares) is superior to the fit to CFC forcing (green solid line), even allowing for an additional unphysical scaling and lag as in Lu (2o13) (green dashed line).

Ultimately the 'CFCs are driving global warming' myth from Lu (2013) is based on assuming rather than proving the hypothesis, unphysical curve fitting, and misrepresenting the cited research.

Last updated on 14 April 2014 by dana1981. View Archives

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Comments

Comments 1 to 13:

  1. Lu 2009, full version in pdf, postulated that ozone loss is driven by that other catch-all of CO2 deniers, the much-maligned cosmic rays. Here's their prediction:

    The intensity of cosmic rays is still peaking in 2009, so we should expect to observe one of the deepest ozone holes over the spring Antarctica in 2009-2010.

    The data for the Antarctic ozone hole are available here. Sept 2009 had a max hole area of 24 million km^2, smaller than nearly every prior year back to 1992. Sept 2010 was 22.2 million km^2.

    The ozone hole is shrinking during peak cosmic ray intensity? Ooops.

    That their mechanism turned out to be incorrect makes further predictions suspect:

    The CRE-driven ozone depletion is expected to decrease after 2010 due to the CR cycles, but the EESC will keep decreasing ... . If the above observation is confirmed, then we expect to observe a continued decrease in global surface temperature - 'global cooling'. That is, global warming observed in the late 20th century may be reversed with the coming decades. Indeed, global cooling may have started since 2002 ...

    This is supposed to be credible?
  2. Sorry to discover this one a little late in the piece, I fully concur that it is incorrect to blame AGW entirely on CFCs, but I do think the contribution of the Montreal Protocol to reducing climate change is under recognised - both in terms of the abatement achieved to date by phasing out consumption of CFCs, and what it could yet do by financing recovery of ozone depleting CFCs and HCFCs, and by expanding its scope to address rapidly increasing HFC emissions.

    The best paper explaining this in the literature is Velders et al (2009) and briefing papers by the Environmental Investigation Agency are well worth reading in order to track this issue.

    The importance of looking at the 20 year Global Warming Potential values of HFCs is highlighted in this previously unpublished graph, which has recently been included in a Greenpeace International paper here.

    As the experience of getting rid of CFCs shows, this is a relatively easy task compared with abating CO2 emissions. While this remains of paramount importance, we are about to make the problem a whole lot worse if we continue to fail to take swift and serious action to prevent the projected volume of HFC emissions from occurring.


  3. Lu has published another related article: http://journalofcosmology.com/QingBinLu.pdf

    Any comments on it, or on his claim that CO2 traces and temperature traces don't match for the years 1850-1930 or for his reported CO2 concentrations of 285-310 ppm? It seems to be in contradiction to other data on this site:
    http://www.skepticalscience.com/pics/Comparison.png

    Forgive me if these are questions that have been answered before, I'm new to the site. If they have been answered I'd appreciate being pointed to them.
  4. And another paper by the same authour, just published in International Journal of Modern Physics B

    Cosmic-Ray-Driven Reaction and Greenhouse Effect of Halogenated Molecules: Culprits for Atmospheric Ozone Depletion and Global Climate Change

    http://www.worldscientific.com/doi/abs/10.1142/S0217979213500732

    and

    https://uwaterloo.ca/news/news/global-warming-caused-cfcs-not-carbon-dioxide-study-says

  5. Ah, yes, the International Journal of Modern Physics B, the journal that is supposedly focused on condensed matter, statistical, and applied physics, the journal that published the amazingly wrong Gerlich & Tscheuschner paper. 

    A new paper in which the author claims that CO2 forcing is saturated, that the log relationship between concentration and forcing for CO2 no longer holds. Oh my...

    I would suggest taking climate papers from IJMPB with a large grain (perhaps a block?) of salt.

  6. His newest paper is making the rounds quickly today it seems. Many thanks John, this argument certainly helped the debunking process

  7. Eli Rabett has commented on the "new" (i.e., recycled) 2013 Lu paper claiming CFCs are responsible for everything.

  8. An updated rebuttal of the CFC theory needs to be on the homepage ASAP. Some mainstream media are throwing the ridiculous claims made in Lu's new study around as if they were facts (notably The Australian).

  9. David Karoly pointed out that the HFC replacements for CFCs have just as much greenhouse effect as CFCs, so the reduction in CFCs that Lu insists has been and will cause cooling, is being offset by HFCs.  So Lu's assertion is just plain wrong for that reason, too.

  10. As much as it pains me to correct such an eminent and respected scientist, I must humbly submit that Prof David Karoly is mistaken in saying on the ABC radio "AM" story cited by Tom @9 that "The replacement chemicals for chlorofluorocarbons are hydrofluorocarbons, which are used as refrigerants, have already got as large a greenhouse influence as the reductions in the chlorofluorocarbons. 

    As established by Velders et. al. Science (2012) "Preserving Montreal Protocol Climate Benefits by Limiting HFCs"  (and reinforced by the 2011 UNEP Synthesis Report "HFCs: A Critical Link in Protecting the Climate and the Ozone Layer" ) the climate benefit inadvertantly acheived by phasing out CFCs to protect the ozone layer has been significant, yet is likely to be lost in coming decades if we fail to take effective action to prevent rapidly rising emissions of HFCs. The HFCs horses have not yet all bolted, but it is time to shut the gate.

    Velders et.al., Science (2012)

    Velders et.al. (2012) put it like this: "Total avoided net annual ODS emissions are esti- mated to be equivalent to about 10 Gt CO2/ year in 2010, which is about five times the annual reduction target of the Kyoto Proto- col for 2008–2012 (5). This climate benefit of the Montreal Protocol may be reduced or lost completely in the future if emissions of ODS substitutes with high GWPs, such as long- lived HFCs, continue to increase."

    Preserving the climate benefits of the Montreal Protocol by urgently phasing out HFCs with a mix of policy tools including strict regulation such as end use bans, carbon pricing levies and inclusion in the Montreal Protocol to drive concerted global action is the largest, quickest, cheapest and most effective tool in the emissions abatement policy shed. But as atmospheric HFC concentrations continue to rise, time is running out, and greater attention to the non-CO2 forcers is required now.

    Natural refrigerants such as ammonia, carbon dioxide and hydrocarbons stand ready to provide the needed solutions to meet our cooling needs, and the chemical companies that caused the CFC, HCFC and HFC problems have a new range of patented and attractively branded low-GWP 'HFO's' they are pushing to see adopted by anyone who still thinks they deserve to continue to be rewarded for doing so.

    Prof Karoly is completely correct in saying "in fact, the global warming influence of these chemicals, the hydrofluorocarbons, is already growing more rapidly than the reductions in chlorofluorocarbons" (although he could have added that hydrochlorofluorocarbons, HCFCs, are also CFC replacements and are still rapidly increasing, in spite of being subject to a Montreal Protocol driven phaseout), but there is still more we could do to increase the reductions of CFCs & HCFCs by recovering them from the pipework and foams of our dead fridges and airconditioners respectively.

    Lamentably few scientists understand the climate threat posed by HFCs, and fewer still are prepared to speak out about the need to urgently avoid their use and to rapidly embrace the readily available environmentally benign rerigerant solutions.

    If we are to avoid the projected greenhouse impacts of HFCs wiping out those acheived by the CFC phaseout, it would be very helpful if Prof Karoly and others of similar standing were able to assist in clarifying the imperative of acting now to rapidly reduce the use and emissions of Ozone Depleting Substances and Synthetic Greenhouse Gases.

    While Lu is completely wrong about CFCs, the debate now required is a good opportunity to correct the widely held yet mistaken notion that the F-gas problem is fixed.

  11. Further to the above @10, I hope the following graphs may be of interest:

    These Velders figures illustrate well the 'world avoided' by the Montreal Protocol CFC phase out (and the accelerated HCFC phaseout agreed in 2007), and the HFC projections by volume and CO2-e impact. While not at this stage likely, reducing HFC emissions well below the "low" projection is certainly possible with available technology and a lot more public awareness and political will.

    Climate Impacts of ODS & SGG

    This figure from the 2011 UNEP Synthesis Report "HFCs: A Critical Link in Protecting the Climate and the Ozone Layer" provides a good overview of where we've come from and where the relevant literature indicates we are headed, absent a more informed policy debate and resultant policy and market responses.

    Figure 3.2 UNEP HFC Synthesis Report

  12. Apologies, the figure above with 3 graphs was adapted from Velders et.al. (2007, 2009), but it is actually figure 5-6 from the Scientific Assessment of Ozone Depletion: 2010, a collaboration of WMO, UNEP, NOAA, NASA & EC, see page 5.29 for associated explanation.

  13. GreenCooling:  Mario Molina et.al. noted in 2009 in Reducing abrupt climate change risk using the Montreal Protocol and other regulatory actions to complement cuts in CO2 emissions which was published in pnas that:

    "The Montreal Protocol is widely considered the most successful environmental treaty, phasing out almost 100 ozone-depleting chemicals by 97% and placing the ozone layer on the path to recovery by mid-century (18). It also is the most successful climate treaty to date..."

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