Global Warming Can’t Be Blamed on CFCs

21 04 2014
Global warming can’t be blamed on CFCs – another one bites the dust

Nuccitelli et al. (2014) rebuts the argument that global warming is due to chlorofluorocarbon rather than carbon emissions

cosmic rays

Artists impression of cosmic rays entering Earth’s atmosphere. A paper by Qing-Bin Lu argued that cosmic rays are linked to CFCs which are linked to global warming, but both arguments were recently rebutted. Photograph: Asimmetrie/Infn

A paper published in the International Journal of Modern Physics B by the University of Waterloo’s Qing-Bin Lu last year claimed that solar activity and human chlorofluorocarbon (CFC) emissions, not carbon dioxide emissions, could explain the observed global warming over the past century. The journal has now published a rebuttal of that paper by myself and my colleagues Kevin Cowtan, Peter Jacobs, Mark Richardson, Robert Way, Anne-Marie Blackburn, Martin Stolpe, and John Cook.

As I recently discussed, contrarian climate research blaming global warming on Anything But Carbon (ABC) tends to receive disproportionate media attention. Lu’s paper was a prime example, being trumpeted by aUniversity of Waterloo press release and Science Daily and Phys.orgarticles, all of which used exaggerated language like “Lu’s theory has been confirmed.” ABC News did a better job covering the paper, talking to climate scientist David Karoly, who expressed appropriate skepticism about a paper which purports to overturn decades and even centuries of well-established physics and climate science in one fell swoop. Characteristically, Rupert Murdoch‘s The Australian then criticized ABC News for failing to be “fair and balanced” because they interviewed an actual climate expert about the paper.

However, Lu’s paper contained numerous clear fundamental flaws. For one, the underlying argument was based on “curve fitting” or “overfitting,” which is when the variables in a model are arbitrarily stretched to match the observational data. In this case, Lu took the global energy imbalance caused by CFCs (which are greenhouse gases) and scaled them up dramatically to match measurements of global surface temperatures.

Lu then also had to explain why CFCs would be increasing the greenhouse effect, but carbon dioxide wouldn’t. To accomplish this, he invoked what’s known as “the saturated gassy argument” – claiming that rising carbon dioxide can’t cause more warming because there is already so much in the atmosphere that its greenhouse effect has become saturated. This argument was first made by Knut Ångström in 1900, but was conclusively disproved by E. O. Hulburt in 1931 and military research in the 1940s. Lu misinterpreted several recent papers to revive the argument, but as we showed in our paper, it still remains incorrect.

Ultimately Lu’s argument was that global surface warming has slowed in recent years, and his model using CFCs and solar activity could accurately match those observations. However, Lu used outdated and superseded surface temperature measurements with a cool bias that exaggerated that surface warming slowdown. He also used an extremely outdated reconstruction of solar activity. We showed that even ignoring the unphysical “curve fitting” in his model, models using current known human climate influences produced a more accurate fit to up-to-date surface temperature measurements than Lu’s model.

Replication of Lu (2013) Figure 12 using more recent data and a realistic response function. The fit between the climate response to human influences (black dashed line) and global surface temperatures (red squares) is superior to the fit to the CFC temperature influence (green solid line), even allowing for Lu's unphysical scaling (green dashed line).Replication of Lu (2013) Figure 12 using more recent data and a realistic response function. The fit between the climate response to human influences (black dashed line) and global surface temperatures (red squares) is superior to the fit to the CFC temperature influence (green solid line), even allowing for Lu’s unphysical scaling (green dashed line).The extreme curve fitting employed in Lu’s paper is apparent in the above figure, with the solid green line indicating the actual global surface temperature response from the CFC influence, and the green dashed line indicating the response after the arbitrary scaling by Lu. It’s also clear that the temperature response to all human influences (black dashed line) correlates well with the observed temperature changes, with natural influences and internal variability also accounting for some short-term changes, like the surface warming slowdown over the past 10 to 15 years.

Another key flaw that we discussed in our paper was Lu’s failure to account for the entire climate system. Changes in the greenhouse effect don’t only impact surface temperatures; they impact the entire global climate. Thus if CFCs really were the current dominant influence on the global climate, given that they have flattened in recent years (due to the Montreal Protocol), the warming of the entire global climate should also have flattened out. That’s simply not the case, as the oceans have continued to warm at a rate equivalent to about 4 Hiroshima atomic bomb detonations per second during that time. As our paper showed, the fundamental flaws in Lu’s argument are numerous.

*It ignores the continued rapid heat accumulation in the oceans
*It relies on unphysical curve fitting
*It tries to revive the long-debunked saturated gassy argument
*It uses outdated data
*Using known human climate influences dominated by carbon dioxide fits the data better than Lu’s flawed model anyway

Our paper concludes,

“We therefore conclude that the hypothesis of [Lu] is not only inferior to the mainstream explanation of the present climate change, but that it is based on unphysical and fundamentally flawed premises.”

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