Two things came together today. First was A Guide to Understanding Global Temperature Data by Roy Spencer, which I read a week or so ago. Second, I was pointed to an article in the Guardian in which a white paper written by the same Roy Spencer was being rebutted.
Initially, it was not clear which paper was referred to and, although there were also 13 questions involved, the rebutted items didn’t seem to be similar to the guide that I read earlier. So I was a bit confused. Did Spencer wrote another white paper in which he also used that 13-questions format, but with other arguments?
Becoming curious, I went back to the beginning of the article to look for the source, and surprisingly, when I clicked the link of the white paper, the Guide to Understanding Global Temperature Data popped up. Strange. The white paper that the Guardian was rebutting, seems to be the exact same paper that I read a week ago…
The author of the article, Dana Nuccitelli, claimed that the arguments in the guide were an example of a Gish Gallop and therefor too time-consuming to rebut. Therefor he pointed to the Climate Myth database that was compiled by Skeptical Science and in stead of rebutting the arguments in the white paper, he just linked to entries in that database.
So far, so good. Let’s start with how the first argument was rebutted:
1) ‘Carbon dioxide is a trace gas’ is rebutted as Myth #127.
That was odd. I didn’t recognize this being one of the arguments that Spencer used in his guide, yet here the answer on question 1 seems to be reduced to “Carbon dioxide is a trace gas” and was rebutted as such. Meaning as if was being said that CO2 couldn’t have important effects because it is a trace gas in the atmosphere.
That didn’t make much sense. I read several writings from Roy Spencer before (including the guide at issue) and it was not my impression that he thinks that CO2 could not have much effects “because it is a trace gas”. So I went back to the guide and read the arguments of that first question again to see what Spencer actually wrote. By the way, that first question is: “Does an increasing CO2 level mean there will be higher global temperatures?”.
This is where I think is the critique of the Guardian is based on:
The following plot of the CO2 increase at Mauna Loa shows that even though the increase seems substantial in relative terms (left panel), the amount of CO2 in the atmosphere is so small in absolute terms that the change in concentration is not even visible in a plot (right panel) where percent, rather than parts per million, is used for the vertical scale.
In fact, most people are surprised to learn that humans have so far contributed only about 1 molecule of CO2 to every 10,000 molecules of air over the last 60 years. About 50 percent of all we emit is absorbed by nature, since CO2 is necessary for photosynthesis and for life to exist on Earth.
Although Spencer showed the percentage of CO2 in the atmosphere, nowhere is being claimed that effects of CO2 is small or insignificant because it is just a trace gas. But of course, one could always interprete his comparison of the increase on ppm level with the percentage in the atmosphere as implicitly making such claim. But that would show that Nuccitelli poorly read the paper.
More telling however is how it was rebutted. Let’s go to Myth 127 at the Skeptical Science website:
I could agree that if is being said that human emissions have no impact because they are only a small portion of a trace gas, this would be a logical fallacy. The fact that a substance is a trace element doesn’t say anything about its impacts, even in very small amounts.
Skeptical Science builds its case by giving a whole bunch of analogies with other substances that have strong effects in small doses. Like for example Arsenic that can be poisonous even when it is highly diluted. I can dig that. There are many examples of substances that can have strong effects, even in minute concentrations. So far so good. But analogies go only as far as they go.
They continue with “traces of CO2“, in which they state that percentage of CO2 might be a convenient way to talk about the amount of CO2 in the atmosphere, but it is only relative to the rest of the atmosphere and doesn’t give an absolute amount. Which is more important than the percentage. The more molecules of CO2 in the atmosphere, the more heat it can absorb.
Technically, they are of course right. A percentage doesn’t say anything about the absolute amount in the atmosphere and the more in the atmosphere, the more the potential effect. I can understand that, but it is rather linear view where there is no linearity. First, the effects of CO2 are not linear, but logarithmic. The more CO2 is added, the less the additional effect will be. Second, CO2 works in a complex, coupled and chaotic system. Which will give rise to uncertainties of how the system will react.
Spencer seems not to have a problem with the warming effect of CO2, but rather with the certainty in which it is communicated (emphasis by Roy Spencer):
The science supporting some warming effect of more CO2 in the atmosphere is reasonably sound; what isn’t well known is just how much of a temperature rise will result. This uncertainty is tied up in the holy grail of climate sensitivity, which I will address later.
For the time being, suffice it to say that more CO2 in the atmosphere should cause some warming, but the amount of warming is much more uncertain than the public has been led to believe.
So I am at a loss why Nuccitelli classifies Spencer as having claimed that CO2 is “just a trace gas” and therefor can not have large effects.
The rebuttal was based on a misrepresentation of Spencer’s argument. Spencer did not say that “CO2 could not have a large effect because it was a trace gas”. He did said that some warming was to expected, but that it is not yet known “how much” and that the amount was more uncertain than the public has been led to believe.
Finally, the argument that Nuccitelli uses comes not even close in “rebutting” the alleged argument made by Spencer. Skeptical Science just gives a list of substances that can have large impacts in small amounts. Which is true, but not relevant.
What Spencer tells us is that CO2 is a trace gas and that anthropogenic emissions are only a small addition to it. Then follows that CO2 needs to be a very active substance to have catastrophic consequences in such low concentrations. It is not enough to just prove that some substances can be very active. It is necessarily to prove that CO2 is such a very active substance, that even in these concentrations it has a catastrophic additional impact.
The less can be attributed to anthropogenic emissions, the more potent that substance has to be to have a big impact. It is one thing to prove that trace substances can have a large effect, it is a completely different story to prove that anthropogenic CO2 has a large (additional) effect in the quantities as given by Spencer.