Murry Salby has now completed his tour of Britain and there have been a few posts discussing his presentations. Some positive, others not. I’ll be quite honest and say that I think Salby’s ideas are scientifically incorrect and that it’s not difficult to show this. Hence, I do have an issue with those who seem to think that he might have a point. It implies, in my opinion at least, either too much wishful thinking or a lack of willingness/inability to actually determine whether or not his ideas do have merit. I apologise to those who think this may be an unfair way to start this post, but I am more than willing to be proven wrong.
Scottish Sceptic has, however, written a report on Salby’s lecture in Edinburgh. Given my never-ending optimism, I thought I might write a few brief posts addressing some of what is said in Scottish Sceptic’s review of Salby’s talk. Maybe I should comment directly on his post, but it does seem easier to simply write this post of my own. A pingback should appear there and I’ll leave a comment pointing out that I’ve addressed some what is raised in the post.
What I’m also going to try and do is keep it fairly simple, by only addressing one point at a time. If this seems to work and if the outcome is positive/constructive, I may write more. If not, I can simply stop. What I thought I would address in this post is what Scottish Sceptic regards as one of the key graphs. It’s shown below and is a plot of atmospherice CO2 concentrations and temperature anomaly, from 1960 to today. The claim is that this graph shows that there isn’t a good correlation between rising atmospheric CO2 levels, and rising surface temperatures.
There are two main issues with this interpretation. One is that rising atmospheric CO2 concentrations act to reduce the amount of outgoing longwave radiation, increasing the amount of energy in the climate system. Only a few percent of this energy is associated with heating the surface. You really should be comparing the rise in atmospheric CO2 with the rise in total energy, not only with the rise in surface temperature. Furthermore, because the rise in surface temperature is only associated with a few percent of the energy excess, it is very sensitive to internal variability and other factors. Hence, we don’t really expect the surface temperatures to rise smoothly, even if the atmospheric CO2 concentration is rising smoothly. Additionally, there are factors (such as anthropogenic and volcanic aerosols) that can also influence how much energy is being trapped in the climate system, and so we wouldn’t even expect a perfect correlation between the rise in atmospheric CO2 and the rise in total energy (on short timescales at least).
The second issue relates to how much we might have expected surface temperatures to have risen given a certain rise in anthropogenic CO2. The change in adjusted forcing, ΔQ, when the CO2 concentration changes from Co to C is
The figure above considers the period 1960 to today, during which time CO2 concentrations changed from 310ppm to about 390ppm. This implies a change in adjusted forcing of 1.23 Wm-2. The expected change in temperature would be determined by the transient climate response (TCR) which is expected to be about 1.5oC per doubling of CO2. A doubling of CO2 also produces a change in forcing of ΔQ2x = 3.7Wm-2. The expected temperature change is then
This suggests that the expected change in surface temperature since 1960 is about 0.5oC. Therefore, if you really want to compare changes in atmospheric CO2 and surface temperatures, you really should ensure that the two y-axes are scaled properly. The right-hand y-axis scale in the figure above is 1.3oC and makes it appear that surface temperatures have risen slower than expected when, in fact, it’s pretty close to what would be expected.
So, essentially I don’t think this figure really illustrates what Murry Salby is claiming. Not only do we not expect a particularly good correlation between the rise in atmospheric CO2 and surface temperatures, the actual rise in surface temperatures since 1960 is entirely consistent with a TCR of about 1.5o. There’s my comment number 1. Feel free to comment here and I will also do my best to address constructive comments either here or on Scottish Sceptic’s original post.