There’s a new post on Watts up With That (WUWT) by Dr Vincent Gray in which he extols the virtues of Roy Spencer and Murry Salby. I’ve already discussed the virtues of Roy Spencer in a previous post, so I won’t say more here.
What about Murry Salby though? Well, according to this post Murry Salby is a very clever bloke who
begins by showing the paleo record based on ice cores and shows that there is a close correlation between carbon dioxide and temperature, with temperature coming first. The same applies to methane.
He then attaches it to the more recent CO2 record and plots the Carbon13 figures, which declined over the whole period. Since plant material prefers C12 this means that the additional CO2 comes from plant material. The IPCC claims that the additional plant material must come from combustion of fossil fuels, so this is their “Smoking Gun” that the increase in CO2 is caused by human-derived emissions.
In paleo records, temperature does indeed lead CO2 rises, nothing there that challenges anthropogenic global warming (AGW) today. The main point is that the CO2 then amplifies the temperature rise and produces much larger temperature changes than could be explained by whatever was driving the initial rise (Milankovitch, for example). What about the second part of the statement above?
Well, the basic idea is that when plants grow, they preferentially use carbon-12, rather than carbon-13. Hence, the ratio of carbon-12 to carbon-13 is higher in plants than in the atmosphere. What Murry Salby is claiming is that since the carbon-13 fraction in the atmosphere has been dropping while CO2 concentration have been rising proves that it must be due to plants and is not due to our use of fossil fuels. In a sense he’s correct. It is due to plants. It’s due to plants that existed millions of years ago and have since turned into fossil fuels. It isn’t due to plants today.
What else does Murry Salby claim? Well he
then provides data and graphs which show that the additional CO2 results from what happens during a temperature fluctuation, using the satellite (MSU) temperature record since 1978. He shows that the CO2 which is released by a temperature increase is always greater than the CO2 absorbed when the temperature falls, providing a net increase in the atmosphere.
Indeed, he’s correct. As the surface temperature fluctuates, this drives fluctuations in the CO2. You can look it up and see for yourself. What Murry is claiming is that the amount that is added when the fluctuation rises exceeds the amount lost when the fluctuation drops and hence explains the rise. Indeed, in some sense, once again true. Why is this? Well it’s because, on top of these fluctuations, there’s an addition of CO2 to the atmosphere through our use of fossil fuels. What we have is fluctuations due to annual temperature variations plus a longer-term trend due to our use of fossil fuels. Just because one can associate temperatures variations with rises in CO2 doesn’t mean that all CO2 variations must be due to temperature variations.
This is the same logic as that used by Bob Tisdale who claims that because he can associate variations in the temperature record with ENSO cycles, that all the warming must be due to these cycles. Now Bob Tisdale has, as far as I’m aware, no actual scientific training, so maybe this is excusable. Murry Salby is, however, a Professor of Climate Science at Mcquarie Univerity so I find it more difficult to excuse his flaws in logic than I would those of Bob Tisdale.