Matt Ridley, who regards himself as a rational optimist, had an OpEd in the Wall Street Journal yesterday titled Science is about evidence, not consensus. Indeed, I agree, I just think that what Matt Ridley suggests in his article is, at best, a strawman argument.
Phil Plait very nicely rebutted Matt Ridley’s article in a Bad Astronomer post called You’re Getting Warmer: Another Wall Street Journal Global Warming Article Misses the Target. Matt Ridley has now updated his own blog to rebut Phil Plait’s rebuttal, but sadly seems to simply reinforces his own ignorance. There’s something that I suspect I will be repeating many times on this blog and it is this: if you think you’ve noticed something that a large number of professional, highly-trained, experienced scientists have missed, you should typically take a large step back and consider the possibility (quite likely) that you are the one who is mistaken, not the scientists.
So, what does Matt Ridley claim. He quotes Phil Plait and then adds
“First, it’s true that in the distant past (hundreds of thousands of years ago) a rise in carbon dioxide sometimes did follow a rise in temperature.” Actually, this is invariably the pattern in the ice core record, not “sometimes”.
I believe Phil is correct. The Vostok ice core is from Antarctica and in this ice core temperature leads CO2. However, I believe that there are Arctic ice cores for the same period in which CO2 leads temperature. So, CO2 doesn’t always lag temperature. I should probably try and finds these, but have to go and give a lecture in 20 minutes, so happy to be corrected if I’m wrong.
Matt goes on to say,
the inconvenient truth is that at the end of the Eemian interglacial temperature fell steadily for thousands of years before CO2 levels fell at all. The argument that a small warming at the start of an interglacial causes a CO2 release which causes a large warming is one that has been tested and found entirely wanting.
So, yes at the end of the last interglacial the temperature did fall quite quickly while CO2 levels dropped more slowly. However, what Matt Ridley seems to think is that the argument is that a small temperature change driven by orbital variations is then amplified significantly by increased atmospheric CO2 concentrations. During the Milankovitch cycles, temperatures varied by about 10oC. The CO2 forcing varied by about 3 Wm-2. Given an equilibrium climate sensitivity of about 3oC per doubling of CO2, this implies that the CO2 contributed 2 to 3oC of the warming (maybe 30% of the total). The total temperature change cannot be explained without including the influence of CO2, but CO2 wasn’t – as far as I can tell – the dominant forcing. Also, the variation of solar insolation is not nice and simple across the Milankovitch cycles. Sometimes the change is large and rapid, other times smaller and slower. The Eemian may simply be a period where the solar forcing dropped quickly by a large amount and it simply took much longer for the CO2 levels to drop.
Matt Ridley then adds
If we assume that the CO2 is giving 3° per doubling of warming per the IPCC hypothesis, then the problem is that raises the rate of thermal outgassing up to 17 ppmv per degree of warming instead of 15 ppmv. This is in the wrong direction, given that the cited value in the literature is lower at 12.5 ppmv.”
This comes from this Watts Up With That (WUWT) post. During the Milankovitch cycles CO2 varied between about 180 and 280 ppm and the temperature changed by about 10oC. The WUWT post estimates that CO2 increased by 15ppm for every 1oC of warming, quite close to other estimates of 12.5ppm for every 1oC. Matt Ridley seems to have confused the thermal outgassing with the radiative forcing.
Matt Ridley then goes on to criticise Phil Plait for mentioning Michael Mann’s hockey stick and the more recent paper by Marcott et al., both of which – according to Matt – have been discredited. No they haven’t. The hockey stick shape has been recovered in many independent studies including the most recent that involved 78 researchers, from 24 different countries, 60 different institutions, and which used 511 proxies. When Steve McIntyre tried to discredit Michael Mann’s hockey stick, he apparently forgot to remove the hockey stick from what he claimed was simply random noise. When Steve McIntyre recovered hockey stick shapes from his test data, he claimed that this indicated that one could get hockey stick shapes from random noise. Maybe, but only if the random noise already has a hockey stick shape in it. There are numerous blog posts that have attempted to discredit the Marcott et al. work but, as far as I’m aware, none have actually done so, despite the clear desire for this to be true.
So, this has got rather long, but as far as I can tell, the rational optimist is somewhat irrational when it comes to interpreting the evidence for anthropogenic global warming. Maybe he should spend a bit more time talking to actual climate scientists rather than relying on Watts Up With That and Climate Audit, neither of which are particularly well regarded within the climate science community.