Murry Salby: CO2 is the integral of temperature

...in the past, on short timescales, it has therefore fluctuated rapidly...

Honza [=Jan] U. sent me the following one-hour April 2013 talk by Prof Murry Salby of Australia's Macquarie University:



This astrophysicist and atmospheric scientist has a rather impressive publication record. At the beginning, I was a bit discouraged by Pierre Gosselin's summary that suggested that Salby was making some widespread elementary errors about the direct attribution of CO₂ emissions according to their isotopic composition (the extra CO₂ we see in the atmosphere generally has a very different composition than the CO₂ when we emitted it, because the carbon is being quickly recycled all the time while chemistry doesn't care about the differences between isotopes but it's still true that our additions of CO₂ have increased the CO₂ concentration).

But I was wrong, Salby isn't doing these particular trivial mistakes and when I ultimately listened to the talk, it looked rather impressive.




He employs various types of statistical models, Fourier transformations, and other things to decode the relationships between CO₂ and the temperature. Of course, the temperature is mainly the driver of CO₂ and CO₂ follows – to say the least, that's the dominant relationship during the glaciation cycles (the time scales from tens to hundreds of thousands of years).

Those things wouldn't be new and I wouldn't listen to another 1-hour talk that just discusses whether CO₂ was the cause or the consequence during glaciation cycles. Of course it was the consequence. Whoever still acts as if he were misunderstanding these basic issues is either a hopelessly brainwashed moron or an amazingly dishonest demagogue or both.

But Salby said much more than that.




He argued that the anomalous CO₂ concentration may be approximated as the integral of the anomalous temperature, \[

\Delta\,{\rm conc}(CO_2) = \alpha \int \dd t\,\Delta T

\] which sort of explains why it seems to be rising so smoothly (if we ignore the nearly periodic seasonal variations). But Salby has also presented some evidence that the ice record heavily underestimates the fluctuations of the CO₂ concentration, especially the high-frequency (short-period) oscillations that occurred a long time ago. If that's true, it's pretty likely that concentrations above 400 ppm may have been rather mundane even before the industrial activity.

Using the Fourier methods, he argues that there is a phase shift of 90 degrees between the temperature and CO₂ pretty much at all frequencies. I am not quite seeing how this may be true because at least in the glaciation cycles, i.e. at the 10,000-year time scale, these two quantities are pretty much in sync. How does the phase shift move to 90 degrees for shorter time scales?

And his discussion of the different isotopic composition (C12 vs C13) of the fossil fuels and the present plant life is sophisticated, not the kind of silly caricature I was led to expect. At any rate, Salby concludes that the excess CO₂ is caused by the integrated or accumulated positive temperature anomaly in 1920-1940 and 1980-2000 or so and these positive anomalies may be interpreted as noise, not results of any trends.

That sounds nice except that I think it's obvious that the CO₂ we have added to the atmosphere has led to some increased CO₂ concentrations and the latter increase is comparable to 50% of the former (airborne fraction etc.) – it's not negligible. It doesn't matter that there are 50 times more important contributions to the CO₂ atmospheric budget as well. Despite these dominant contributions, a small surplus simply can't become completely invisible.

If you were thinking whether you should listen to that talk, my recommendation is probably Yes. Despite the fact that he is trying to deny some obvious facts – if I understand the discussion about the attribution of an elevated CO₂ well and if I am right about its imperfections – he is also saying lots of new things and offering many sophisticated methods that you may want to know about.

At the end, Salby offers some criticisms of the climate models that I only partly agree with. Concerning the agreeable conclusions, he says that the prevailing climate models show CO₂ and the temperature essentially as the same thing; in the real world, they're not the same thing at all. These two claims – and their paramount contrast – are self-evidently true.

To mention the propositions I don't quite share, he says that theories can't ever be tested against the past data; tests of predictions of the future are always needed. I disagree with that. It's a historical coincidence whether some data were collected before a theory was written down or after that. A theory is always constructed or chosen according to the data in the past and then it gives predictions for other phenomena as well. Those phenomena may be data to be collected in the future but also additional data that may be collected about the past. Regardless of the timing, such data may be used to strengthen or weaken our confidence in the theory (or rule it out).

See also replies by MeteoLCD (more detailed review than mine!), Anthony Watts' 100+ commenters, The Hockey Schtick, Climate Depot, Tall Bloke, and – from the crazy side of the aisle – John Cook (I agree with some of the criticism) and Deltoid who calls Salby "unhelpful" (for "the cause") LOL. ;-)