(and a little genteel climate iconoclasm)
On March 18th I attended an unusual event: to celebrate its 750th anniversary, Balliol College, Oxford, is staging a series of “Master’s Seminars” around the world, on subjects of global interest. This one, in the European parliament in Brux, was — you guessed it — on Global Warming. Appropriate that an old college should debate an issue that itself is rapidly starting to look like history.
There had been a minor contretemps in the planning. Balliol had assumed that Charles Tannock, who was standing host to the event, would drum up interest among MEPs, while Charles thought the College was on the case. So at the last minute Charles was calling round to rally support. Not entirely successfully: the only MEP I spotted at the seminar, apart from Charles and myself, was Dan Hannan. But there were many ex-Balliol folk from the area.
Because of pressure of other work I could stay only for the first speaker, but I got a question in at the end of his pitch. This was Professor Gideon Henderson (Oxford Professor of Earth Sciences).
He explained what it was that had first convinced him of the seriousness of global warming. Based on the physics, he realised that without the greenhouse effect, our mean global temperature would be around minus 15 Deg C. The world would be a snowball, frozen down to the equator. And why isn’t it a snowball? The greenhouse effect. Thank you, CO2.
He failed to mention that while CO2 is a greenhouse gas, it is much less important than water vapour (about which we can do nothing, as long as the wind blows over the ocean). And he failed to mention that the greenhouse effect of CO2 is governed by a negative logarithmic equation, a law of diminishing returns, so that while the existing atmospheric CO2 has a significant effect, increases in the current level have a small and diminishing effect.
So to my question (as near as I can remember):
Professor Henderson: You just showed a slide of temperature over the last 600,000 years, showing four previous interglacials. These earlier interglacials look almost exactly like the current one — except that two clearly show a slightly higher peak than today’s temperature. So what exactly is the exceptional event which needs an anthropogenic explanation? Isn’t the current temperature entirely consistent with patterns we have seen for hundreds of thousands of years?
You show a graph of atmospheric CO2, with a sharp rise in recent years from 250 ppm to 400 ppm. Isn’t it the case that if you go back further into earth history, you find long periods when the level was more than ten times higher than today? And weren’t these periods associated with Ice Ages, not warming?
You show Al Gore’s graph, with a striking correlation between temperature and CO2 levels over 600,000 years. Isn’ it the case that if you look at those graphs in higher resolution, you find that the temperature graph leads the CO2 graph by around 800 to 1000 years? And doesn’t this show that temperature drives CO2, not that CO2 drives temperature? We can think of plausible astronomical reasons why temperature might be cyclical, but surely the only reason why CO2 levels might be cyclical is that they follow temperature?
As I concluded, I seemed to notice a sharp intake of breath from the audience.
Of course we who work with ideas, whether scientists or politicians, are accustomed to members of the audience trotting out their favourite “killer question”, seemingly oblivious to the fact that we have heard it many times before. Professor Henderson had his answers ready.
Current warming was faster than previously observed, he said (even though there has been no warming at all for nearly two decades!). He accepted my estimate of CO2 levels ten times higher than today, but insisted that this occurred during the Cretaceous period, and gave rise to the Cretaceous warming. But it is my understanding that these very high CO2 levels obtained for a very long period, during much of which we had Ice Age conditions.
On the Al Gore graph, he presented (rather too glibly, I thought, as though he’d brought an extra slide just against the eventuality of this question) CO2 and temperature data over a relatively short period, which appeared to show that they moved precisely in sync. But he failed to explain why CO2 lagged temperature over the longer period, or what he thought caused the cyclicity of CO2 levels.
As Thomas Huxley observed, the great tragedy of science is the slaying of a beautiful hypothesis with an ugly fact. But I rather enjoy doing it.