…Some fish, some barrel

By Gareth Renowden 29/10/2009


I’m afraid he’s at it again. Wishart, that is. It seems he can’t stop himself from reading Hot Topic and then posting his reactions. In his latest excursion, he reads a comment of mine, and then feels the need to once again demonstrate the depth of his understanding. He begins thus:

Can you believe the chutzpah? The thing that gets me about climate Chicken Littles is the way they repeat bogus claims ad nauseum as if true… this comment from Gareth Renowden at Hot Topic tonight illustrates ignorance on this point:

“In deep time, there have been periods when CO2 has been higher than now (how much higher is a matter of study), but lots of CO2 is inevitably associated with a warmer planet.”

Invariably?? The blue line is temperature, the black line is CO2:

And he whips out the chart you see above (click on the thumbnail to be taken to the source). It features (without credit to source) on page 34 of Air Con. He continues:

I defy anyone, including Renowden, to find a pattern in the historical record that proves CO2 is “invariably” associated with a warmer planet. It will be especially hard for him as the ice cores all show CO2 rise lags temperature increase by several hundred years, not precedes it.

I didn’t have to try very hard to defy Wishart, because the “pattern” is well-established in the literature:

A pervasive, tight correlation between CO2 and temperature is found both at coarse (10 my timescales) and fine resolutions up to the temporal limits of the data set (million-year timescales), indicating that CO2, operating in combination with many other factors such as solar luminosity and paleogeography, has imparted strong control over global temperatures for much of the Phanerozoic.

That comes from the abstract of Dana Royer’s 2005 paper, CO2-forced climate thresholds during the Phanerozoic (PDF). The paper’s worth a read if you want to understand some of the complexities of deep time and climate, but John Cook at Skeptical Science provides an overview here. Royer’s paper was published well before Air Con, so one has to wonder how it managed to escape Wishart’s attention…

The graph that Wishart relies on comes from this page at a site notable for its sceptic stance, and has been widely used around the crank sites — including microWatts. It appears to be a mash-up of a CO2 data series (there are several — there’s a better graph here; note there’s one reconstruction that doesn’t suggest high CO2 levels 500 mYa), with a schematic of temperature from this site — the rather interesting Paleomap Project. Note that the temperature schematic has been rotated through 90º, re-scaled and re-drawn to fit over the CO2 graph. It’s reminiscent of the sort of graphical jiggery pokery practised by Monckton… But it’s good enough for Wishart, who devotes several pages to over-interpreting the ups and downs of the lines in chapter three of Air Con (pps 34-36).

What happens if you do the exercise properly? Refer to the Royer paper. It doesn’t have the pretty colours, or one single equivalent graph, but it does have a properly nuanced discussion of the relationship between CO2 and temperature over the last 540 million years:

…given the variety of factors that can influence global temperatures, it is striking that such a consistent pattern between CO2 and temperature emerges for many intervals of the Phanerozoic.

A good enough pattern for me.

Wishart also mentions the so-called “lag” between CO2 increases and temperature increases during ice age terminations, as if this somehow changes the radiation physics of CO2. He appears unable to understand that the gas can be both feedback and forcing. During ice age terminations, it’s a feedback to orbital changes that becomes a forcing. Today, it’s a forcing – and we’re doing it. More at Skeptical Science.