Detailed Response to Royer et al.’s letter “CO2 as a primary driver of Phanerozoic Climate”

Royer et al. (2004) introduce a seawater pH correction to the Phanerozoic temperature reconstruction based on δO variations in marine fossils. Although this correction is a novel idea and it is likely to have played some role in offsetting the δO record, we show that (a) The correction cannot be as large as claimed by Royer et al. (b) Irrespective of the size of the correction, a CO2 signature cannot possibly be seen in the data. (c) Even though the CO2 signature cannot be seen, the pH correction implies only a somewhat higher global temperature sensitivity than that in Shaviv and Veizer (2003), a sensitivity that is consistent with a “black body Earth”, but only marginally with the lower limit of the IPCC range.