This figures shows estimates of the changes in
carbon dioxide concentrations during the
Phanerozoic. Three estimates are based on
GEOCARB III (Berner and Kothavala 2001), Carbon-Oxygen-Phosphorus-Sulfur-Evolution COPSE (Bergmann et al. 2004) and Rothman (2001). These are compared to the carbon dioxide measurement database of Royer et al. (2004) and a 30
Myrfiltered average of those data.
Error envelopes are shown when they were available. The right hand scale shows the ratio of these measurements to the estimated average for the last several million years (the
Quaternary). Customary labels for the periods of
geologic time appear at the bottom.
Direct determination of past carbon dioxide levels relies primarily on the interpretation of
carbon isotopic ratios in fossilized soils (
paleosols) or the shells of
phytoplankton and through interpretation of
stomatal density in fossil plants. Each of these is subject to substantial systematic uncertainty.
Estimates of carbon dioxide changes through geochemical modeling instead rely on quantifying the geological sources and sinks for carbon dioxide over long time scales particularly:
carbonate deposition. As such, these models are largely independent of direct measurements of carbon dioxide.
Both measurements and models show considerable uncertainty and variation; however, all point to carbon dioxide levels in the past that have been signifcantly higher than they are at present. While the GEOCARB Carbon dioxide levels in the most part of the Phanerzoic Eon shows a fit and resulting climate sensitivity similar to todays values, the early Phanerozoic includes a global ice age during the Ordovician age combined with high atmospheric carbon contents based on the same project. There have been different speculations about the reasons but no acknowledged mechanism so far.
This figure was prepared by
Robert A. Rohde from published data and is incorporated into the Global Warming Art project.
Veizer, J., Godderis, Y. & Francois. L.M., Evidence for decoupling of atmospheric CO2 and global climate during the Phanerozoic eon. Nature 408, 698-701 (2000) 
Nir J. Shaviv, Ján Veizer: Celestial driver of Phanerozoic climate?, Geological Society of America Vol. 13, Issue 7 (Juliy 2003), S. 4–10, Online (pdf 454 KByte)
All data except GEOCARB III appear on the 2004 geologic time scale (Gradstein et al. 2005). GEOCARB III appears on the Gradstein & Ogg (1996) time scale.
All models are reported in terms of the ratio of past CO2 concentrations to "present" CO2 concentrations, where "present" represents some average value for the last few million years. To compare to direct measurements a value of 260 ppmv is chosen for the recent period, with an uncertainty of 10-15%.
No models are capable of resolving changes faster than ~10 Myr.
Measurements based on the interpretation of paleosols sometimes result in apparent CO2 concentrations < 0 ppmv. These were set to 0 ppmv.
Different measurements in the Royer et al. compilation come from different authors and involve different techniques. As such the error bars are not necessarily comparable. For example, some sources may have included only statistical measurement error, whereas others may have included statistical and systematic errors. Other measurements report no uncertainty at all. Because of these factors, the error measurements were ignored when determining the 30 Myr measurement average.