Variability of the Earth’s climate - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 79

Figure 2.36. Comparison of R(CO 2 ) and climatic effect of cosmic rays with estimated tropical
sea surface temperature anomalies from proxies during the Phanerozoic (adapted from Shaviv
and Veizer, 2003).
flux remains unclear to this writer. While Figure 2.36 is very supportive of the
argument made by Shaviv and Veizer that cosmic rays are more important than
CO 2 in determining long-term climate change, the basis for this figure seems
murky.
However, as we discussed previously, Royer et al. (2004) presented corrected
estimates of sea surface temperature during the Phanerozoic, due to changes in pH
of the oceans induced by changes in the CO 2 level of the atmosphere and changes
in Ca concentrations and the calcium carbonate saturation state in seawater. With
these changes, the variability of CO 2 was claimed to conform better to paleo-
temperatures, while the cosmic ray record does not. Shaviv and Veizer rebutted
Royer's arguments, and the matter does not seem to be fully resolved.
2.3.10.7 Oxygen in the Phanerozoic atmosphere
It would be overly simplistic to treat the Phanerozoic as if it were an extension of
our current climate, but with variable CO 2 concentration. Continental drift pro-
duced significant changes in the distribution of landmasses on Earth, producing
variable feedback effects in response to changing CO 2 . The Earth's atmosphere
was quite different. Atmospheric O 2 concentration varied considerably over the
Phanerozoic. Oxygen levels reached as high as 30-35% in the so-called Permo-
Carboniferous between about 330 and 270 million years ago. During that period,
''giant insects, including dragonflies reached wing spans up to 80 cm. Along with
dragonflies, there are unusually large amphibians, mayflies, millipedes, hexapods,