Variability of the Earth’s climate - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 78

Figure 2.35. Comparison of estimates of CO 2 history with tropical sea temperature in the
Phanerozoic (adapted from Veizer et al., 2000).
Phanerozoic eon from [their] database of oxygen isotopes in calcite and aragonite
shells. The data indicated large oscillations of tropical sea surface temperatures in
phase with the cold and warm cycles, thus favoring the idea of climate variability
as a global phenomenon.''
But their data were not in consonance with reconstructed atmospheric carbon
dioxide concentrations. They concluded: ''The results can be reconciled if atmo-
spheric carbon dioxide concentrations were not the principal driver of climate
variability on geological timescales for at least one-third of the Phanerozoic eon,
or if the reconstructed carbon dioxide concentrations are not reliable'' (see Figure
2.35 ).
Shaviv and Veizer (2003) analyzed the ''reconstructed seawater paleo-
temperature record for the Phanerozoic and compared it with the variable cosmic
ray flux (CRF) reaching Earth'' as well as ''the reconstructed partial pressure of
atmospheric CO 2 (pCO 2 ).'' They found ''that at least 66% of the variance in the
paleotemperature trend could be attributed to CRF variations, likely due to solar
system passages through the spiral arms of the galaxy. Assuming that the entire
residual variance in temperature is due solely to the CO 2 greenhouse effect, [they
proposed] a tentative upper limit to the long-term 'equilibrium' warming effect of
CO 2 , one which is potentially lower than that based on general circulation
models.'' They used Berner's estimates for p(CO 2 ), and d 18 O values of calcitic
shells to estimate proxy-based paleo tropical sea surface temperatures. Cosmic ray
activity indicators were based on 10 Be and 14 C isotopes. The results of Shaviv and
Veizer (2003) are shown in Figure 2.35 . Paleo sea surface temperature anomalies
were taken from estimates based on oxygen isotope proxies. The process by which
Shaviv and Veizer arrived at temperature anomalies from variations in cosmic ray