Variability of the Earth’s climate - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 56

Figure 2.17. Estimated CO 2 vs. temperature over 20 million years (adapted from Tripati et al.,
2009).

during major glacial transitions of the past 20myr, supporting the hypothesis

that greenhouse gas forcing was an important modulator of climate over this
interval via direct and indirect effects.''

...

However, they also said:

''During the Middle Miocene, when temperatures were 3 to 6 C warmer
and sea level was 25 to 40 meters higher than at present, pCO 2 appears to have
been similar to modern levels.''

One is left with this inference. Assuming the results of Tripati are accurate,
there appears to be a general tendency for pCO 2 to be higher during warmer
periods but, as Foster et al. (2009) said, the variation is ''not exactly sym-
pathetically with climate as the paradigm suggests.'' Nevertheless, as before, one is
left with three possible interpretations similar to those reached in regard to van de
Wal et al. (2011): (i) one possibility is that if we hold CO 2 at 395 ppm and wait
long enough, D T G will approach 3 to 6 C; (ii) the second possibility is that climate
is determined by factors other than CO 2 ; (iii) the third possibility is that the
results of Tripati et al. (2009) are inaccurate. This writer leans toward the second
and third possibilities.