Geoscience Reference
In-Depth Information
Figure 2.20. Estimates of CO 2 over the past 65 million years as provided by Doria et al. (2011).
The gray area is modeled using GEOCARB. The colored data points are measured by various
techniques referred to by Doria et al. (2011). Doria et al. measured the vertical green bar. The
vertical red and blue lines are periods of relative warmth and cold.
The connection between CO 2 and climate remains fuzzy to this writer based
on Figure 2.20 .
2.3.8
60 to 40 million years ago
Pearson and Palmer (2000) provided the results shown in Figure 2.21 . There is a
general tendency for higher CO 2 concentrations to be associated with higher T G ,
although a direct one-to-one correspondence is lacking.
Others have determined that CO 2 concentrations were relatively high about 50
million years ago. For example, Lowenstein and Demicco (2006) estimated that
CO 2 1,000-3,000 ppm about 50 million years ago. Pagani et al. (2005) pointed
out that ''the relation between the partial pressure of atmospheric carbon dioxide
(pCO 2 ) and Paleogene climate is poorly resolved.'' They ''used stable carbon
isotopic values of di-unsaturated alkenones extracted from deep-sea cores to
reconstruct pCO 2 from the middle Eocene to the late Oligocene ( 45 to 25
million years ago).'' Their results indicated that pCO 2 ranged between 1,000 to
1,500 ppm in the Middle to Late Eocene, then decreased in several steps during
the Oligocene, and reached modern levels by the latest Oligocene.
Edwards et al. (2010) provided the result shown in Figure 2.22 , which is
similar in some ways to that of Pearson and Palmer (2000) in that the warm
period from 60 to 40 million years ago is associated with generally higher values
of the CO 2 concentration. However, Figure 2.21 shows considerable scatter, and
furthermore, there isn't much variation in CO 2 while temperatures changed con-
siderably over the past 20 million years. These results seem to suggest that on
balance the warmest climates are associated with higher CO 2 concentrations, but
 
Search WWH ::




Custom Search