Variability of the Earth’s climate - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 77

Breeker et al. (2010) developed yet another estimate of paleo-CO 2
concentrations over the past 400 million years. They also concluded that there is a
coupling of CO 2 and temperature.
It is interesting that since 2004 each successive published paper purports to
find a tighter relationship between CO 2 and temperature in the Phanerozoic, yet
the data have not changed much. One possibility is that there really is such a
correlation and better analyses have uncovered this. An alternate hypothesis is
that only by emphasizing the role of CO 2 in climate change can one obtain
research funding in the 21st century. As a result, increasingly more bias creeps
into published papers as investigators seek to ingratiate themselves with ortho-
doxy. In all cases, the data are sparse, noisy, and dicult to interpret. It remains
dicult to resolve the degree to which these two alternatives are involved.

2.3.10.5 Climate sensitivity assuming ''The Force'' is with CO 2
Perhaps the most pervasive issue in modern climatology is the question of how
much global warming ( D T) in the 21st century would result from a doubling of
the CO 2 concentration from the pre-industrial level of 280 ppm. While many
estimates have been made, the canonical value often used is 3 C. Like the
porridge in The Three Bears, this value is just right—not so great as to lack
credibility and not so small as to seem benign. Unfortunately, all of the estimates
made to date by various procedures lack adequate data and involve considerable
speculation.
Assuming that variations in CO 2 concentration were the major cause of all
historical climate change (which seems to be a widespread belief amongst paleo-
climatologists) one can attempt to quantitatively estimate the relationship between
changing CO 2 and global average temperature from the data. Unfortunately, most
of the data are noisy and uncertain. According to Figures 2.25 to 2.27 , the global
average temperature dropped by roughly 11 C prior to the great glaciation around
300 million years ago, while R(CO 2 ) dropped from roughly 16 to 1. A factor of 16
represents four doublings. Hence, one might conclude that going backward in time
from 300 million years ago, each doubling of CO 2 produced a temperature rise of
11/4 ¼ 2.8 C. However, the glacial period at 445 million years ago would involve
infinite climate sensitivity since CO 2 did not appear to vary much during that
glacial period.
Royer et al. (2007) provided another estimate of climate sensitivity by fitting
proxy data to a geological model for CO 2 during the Phanerozoic. Unfortunately,
the data are sparse, noisy, and somewhat unreliable. Nevertheless, Royer et al.
(2007) concluded that D T G is greater than 1.5 C and the best fit for the effect of
doubling CO 2 is D T G 2.8 C.

2.3.10.6 Correlation with galactic cosmic rays

Veizer et al. (2000) presented

'' ... a reconstruction of tropical sea surface temperatures throughout the