Variability of the Earth’s climate - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 54

entire globe ( D T G ).'' In a personal communication to this writer, van de Wal
indicated that

5 ðD T G Þ . Evidently, some of the data were discounted,
and the very wide scatter was not considered an impediment to drawing
conclusions. The final result is the black line in Figure 2.1 4 . This line passes
through ðD T NH Þ¼ 0 at 300 ppm CO 2 and has slope 0.125 C/ppm. Thus, in going
from a pre-industrial

ðD T NH Þ 2 :

level of 280 ppm to the present level of 395 ppm, van

125 ¼ 14.4 C and

de Wal et al. (2011) would predict that ðD T NH Þ 115 0 :

5 ¼ 5.8 C. There are three possibilities: (i) one possibility is that if
we hold CO 2 at 395 ppm and wait long enough ðD T G Þ will approach 5.8 C; (ii) the
second possibility is that the climate is determined by factors other than CO 2 ;
(iii) the third possibility is that the results of van de Wal et al. (2011) are inaccu-
rate. This writer leans to the second and third possibilities. It seems likely that the
variation of CO 2 and T G over the past 20 million years has not been pinned down
very accurately but, even if it has, the putative slope of the black line i n Figur e
2.1 4 assumes that CO 2 is the sole determinant of climate change. Yet, the vari-
ability of CO 2 over the past 20 million years was moderate, and attributing all
climate changes over that period to CO 2 leads to a severe overestimate of the
importance of CO 2 . It seems likely that there are more things than CO 2 in heaven
and earth than are dreamt of in the philosophy of paleoclimatologists.
Foster et al. (2009) showed that while the period from 25 to 5 million
years ago was ''a period of relative warmth'' and only Antarctica was glaciated,
''paradoxically'' CO 2 concentrations were comparable with ''pre-industrial values
or even lower.'' ''Records of ice rafted debris and the oxygen isotope composition
of benthic foraminifera suggest that at several times over the last 25 million years
substantial amounts of continental ice did build up in the Northern Hemisphere
but none of these led to sustained glaciation.'' Foster et al. (2009) pointed out
that the ''accepted paradigm'' 5 requires CO 2 to vary in unison with global
temperature. However, they emphasized: ''Reconstructing the concentration of
atmospheric CO 2 beyond the reach of the Quaternary ice cores is, however, a
notoriously dicult task. Nonetheless there is a growing consensus that pCO 2 did
decline over the Cenozoic, but not exactly sympathetically with climate as the
paradigm suggests'' (see Figure 2.1 6 ). They also said: ''This is likely because the
pCO 2 records are not perfect and other phenomena such as ocean circulation,
continental configuration, and surface albedo (vegetation and ice coverage) also
influence climate.'' They suggested that other geological factors could change the
threshold for NH glaciation to occur. One such factor is uplift of the North
American Cordillera that

ðD T G Þ 14 : 4 = 2 :

''would have resulted in significant cooling of the

Northern North American Continent . This suggests uplift of the North Amer-

ican Cordillera in the Late Miocene may have played an important role in priming
the climate for the intensification of Northern Hemisphere glaciation in the Late
Pliocene.''

...

5 The ''accepted paradigm'' is an almost religious belief that only CO 2 concentrations control
climate change, and paleoclimatologists often interpret data and models with considerable bias
toward that belief.