Variability of the Earth’s climate - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 62

atmosphere that maintained high pCO 2 levels and warm climate until the
decarbonation factory waned with the collision of Greater India with Asia at
50Ma, closely coinciding with the Early Eocene climatic optimum. At about
this time, the India continent and the highly weatherable Deccan Traps drifted
into the equatorial humid belt where uptake of CO 2 by silicate weathering further
perturbed the equilibrium towards progressively lower pCO 2 levels and a cooling
trend that eventually triggered the expansion of Antarctic ice sheets in the earliest
Oligocene, even if global seafloor production rates remained steady.''

This conclusion appears to be based on the supposition that climate is
controlled by CO 2 and, for any time period in which climate changed, a geological
model for a change in CO 2 must be developed to explain why the climate changed.
The arguments in this study seem plausible, but it does not appear to this writer
as clear-cut as Kent and Muttoni (2008) seem to think.
Cui et al. (2011) discussed the transient global-warming event known as the
Paleocene-Eocene Thermal Maximum that occurred about 55.9 million years ago.
''The warming was accompanied by a rapid shift in the isotopic signature of
sedimentary carbonates, suggesting that the event was triggered by a massive
release of carbon to the ocean-atmosphere system.'' They said that ''the source,
rate of emission and total amount of carbon involved remain poorly constrained.''
They used ''an expanded marine sedimentary section from Spitsbergen to recon-
struct the carbon isotope excursion as recorded in marine organic matter [and
found that] the total magnitude of the carbon isotope excursion in the ocean-
atmosphere system was about 4 .'' They used a climate model to infer that the

peak rate of carbon addition was slower than the present rate of carbon emissions,
although emissions were extended over a longer period.
Ruddiman (2010) wrote a ''Perspective'' article in Science entitled ''A
paleoclimatic enigma''. In this paper, he emphasized that the Earth's climate had
been cooling from pole to pole for 50 million years prior to the onset of
alternating ice ages and interglacials about 2.7 million years ago. During this 50-
million-year period:

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''Arctic forests changed from frost-intolerant evergreens to temperate
deciduous trees to cold-adapted spruce and larch and eventually to tundra.
Antarctica was mostly ice-free until 34 million years ago; glaciers of varying size
then existed on the continent until 14 million years ago, after which a large and
relatively stable ice sheet formed. The gradual shift toward heavier d 18 O values in
CaCO 3 shells of sea-floor foraminifera since 50 million years ago documents a
combined deep-ocean cooling and increase in Antarctic ice.'' [See Figure 2.23 ].

Ruddiman (2010) went on to say:

''Until a decade ago, most paleoclimate modelers attributed this ongoing
bipolar cooling to a gradual reduction in the CO 2 concentration in the atmo-
sphere. This inferred CO 2 decrease was ascribed to a combination of reduced