Climate modes through the Phanerozoic based on paleoclimatic analysis (Frakes et al., 1992) and oxygen isotopic evolution of the ocean (Shaviv and Veizer, 2003; Royer et al., 2004). Climate modes: C = cool; W = warm (see definitions in Frakes et al., 1992). Top panel: Temperature curves represent present global average minus the reconstructed temperatures: the modern global average temperature in the geologic record would have a value of zero (see Royer et al., 2004 for details). The three temperature curves are: (1) an uncorrected curve (Veizer et al., 1999) [solid line], (2) a pH-adjusted curve based on modeled CO2, and (3) pH-adjusted proxy CO2 data (Royer et al., 2004) [dashed and gray line respectively]. The horizontal dashed line is based on the Paleogene glaciation in the Cenozoic (Zachos et al., 2001), which would give a temperature of ca. +2.2 °C above the present global average. If this horizontal dashed line is used as an estimate for warm (above) and cool (below) climates, then correspondence with the climate modes of Frakes et al. (1992) is much better. Ψ = Ediacaran; ε = Cambrian; O = Ordovician; S = Silurian; D = Devonian; C = Carboniferous; P = Permian; = Triassic; J = Jurassic; K = Cretaceous; Pg = Paleogene; N = Neogene. Bottom panel: Phanerozoic atmospheric CO2 concentrations based on the GEOCARB III model (dashed line) and proxy CO2 data (solid grey line) after Royer et al., 2004.
It is beyond the scope of this entry to discuss all the periods in
the geologic record; however, a summary of warm climate modes will
be provided with appropriate references for further study (Figure
Figure G53 depicts the climate modes of the Phanerozoic as
determined through paleoclimatic analysis (Frakes et al., 1992 )
and oxygen isotopic evolution of the ocean (Veizer et al., 1999 ;
Shaviv and Veizer, 2003 ; Royer et al., 2004 ).
What is apparent in Figure G53 is a lack of co-variation between
reconstructed and modeled atmospheric CO 2 levels with
warm and cool climate modes; such a finding was reported by Shaviv
and Veizer ( 2003 ), and vehemently debated by Royer et al.
An isotope curve indicates that by the Middle–Late Cambrian,
paleotemperatures far exceeded present temperatures (Figure G53 ),
which coincided with extremely high atmospheric CO 2
levels at that time (Royer et al., 2004 ), possibly as a result of
intense volcanism over the Precambrian–Cambrian transition (Doblas
et al., 2002 ).
After the Late Ordovician glaciation, the Late Silurian still
experienced relatively cool temperatures, although by the beginning
of the Devonian, temperatures begin to rise sharply, reaching a
peak in the Middle Devonian before decreasing again (Figure G53 ).
Paleotemperatures rose sharply during this interval, from cool to
warm, but peaked during the Early Triassic (Figure G53 ).
However, this is not apparent in Figure G53 .
Four major greenhouse (warm) modes have been identified in the
Phanerozoic (Figure G53 ), and within these intervals, several (or
many) transient climate events conducive with rapid, extreme
warming can be identified.
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