Geoscience Reference
In-Depth Information
''Proxy data and box modeling demonstrate that pCO
2
has oscillated over
the Phanerozoic due to changing rates of mantle degassing, weathering, organic
carbon burial and carbonate turnover. The simulated changes in pCO
2
correspond roughly to paleoclimatic reconstructions supporting the view that
Phanerozoic climate change has been driven mainly by changes in atmospheric
pCO
2
. A different picture emerges from the evaluation of
d
18
O values in marine
carbonate fossils. These data show regular oscillations with a shorter period
indicating changes in surface temperatures at low latitudes that are consistent
with some paleoclimatic reconstructions but not with surface temperatures
derived from pCO
2
modeling. This difference may be regarded as evidence for
the decoupling of pCO
2
and climate evolution. The latter view is supported by
recent modeling of galactic cosmic radiation over the last billion years. These
new data show a surprisingly strong correlation with
d
18
O-based temperature
reconstructions suggesting that climate change has been driven mainly by cosmic
radiation. Nevertheless, temperatures calculated from the marine
d
18
O record are
met with skepticism because the extremely low Jurassic surface temperatures
derived from this proxy are not consistent with other observations.''
Wallmann (2004) provided the estimate of
the average global
surface
temperature shown in
Figure 2.26
.
Several Internet sites claim that Veizer et al. (2000) updated their global
average Phanerozoic temperatures based on oxygen isotope data online in 2004 at:
However, that website is defunct. Nevertheless, Ziegler presented a graph that is
claimed to be this update at:
Figure 2.26. Estimate of average global temperature during the Phanerozoic (adapted from
Wallmann, 2004).
Search WWH ::
Custom Search