Australia: The Land Where Time Began

A biography of the Australian continent 

Atmospheric Carbon Dioxide Linked to Climate Change in the Mesozoic and Early Cainozoic

The role of CO₂ in temperature changes during the history of the Earth prior to the Quaternary is not well known (Veizer et al., 2000), but those of the quaternary have been studied more thoroughly.  The occurrence of cool periods during the times of high atmospheric CO₂ levels in the 'greenhouse world' (Royer et al., 2000; Royer, 2006) of the Mesozoic suggested by the range of geological evidence of cool periods of these times, indicated by models (Berner, 2004) and fossil soils (Ekart, 1999) was very difficult to interpret. In this paper the authors¹ present high-resolution records of atmospheric CO₂ concentrations obtained from a combination of carbon isotope analyses of fossil bryophytes (non-vascular plants) and theoretical modelling (Fletcher et al., 2005; Fletcher et al., 2006). It is indicated from these records that atmospheric CO₂ levels rose from about 420 ppmv in the Triassic (about 200 Ma), peaking at about 1,130 ppmv in the Middle Cretaceous (about 100 Ma). After the peak the CO₂ levels declined to about 680 ppmv by 60 Ma. These variations have been shown to coincide with large climate shifts in the Mesozoic(Dromart et al., 2003; Wilson et al., 2002; Shouten et al., 2003) by time-series concentrations, unlike earlier suggestions of climate-CO₂ decoupling during this interval. On several occasions these reconstructed CO₂ concentrations drop below the simulated thresholds for glaciation initiation (DeConto & Pollard, 2003), which therefore helps to explain cold intervals occurring in a greenhouse world (Royer, 2006).

Sources & Further reading

1. Fletcher, Benjamin J., Stuart J. Brentnall, Clive W. Anderson, Robert A. Berner, and David J. Beerling. "Atmospheric Carbon Dioxide Linked with Mesozoic and Early Cenozoic Climate Change." Nature Geosci 1, no. 1 (01//print 2008): 43-48.