Introduction

The Cretaceous period (140–65 Ma) is generally considered to represent the Earth in an extreme ‘greenhouse’ mode (Frakes et al., 1992), most obviously manifested in the plant fossil record by the high latitude occurrence of substantial polar forests. Increased global warmth is thought to have been derived, in part, from the configuration of the continents (Barron & Washington, 1985), allowing significant poleward heat transport (Herman & Spicer, 1996), and also from the high partial pressure of atmospheric CO2 (Berner, 1994). The mid-Cretaceous in particular has received considerable research attention as a period for evaluating the extent to which it provides a possible analogue for a greenhouse Earth warmed by a high atmospheric CO2 content (Barron, 1982, 1983; Barron et al., 1993, 1995; Price et al., 1995, 1997, 1998). It is unlikely, however, that the mid-Cretaceous greenhouse world, or indeed any other period in Earth history, represents a robust analogy for a future globally-warmed Earth, because of the large number of differences between the past and now, particularly geography, orography and oceanic boundary conditions (Crowley, 1990, 1993; Barron, 1994). Nevertheless, this suggestion has not been addressed for vegetation and the terrestrial carbon cycle. Therefore the future relevance of the most geologically recent episode of extreme ‘greenhouse’ warmth in the mid-Eocene is explored in further detail in Chapter 8.