Figure 6 A schematic reconstruction (solid line) of mean global surface temperature through the last 100 million years, based on analyses of various marine and terrestrial deposits. The dashed-line extension is a prediction of future trends through the coming 400 years, based on the assumption of substantial utilization of the fossil fuel reservoir. The vertical line shows the approximate range of surface temperature in climate model predictions for a doubling of CO2 levels, at about 100 years in the future. Modified from T. J. Crowley, Journal of Climate, vol 3, pp 1282-1292, 1990.