Figure 3.

Crossplots of atmospheric CO₂ and global surface temperature against pollen morphospecies richness. (a,b) Standardized scores (identical to data in figure 2). Bars represent standard errors of the mean (both for x-axis and y-axis; many are smaller than the symbols). (c,d) Standardized first-difference scores. First differences are computed from the data in figure 1, then transformed to a z distribution (series mean = 0 and s.d. = 1). Type II regressions and their associated p-values are plotted in all panels; companion r² values come from a bootstrap approach (see also table 1).