I I I I I I M I I I I

FIGURE 9.1 5 Reconstructions of mean annual temperature and annual precipitation at Les Echets, (left) and La Grande Pile, France (right) (for locations, see Fig. 9.17).Values are expressed as deviations from modern values (9.5 °C and 1080 mm at La Grande Pile, and 11 °C and 800 mm at Les Echets). Error bars are computed by Monte Carlo simulation.The chronology is approximate before the Upper Pleniglacial, being dated by correlation with the SPECMAP marine isotope record, shown on the right (cf. Section 6.3.3) (Guiot et al., 1989). Compare this with Fig. 9.19.

compared with observed data. This is both a test of the model's ability to simulate the paleoclimate correctly, and of the accuracy with which the response surfaces can reproduce climatic conditions. The results (for eastern North America) showed good broad-scale agreement between observed and simulated pollen distributions, though late glacial conditions were less reliably simulated, presumably reflecting the difficult problems of finding appropriate analogs in the modern data network. More recently, T. Webb et al have directly compared January and July paleotemperatures, and annual precipitation, derived from response surfaces ("inferred") with paleocli-matic reconstructions "simulated" by CCM1 (Webb et al, 1993b, 1997) (Fig. 9.16). The results show good agreement for the Holocene time slices between these quite independent approaches (Fig. 9.16e); differences in July paleotemperature recon-

Inferred from Pollen

Inferred from Pollen

Difference between Simulated and Modem Observed (5-A/fO)

Difference between Inferred and Simulated (/-S)

Difference between Inferred and Simulated (/-S)

FIGURE 9.16 January mean temperatures (°C) at 3 ka intervals: (upper panel) reconstructed from pollen by the use of response surfaces and (second panel) these values expressed as departures from modern conditions; (third panel) temperatures simulated by the NCAR general circulation model (CCMI ) and (fourth panel) those values expressed as differences from modern conditions.The lowermost panel shows differences between the pollen-based reconstructions and those of the model (first and third panels) (Webb et ai, 1993b).

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