At the last glacial maximum when CO2 and precipitation was much lower, the number of trees would have only been 5 % to 10 % of these numbers. (wattsupwiththat.com)
I also agree that its hard to understand how people can claim to derive accurate sensitivity estimates for the last glacial maximum for example, given the large uncertainties. (climateaudit.org)
Black carbon concentrations and fluxes since the Last Glacial Maximum in Greenland and Antarctic ice cores. (usap-dc.org)