Interactive comment on CO2 radiative forcing during the Holocene Thermal Maximum revealed by stomatal frequency of Iberian oak leaves (2)

Abstract

Here we analyse radiocarbon-dated Quercus leaf assemblages from northern Spain to obtain past atmospheric CO2 mixing ratios for the time period 9000–1100 cal BP by means of stomatal frequency analysis. Normalized, stomata based CO2 records show fluctuations of 20 ppmv during the Holocene that parallel Northern 5 Hemisphere palaeotemperature reconstructions. The calculated radiative forcing of CO2 indicates a CO2 contribution of +0.1_C to the Holocene Thermal Maximum from 7 to 5 kyr BP, and −0.05_C to the Neoglacial cooling around 4 kyr BP. Derived northern hemispheric air-temperature anomalies forced by atmospheric CO2 variation suggest an active role 10 of this trace gas as an amplifier of initial orbital forcing of Holocene climate