A MODEL STUDY OF ATMOSPHERIC TEMPERATURES AND THE CONCENTRATIONS OF OZONE, HYDROXYL, AND SOME OTHER PHOTOCHEMICALLY ACTIVE GASES DURING THE GLACIAL, THE PREINDUSTRIAL HOLOCENE AND THE PRESENT

Analysis of air trapped in ice cores shows that the atmospheric contents of the greenhouse gases CO2, CH4 and N2O have increased from the glacial to the pre-industrial holocene. Further increases have been occurring during the industrial era. This may well have contributed to the observed global warming. In addition, CH4 and N2O play large roles in ozone and hydroxyl chemistry. Here we present a model analysis of the changes in atmospheric temperatures and the concentration of O3, OH and related gases between the three epochs. Surprisingly, despite large changes in the atmospheric contents of CO2, CH4 and N2O, total ozone and tropospheric OH hardly changed between the glacial and pre-industrial holocene. The global annual atmospheric CH4 sink increased from 90 to 210 Tg (10(12) g) between the glacial and pre-industrial and since then to 510 Tg, largely following the changes in atmospheric concentrations. The corresponding figures for N2O are 7.8, 11.6 and 13.3 Tg. Our results indicate less than half as much CH4 production from tropical wetlands during the ice age than during the holocene.