Radiative‐photochemical modeling of the annually averaged composition and temperature of the global atmosphere during the last glacial and interglacial periods

Abstract

Recent measurements of CO2, CH4, and N2O content in Antarctic and Greenland ice core air allow the use of an one‐dimensional radiative‐photochemical model to reconstruct the annual global mean vertical distributions of trace gas concentrations for four periods: the contemporary period of 1985, the preindustrial period of 1850, the last glacial period of 18 ka B. P., and the interglacial period before the latter of 120–130 ka B. P. In this model reconstruction, the changes in surface air temperature and tropospheric relative humidity are prescribed, and both dry adiabatic and moist adiabatic lapse rates are used together with several other external estimates of radiative and photochemical parameters for these periods. The considerable reduction of greenhouse gas content in the atmosphere of both glacial and interglacial periods, including about a 50% reduction of stratospheric moisture in the glacial, leads to the warming of the middle and upper stratosphere by about 11 K and 4 K, in the glacial and interglacial periods, respectively. Stratospheric composition is found to be little sensitive to possible large variations of CO and NOx surface sources. The ozone mixing ratio drops to 10–12 ppbv in the lower troposphere and increases to a maximum 6.0–7.5 ppmv in 40 to 46‐km layer, but remains almost the same as in preindustrial and in 1985 periods in the 20 to 30‐km layer. This results in the approximate conservation of total ozone for all four periods considered.