A model study of the greenhouse effects due to increasing atmospheric CH4, N2O, CF2Cl2, and CFCl3

Abstract

Study of the greenhouse effects of increasing atmospheric trace gases has so far relied mainly on the use of one‐dimensional models, especially the radiative‐convective models (cf. World Meteorological Organization, 1982; National Research Council, 1983). Here we use the two‐dimensional (altitude‐latitude) radiative‐dynamical model of Wang et al. (1984) to investigate the effects on vertical and meridional temperatures of increases of atmospheric methane, nitrous oxide, and chlorofluorocarbons. The model, consisting of a high‐latitude zone and a low‐latitude zone, couples the meridional and vertical temperature structure through energy balance between radiative flux and vertical and meridional heat transports. First, we show that the thermal radiation flux perturbations, i.e., the driving force for the subsequent climate change, caused by increases of these trace gases and carbon dioxide, are different in nature. Next, a comparison of model‐calculated present climate and climate change between the one‐dimensional and two‐dimensional models is performed. The results indicate that the two‐dimensional model simulates much more realistic temperature and humidity distributions. For a doubling of the atmospheric CO2 concentration of 330 parts per million by volume, the two‐dimensional model computes a global surface warming of 3.7 K with larger high‐latitude amplification, which is in good agreement with results obtained from general circulation models. For the study of the surface warming due to increases of trace gases, it is found that the one‐dimensional model using a 6.5 K km−1 critical lapse rate for convective adjustment appears to calculate a much larger surface warming than the two‐dimensional model. On the other hand, the one‐dimensional model using the moist adiabatic critical lapse rate, although it can not simulate adequately the present tropospheric temperature structure, calculates surface warming effects in close agreement with those of two‐dimensional model results. We have used the two‐dimensional model to estimate on the time scale of decades the potential greenhouse effects due to increases of these gases. Although the calculations depend largely on the adopted scenarios for future increases, the results nevertheless reveal that the trace gases could potentially augment the surface warming due to carbon dioxide increase by more than 60%.