EXAMPLE CALCULATION OF CRITICAL LIMITS FOR GREENHOUSE GAS CONTENT IN THE ATMOSPHERE USING A MINIMAL SIMULATION MODEL OF THE GREENHOUSE EFFECT

Abstract

A minimal horizontally homogeneous simulation model of the atmosphere allowing calculation of the Earth's radiative budget components is proposed in this paper. The atmosphere is modeled as a set of horizontal layers with different geometric thicknesses but equal optical properties. The model has three parameters characterizing the ability of the layer to reflect and absorb short-wave radiation, as well as to absorb longwave radiation. These parameters were chosen so as to ensure the maximum possible similarity of the model radiative budget to that adopted by the Intergovernmental Panel on Climate Change (IPCC) in its Third Assessment Report (TAR). This provided a satisfactory degree of similarity. The model allowed us to obtain a linear approximation of the relationship between surface layer temperature and atmospheric content of three greenhouse gases (carbon dioxide CO2, methane CH4, and nitrous oxide N2O). Example calculations based on the assumption that the critical threshold for the present temperature increase is equal to 3°C yielded the following limit for the long-term levels of the greenhouse gas concentration (as was mentioned in the TAR, such long-term warning leads to disruption of the Greenland ice sheet) ΔcCO2/300 + ΔCCH4/10 + ΔCN2O/1.5 ≤ 1. Here, Δc is change in concentration relative to the present level (in ppm),.