Greenhouse effect dependence on atmospheric concentrations of greenhouse substances and the nature of climate stability on Earth

Due to the exponential positive feedback between sea surface temperature and saturated water vapour concentration, dependence of the planetary greenhouse e ect on atmospheric water content is critical for stability of a climate with extensive liquid hydrosphere. 5 In this paper on the basis of the law of energy conservation we develop a simple physically transparent approach to description of radiative transfer in an atmosphere containing greenhouse substances. It is shown that the analytical solution of the equation thus derived coincides with the exact solution of the well-known radiative transfer equation to the accuracy of 20% for all values of atmospheric optical depth. The de10 rived equation makes it possible to easily take into account the non-radiative thermal fluxes (convection and latent heat) and obtain an analytical dependence of the greenhouse e ect on atmospheric concentrations of a set of greenhouse substances with arbitrary absorption intervals. The established dependence is used to analyse stability of the modern climate of 15 Earth. It is shown that the modern value of global mean surface temperature, which corresponds to the liquid state of the terrestrial hydrosphere, is physically unstable. The observed stability of modern climate over geological timescales is therefore likely to be due to dynamic singularities in the physical temperature-dependent behaviour of the greenhouse e ect. We hypothesise that such singularities may appear due 20 to controlling functioning of the natural global biota and discuss major arguments in support of this conclusion.