Radiation Transfer Calculations and Assessment of Global Warming by CO₂

We present detailed line-by-line radiation transfer calculations, which were performed under different atmospheric conditions for the most important greenhouse gases water vapor, carbon dioxide, methane, and ozone. Particularly cloud effects, surface temperature variations, and humidity changes as well as molecular lineshape effects are investigated to examine their specific influence on some basic climatologic parameters like the radiative forcing, the long wave absorptivity, and back-radiation as a function of an increasing CO 2 concentration in the atmosphere. These calculations are used to assess the CO 2 global warming by means of an advanced two-layer climate model and to disclose some larger discrepancies in calculating the climate sensitivity. Including solar and cloud effects as well as all relevant feedback processes our simulations give an equilibrium climate sensitivity of CS = 0.7°C (temperature increase at doubled CO 2 ) and a solar sensitivity of SS = 0.17°C (at 0.1% increase of the total solar irradiance). Then CO 2 contributes 40% and the Sun 60% to global warming over the last century.