Calculation of Atmospheric Radiative Forcing (Warming Effect) of Carbon Dioxide at Any Concentration

Abstract

The Beer-Lambert law does not apply strictly to the relationship between radiative forcing (RF) of CO2 and concentration in the atmosphere, i.e., ΔRF = 5.35ln(C/Co). It is an approximation because water vapour competes unevenly with CO2 over the IR absorption wavelength range. We propose a quadratic model as an improved approximation. It links concentration to RF thereby allowing RF calculation at any concentration, not just ΔRF. For example, at 378 ppmv of CO2, the level in 2005, it calculates RF = 8.67 W m−2, or approximately 2.7% of the total RF of all the greenhouse gases. A second and independent method based on worldwide hourly measurements of atmospheric temperature and relative humidity confirms this percentage. Each method shows that, on average, water vapour contributes approximately 96% of current greenhouse gas warming. Thus, the factors controlling the amount of water vapour in the air also control the earth's temperature.