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 CO 2 and concentration in the atmosphere, i.e., ΔRF = 5.35ln(C/C o ). It is an approximation because water vapour competes unevenly with CO 2 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 CO 2 , 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.