The potency of carbon dioxide (CO2) as a greenhouse gas

By Antero Ollila
September 2014

According to this study the commonly applied radiative forcing (RF) value of 3.7 Wm-2 for CO2 concentration of 560 ppm includes water feedback. The same value without water feedback is 2.16 Wm-2 which is 41.6 % smaller. Spectral analyses show that the contribution of CO2 in the greenhouse (GH) phenomenon is about 11 % and water’s strength in the present climate in comparison to CO2 is 15.2. The author has analyzed the value of the climate sensitivity (CS) and the climate sensitivity parameter () using three different calculation bases. These methods include energy balance calculations, infrared radiation absorption in the atmosphere, and the changes in outgoing longwave radiation at the top of the atmosphere. According to the analyzed results, the equilibrium CS (ECS) is at maximum 0.6 °C and the best estimate of  is 0.268 K/(Wm-2 ) without any feedback mechanisms. The latest warming scenarios of Intergovernmental Panel on Climate Change (IPCC) for different CO2 concentrations until the year 2100 include the same feedbacks as the 2011 warming i.e. only water feedback. The ECS value of 3.0 °C would mean that other feedback mechanisms should be stronger than water feedback. So far there is no evidence about these mechanisms, even though 40 % of the change from 280 ppm to 560 ppm has already happened. The relative humidity trends since 1948 show descending development which gives no basis for using positive water feedback in any warming calculations. Cloudiness changes could explain the recent stagnation in global warming.