CO2 Sensitivity

CSS-3 This Climate Short Story is focussed on the theoretical CO2 Climate Sensitivity. The subject material is more technical than most of the previous discussions but is nevertheless a particularly important aspect of “Climate Change”. If you do not know CO2’s Climate Sensitivity, you don’t know what CO2’s contribution to global warming might be. And despite what the CAGW alarmist crowd tries to push, the CO2 Climate Sensitivity is not settled.

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The potential CO2 Climate Sensitivity range is quite remarkable, stretching from close to zero (based on the theory that the narrow CO2 energy Absorption Band is saturated at CO2 levels above roughly 350 ppm) to upwards of 4.5 °C (based on the IPCC’s assertion that the CO2 warming is reinforced with a positive water vapor feedback loop). The problem with the IPCC assertion is it lacks scientific credibility. There is no empirical proof that backs up their theory (a recurring problem with the IPCC and CAGW alarmists). Adding more water vapor to the atmosphere can lead to warming (after all water vapor is a much more important Green House Gas (GHG) than CO2). Unfortunately, for the CAGW alarmist crowd, water vapor tends to lead to more cloud cover and more precipitation (which both lead to cooling not warming). The IPCC’s 4.5 °C Climate Sensitivity is very misleading. Their CO2 Climate Sensitivity is around 1.2 °C (not much higher than the general consensus of roughly 1 °C). The 4.5 °C represents the high end of the IPCC’s water vapor “fudge factor”. And yes, until empirical data is available, it is a “fudge factor”.

A saturated CO2 Adsorption Band means the CAGW alarmist crowd is totally out to lunch. The University of Chicago’s MODTRAN model represents this concept quite well. The model’s output (energy radiating out to space) has been confirmed by satellite measurement. Adding CO2 above our current levels makes little difference to the energy levels being radiated out to space (i.e.: the absorption band is becoming saturated). The IPCC’s 1.2 °C estimate is plotted against both the 1.0 °C and MODTRAN CO2 climate sensitivity for comparison. Unfortunately, for the CAGW alarmist crowd, CO2’s climate sensitivity (based on human generated emissions) simply cannot generate catastrophic future temperature increases. The available empirical data limits the CO2 Climate Sensitivity to 1.35 C (but that assumes all the warming over the Modern Temperature Record (MTR, 1750 to the present) was CO2 based). Highly unlikely given that 80%+ of mankind’s CO2 emissions occurred post 1950 and roughly half of the warming occurred pre-1950.