On the Confusion of Planck Feedback Parameters

The Planck feedback parameter Λ₀ is the most fundamental quantity in the theory of global warming, because the surface temperature change ΔT_s,0 is calculated by—(radiative forcing due to CO₂ doubling)/Λ₀ in the absence of feedbacks other than that of surface temperature change. The following three groups of Planck feedback parameters are found in the literature depending on the choice of temperature T_s and the outgoing long wave radiation (OLR) at the top of atmosphere in equation of Λ₀ = −4OLR/T_s, which is derived from the Stefan-Boltzmann Law.

GROUP A: T_s = 288K and OLR = 231–243W/m² Λ₀ = −3.21 − −3.37(W/m²)/K

GROUP B: T_s = 255K and OLR = 242W/m², Λ₀ = −3.8(W/m²)/K

GROUP C: T_s = 288K and OLR = 492–514W/m² Λ₀ = −6.8 – −7.1(W/m²)/K

This study shows that Λ₀ of GROUP C is a theoretically relevant choice for T_s and OLR, rather than those of GROUP A and GROUP B, while the IPCC adopted Λ₀ of GROUP A. Although the surface temperature change Δ T_s is 3.0K with Λ₀ = −3.21(W/m²)/K for CO₂ doubling when lapse rate, water vapor, surface albedo and cloud feedbacks are included in the IPCC AR4, it is shown to be 0.5–0.75K with Λ₀ = −6.8(W/m²)/K in the present study.

Since the IPCC overestimates the threat of carbon dioxide by 4–6 times, the revaluation will be needed for the CO₂ reduction policies in terms of cost and potential hazards.