Chapter 20 - Correcting Problems With the Conventional Basic Calculation of Climate Sensitivity

Abstract

The conventional basic climate model applies “basic physics” to climate, estimating sensitivity to CO2. However, it has two serious architectural errors. It only allows feedbacks in response to surface warming, so it omits the driver-specific feedbacks. It treats extra-absorbed sunlight, which heats the surface and increases outgoing long-wave radiation (OLR), the same as extra CO2, which reduces OLR from carbon dioxide in the upper atmosphere but does not increase the total OLR. The rerouting feedback is proposed. An increasing CO2 concentration warms the upper troposphere, heating the water vapor emissions layer and some cloud tops, which emit more OLR and descend to lower and warmer altitudes. This feedback resolves the nonobservation of the “hotspot.” An alternative model is developed, whose architecture fixes the errors. By summing the (surface) warmings due to climate drivers, rather than their forcings, it allows driver-specific forcings and allows a separate CO2 response (the conventional model applies the same response, the solar response, to all forcings). It also applies a radiation balance, estimating OLR from properties of the emission layers. Fitting the climate data to the alternative model, we find that the equilibrium climate sensitivity is most likely less than 0.5°C, increasing CO2 most likely caused less than 20% of the global warming from the 1970s, and the CO2 response is less than one-third as strong as the solar response. The conventional model overestimates the potency of CO2 because it applies the strong solar response instead of the weak CO2 response to the CO2 forcing.