By Ad Huijser (corresponding address ah@on.nl)
Summary: By applying a simple feedback model for the response of the atmosphere to GHG-forcing at TOA, the GCM’s CMIP3/5 derived climate feedback values are being discussed in view of a.o. the CERES satellite data about trends in globally averaged surface temperatures and diminishing cloud-cover. It is shown that the trends in cloudiness during the period 1980-2020 are inconsistent with a CO2-only scenario, unless accepting extremely high ECS values of around 8K/2xCO2. Taking those trends in cloudiness as extra, independent forcing, results in a value of the climate sensitivity for the change in cloud cover of about 0.09 K/%cc. With that value inserted in the feedback model, it is shown that the often debated “sum of feedbacks” that significantly amplify the effect of increasing CO2 levels are reduced to almost zero, yielding an ECS of only 1.1 K/2xCO2 instead of the high values as promoted by the IPCC in their climate projections based upon this AGW-hypothesis.