Press Release 8 Jan 2026

The water feedback does not follow the theory of the IPCC science

Positive water feedback has been a cornerstone in any Global Climate Model (GCM). In the AR5, the IPCC writes that “water vapour is a strong and fast feedback that amplifies any initial forcing by a typical factor between two and three.” The latest research study of Dr. Antero Ollila shows that, according to the empirical observations, the maximum warming feedback amplifies the original radiative forcing by a factor of 1.14 (14 %). In the AR6, the Climate Sensitivity Parameter (CSP or λ) is 0.47 K/(Wm-2), which means water feedback amplification by a factor of 1.8 (80%) since the CSP is 0.265 K/(Wm-2) without water feedback.

Dr. Ollila has calculated the first time the radiative forcing (RF) equation for different water vapour concentrations in the same way as for other greenhouse gases by applying the spectral analysis method. Ollila says that “this is a kind of 'silver bullet' solution, since in this way, the question of the magnitude of water vapour feedback can be solved simply by calculating the RF values of water vapour using the observed global humidity observations.”

A greatly oversized water vapour feedback can be found in the AR6 warming calculations, in which the observed and the GCM-calculated temperature increase from 1750 to 2019 is practically the same, 1.27ºC - 1.29ºC. A closer analysis reveals that the RF value of cloud-aerosol-radiation has decreased by -0.12 Wm-2 from 2011 to 2019, but during the same period, the absorbed solar radiation (ASR) due to decreased cloudiness has increased 1.29 Wm-2, which obviously has not been included in this RF driver. The reason may be that, according to the IPCC science, the warming impact of this ASR increase is 0.6 ºC, which would make the GCM-calculated temperature increase to be about 1.9 ºC – 2.0 ºC. This an evidence that the water vapour feedback applied according to the IPCC science gives far too high GCM-calculated temperatures.

Source: Antero Ollila, Adj. Prof. Aalto University (Emer.), aveollila@yahoo.com, Phone +358 44 2437365
More information: https://www.climatexam.com/single-post/water-feedback-does-not-follow-the-theory-of-the-ipcc-science

The water vapour feedback theory of the IPCC would mean that the temperature impacts of water vapour should be about the same as the absorbed solar radiation warming impacts, but they are only about 14 % of the total temperature change.

The fitted curves (dotted lines) of water vapour RF dependency on the humidity concentration.

There is no water vapour feedback in the Ollila-2 model simulations, but only the warming impacts of greenhouse gases and absorbed solar radiation. In the IPCC model simulations, water vapour feedback has been applied according to the climate sensitivity parameter of 0.47 K/(Wm-2) in the AR6.