Francis Massen writes at his blog meteoLCD on The Kauppinen papers, summarizing and linking to studies by Dr Jyrki Kauppinen (Turku University in Finland) regarding the climate sensitivity problem. Excerpts in italics with my bolds

Dr. Jyrki Kauppinen (et al.) has published during the last decade several papers on the problem of finding the climate sensitivity (List with links at end). All these papers are, at least for big parts, heavy on mathematics, even if parts thereof are not too difficult to grasp. Let me try to summarize in layman’s words (if possible):

The authors remember that the IPCC models trying to deliver an estimate for ECS or TCR usually take the relative humidity of the atmosphere as constant, and practically restrict to allowing one major cause leading to a global temperature change: the change of the radiative forcing Q. Many factors can change Q, but overall the IPCC estimates the human caused emission of greenhouse gases and the land usage changes (like deforestation) are the principal causes of a changing Q. If the climate sensitivy is called R, the IPCC assumes that DT = R*DQ (here “D” is taken as the greek capital “delta”). This assumption leads to a positive water vapour feedback factor and so to the high values of R.

Kauppinen et al. disagree: They write that one has to include in the expression of DT the changes of the atmospheric water mass (which may show up in changes of the relative humidity and/or low cloud cover. Putting this into a equation leads to the conclusion that the water vapour feedback is negative and as a consequence that climate sensitivity is much lower.

Let us insist that the authors do not write that increasing CO2 concentrations do not have any influence on global temperature. They have, but it is many times smaller than the influence of the hydrological cycle.

Here what Kauppinen et al. find if they take real observational values (no fudge parameters!) and compare their calculated result to one of the offical global temperature series:

The visual correlation is quite good: the changes in low cloud cover explain almost completely the warming of the last 40 years!

In their 2017 paper, they conclude to a CO2 sensitivity of 0.24°C (about ten times lower than the IPCC consensus value). In the last 2019 paper they refine their estimate, find again R=0.24 and give the following figure:

Clearly the results are quite satisfactory, and show also clearly that their simple model can not render the spikes caused by volcanic or El Nino activity, as these natural disturbances are not included in their balance.

The authors conclude that the IPCC models can not give a “correct” value for the climate sensitivity, as they practically ignore (at least until AR5) the influence of low cloud cover. Their finding is politically explosive in the sense that there is no need for a precipitous decarbonization (even if on the longer run a reduction in carbon intensity in many activities might be recommendable.

Francis Massen opinion

As written in part 1, Kauppinen et al. are not the first to conclude to a much lower climate sensitivity as the IPCC and its derived policies do. Many papers, even if based on different assumptions and methods come to a similar conclusion i.e. the IPCC models give values that are (much) too high. Kaupinnen et al. also show that the hydrological cycle can not be ignored, and that the influence of low clouds cover (possibly modulated by solar activity) should not be ignored.

What makes their papers so interesting is that they rely only on practically 2 observational factors and are not forced to introduce various fudge parameters.

The whole problem is a complicated one, and rushing into ill-reflected and painful policies should be avoided before we have a much clearer picture.

Footnote: The four Kauppinen papers.

2011 : Major portions in climate change: physical approach. (International Review of Physics) link

2014: Influence of relative humidity and clouds on the global mean surface temperature (Energy & Environment). Link to abstract.   Link to jstor read-only version (download is paywalled).

2018: Major feedback factors and effects of the cloud cover and the relative humidity on the climate. Link.

2019: No experimental evidence for the significant anthropogenic climate change. Link.
The last two papers are on arXiv and are not peer reviewed, not an argument to refute them in my opinion.

Francis Massen (francis.massen@education.lu), a physicist by education, who manages and operates the meteo/climate station http://meteo.lcd.lu of the Lycée Classique de Diekirch in Luxembourg, Europe.

See Also my recent post More 2019 Evidence of Nature’s Sunscreen

Postscript:

Dr. Dai Davies summarized this perspective this way:

The most fundamental of the many fatal mathematical flaws in the IPCC related modelling of atmospheric energy dynamics is to start with the impact of CO2 and assume water vapour as a dependent ‘forcing’ .  This has the tail trying to wag the dog. The impact of CO2 should be treated as a perturbation of the water cycle. When this is done, its effect is negligible.

See Davies article synopsis at Earth Climate Layers