Substack, Anastassia Makarieva: On the scientific essense of Dr. James Hansen’s recent appeal

Dr. James Hansen, one of the voices informing the society about global warming problems, in a recent public appeal co-authored by Dr. Pushker Karecha made the following strong statements (my emphasis):

Criticisms of the Acceleration paper in the media [a recent paper by Hansen et al. — AM] did not address the physics in our three assessments of climate sensitivity. Instead, criticisms were largely ad hoc opinions, even ad hominem attacks. How can science reporting have descended to this level? Climate science is now so complex, with many sub-disciplines, that the media must rely on opinions of climate experts. Although there are thousands of capable scientists in these disciplines, the media have come to depend on a handful of scientists, a clique of climate scientists who are willing, or even eager, to be the voice of the climate science community. But are they representative of the total community, of capable scientists who focus on climate science?
We have lamented[9] the absence of scientists with the breadth of understanding of say Jule Charney or Francis Bretherton,[10] or our beloved, sometimes crotchety, former colleague, Wally Broecker. However, the truth is that there are many scientists out there with a depth of understanding at least as great as the clique of scientists that the media rely on. Given the success of this clique in painting us as outliers, we are dependent on the larger community being willing to help educate the media about the current climate situation.

I will not use the word ‘clique’ below, as it appears to me that it has a negative connotation. I will replace it with the more neutral ‘core’ — ‘the core climate scientists’. Not being a native speaker, I did not consult ChatGPT on whether this phrase is good English, so if it does sound a little awkward please accept it as a human touch.

Many of the readers of this blog are, like myself, concerned about the fact that the biosphere is largely neglected in the on-going climate discussions. These readers may wonder why Dr. Hansen, who follows the same CO₂-focused narrative as the core climate scientists, has been, in his own words, painted by them as an outlier.

This is because Dr. Hansen states that the climate sensitivity to increasing CO₂ is higher than IPCC’s, while the core climate scientists have been rigorously advocating against climate models with a higher than IPCC’s sensitivity, and not without a reason. Here I will share my perspective on this controversy and how it may relate to the recognition (or continued neglect) of a major role of the biosphere in the on-going climate destabilization.

Mistreatment of Hot Models?

Everybody interested in climate problems should know that climate models differ greatly in their projections of how much the planet could warm if the atmospheric concentration of CO₂ doubled.

The above graph (Fig. S7 from Zelinka et al. 2020) shows how different global climate models developed in different research centers around the world project planetary warming corresponding to doubled CO₂ (ECS stands for Equilibrium Climate Sensitivity). Different colors represent relative contributions from different processes. Blue colors stand for the radiative forcing contribution from increased concentrations of greenhouse gases (CO₂ and water vapor). Red colors are the albedo changes. Green colors are changes in the lapse rate and relative humidity. Yellowish colors represent cloud impacts. TR and EX mean tropics and extratropics. Models in the first five-six top rows were termed ‘hot models’, as they project much more warming than the others.

For example, model INM-CM4-8, the last row in CMIP6, predicts the lowest temperature increase from CO₂ doubling, around 2 K. This is, by the way, the model developed in Moscow University in Russia. This model has a tiny, and negative, cloud feedback. This means that as the planet warms, clouds in this model change in such a manner as to offset (a miniscule part of) the warming. INM-CM4-8 also has a very small contribution from changes in albedo.

Conversely, model CanESM5, the first row in CMIP6, coming from Canada, projects a nearly 6 K warming for CO₂ doubling, with a large part of this response due to the destabilizing cloud feedback. Such strong feedbacks were missing in the previous generation of climate models (cf. model CanESM2 in CMIP5). The appearance of this strong cloud feedback in some of the CMIP6 models resulted from intense work by researchers striving to represent cloud response to temperature changes as robustly as possible, also using the new data unavailable for the models of the previous generation.

Having described clouds to the best of their capacity, and having changed the models’ codes accordingly, the researchers ran simulations with increased CO₂ and found that their models now predict much more warming than before.

After many discussions not all of which can be traced in the literature, the core climate scientists came to the conclusion that such models can’t be true. Accordingly, in the IPCC report their contribution to the climate projections was downplayed.

Dr. Sabine Hossenfelder even made an angry video about this suspicious procedure of a posteriori excluding the most alarming results that did not conform to expectations. More recently though, she softened her emotional stance and suggested that the climate scientists could have thrown away the hot models just because they were all humans and wanted “to get rid of bad news as much as everyone else.”…

…Community outlook

Dr. Hansen appeals to the broader community who should have an understanding “at least as deep” as the core climate scientists. It remains unclear, however, how those additional scientists with an equally deep understanding of climate problems are going to argue with other deeply understanding scientists. Maybe they will support the core climate scientists and not necessarily Dr. Hansen. We should see.

My respectful questions to Dr. Hansen would be: would you be willing to contribute to opening the climate discussion wider than just including your own team’s interpretation of what’s happening? Is this discussion going to be open only for people “with a deeper understanding” of all climate issues, whoever defines that deep understanding? Or is it possible that some critical pieces of evidence can be brought in by people who may not be equally informed in all areas of climate science?

Currently if a person does not know something in the quite complex physics of the greenhouse effect, such a person stands a non-zero chance of being ridiculed and excluded from climate discussions. But if a person is ignorant about the processes in the biosphere, it is just fine, such a person faces no constraints in submitting authoritative opinions about our planetary perspectives. And we are all ignorant about these processes — as Bar-On et al. 2025 have just shown, after decades’ of research, we don’t even know where the carbon goes.

With regard to the biosphere, one’s experience of natural ecosystems sets a certain standard of what complexity is. It might be easier to brush off the biosphere trusting a model that says that the biosphere does not matter for a modeller who has never experienced the complexity of a natural forest. Depauperacy of nature experiences can be subtly influencing thinking patterns. In this situation opening the dialogue more widely to include and tolerate all people with a good will to improve the situation could be a good strategy. Probably Dr. Hansen, having experienced how unproductive excluding other opinions’ as outliers could be, could be in a unique position to facilitate such a more inclusive discussion, for the sake of preserving the biosphere.