Something unusual and encouraging has happened in Danish climate journalism. Berlingske, one of Denmark’s leading national daily newspapers, has published an excellent and genuinely inquisitive article about the dismissal of physicist Henrik Svensmark from the Technical University of Denmark (DTU), where he has been working since the late nineties. The headline leaves no room for doubt: “Controversial Danish climate and space researcher has received the pink slip from DTU: It is ‘a death blow’ to my research”.

Here is how the article starts:

He is one of Denmark’s most internationally recognized researchers – and at the same time one of the most controversial. But now space and climate researcher Henrik Svensmark has, in his own words, been “good old-fashioned fired” by his employer, the Technical University of Denmark (DTU) in Lyngby. He does not rule out that “political considerations” – as he puts it – were involved in the years-long process that led to his final dismissal. At the same time, Henrik Svensmark does not hesitate to call it “a death blow” to a branch of research that he has largely developed single-handedly and that climate researchers around the world, including the UN’s climate panel (IPCC), have had to relate to – often reluctantly. This is mainly because Svensmark’s research points to what he sees as an overlooked natural factor behind a large part of the climate changes Earth has undergone. He finally does not rule out that the dismissal may be linked to the fact that he is perceived as a controversial researcher in wide circles: “There is nothing controversial about the research itself. But it is true that many perceive my research as controversial, even though it shouldn’t be.” DTU has no comments on the actual dismissal of Svensmark and refers to it as a personnel matter. However, the director of DTU Space, Henning Skriver, confirms that Svensmark’s overarching research area, atmospheric physics, will now “be significantly down-prioritized.”

Science journalist Lars Henrik Aagaard deserves credit for the whole article. Rather than dismissing Svensmark as merely ‘controversial’, he asks the essential question: is DTU retiring an ageing employee, or is it terminating an internationally recognized but scientifically inconvenient research program?

The facts reported by Berlingske are troubling.

Svensmark, aged 68, and well known for his work on cosmic rays and clouds, was still actively working and preparing a new experiment. Only a few months earlier, he says, his superiors had told him that his research was important and that they wanted him to continue.

According to Svensmark, he had also been selected for a professorship in 2016 following positive international evaluations. A new rector however, blocked his expected promotion to full professor, downgrading him to Senior Researcher (and lowering his salary). That move made it harder for him to secure regular research funding in Denmark.

In 2021, DTU again attempted to dismiss him, but he continued, partly, he says, because of protests from scientists connected with MIT and Princeton (Lindzen and Happer).

Berlingske presented this history to DTU. The university declined to address it. DTU Space director Henning Skriver merely stated that atmospheric physics was being “significantly downgraded” as part of a strategic prioritization.

That is not an explanation. It is management fog.

A public university may change its priorities. But it should explain the scientific reasoning. Why was Svensmark encouraged to continue only months before his dismissal? What happened to the positive international evaluation? Why was the professorship removed? Why is an active experiment being stopped?

The details of an individual employment case may be confidential. The scientific grounds for closing a research program shouldn’t. A hypothesis cannot be dismissed administratively

Solar activity

Svensmark’s research concerns the influence of solar activity and cosmic radiation on aerosol formation, clouds and therefore the climate.

The proposed mechanism is straightforward in principle. Solar activity affects the amount of cosmic radiation reaching Earth. Cosmic radiation ionizes the atmosphere. Ionization may influence the formation and growth of aerosol particles, some of which become cloud condensation nuclei. Clouds, in turn, strongly affect Earth’s radiation balance.

Parts of this chain have been demonstrated experimentally. The unresolved question is how large the resulting climate effect is under real atmospheric conditions and over different timescales.

Svensmark does not claim that carbon dioxide has no effect. He told Berlingske:

“I am not saying that humans are not part of it.”

His point is that natural variability, cloud processes and solar influence remain insufficiently quantified. He describes the dismissal as “a death blow” to the research program he has spent much of his career developing.

Not a marginal researcher

Svensmark cannot reasonably be dismissed as an unsuccessful or marginal scientist. Google Scholar records more than 7,000 citations to his work and an h-index of 30. Compared with the broader DTU research community, this places him approximately among the upper fifth of researchers and probably higher when measured by total citations. That is a considerable scientific impact for a relatively small and highly contested research field, far removed from the large collaborative networks that generate many citations almost automatically.

The predictable but weakest contribution in the article comes from Jens Hesselbjerg Christensen, professor at the Niels Bohr Institute and a prominent figure in the IPCC community.

Hesselbjerg accepts that cosmic radiation may play a role in cloud formation and long-term climate history. He then claims that much of Svensmark’s research appears to have been designed to confirm his hypothesis and that, whenever it was not confirmed, “an arm or a leg” was simply added.

That is an extraordinary accusation and an intellectually shabby one.

Hesselbjerg identifies no paper, no experiment, no faulty measurement, no improper method and no failed prediction. He merely insinuates that Svensmark has constructed his research to reach a predetermined conclusion. If Hesselbjerg believes that, he should name the experiments and explain precisely what was wrong with them. Otherwise, he should withdraw the allegation.

Developing a hypothesis as new evidence appears is not scientific misconduct. It is science. Aerosol formation involves nucleation, particle survival, growth, atmospheric chemistry and eventual cloud formation. Discovering additional mechanisms is not “adding an arm or a leg”. It is the whole purpose of experimental research.

Hesselbjerg’s performance illustrates a wider problem. Researchers close to the institutional consensus can invoke authority while providing remarkably little argument. A dissenting researcher is expected to prove every link in a complex physical chain before his work is even considered legitimate.

That is not a scientific level playing field.

The research should continue

The immediate objective should not merely be to embarrass DTU. It should be to ensure that Svensmark’s research survives. The most important next step is to develop a climate model that explicitly includes the proposed chain connecting solar activity, cosmic radiation, atmospheric ionization, aerosol growth and clouds, alongside greenhouse-gas forcing and the other established climate mechanisms.

Such a model would make it possible to test a question of enormous scientific and political importance: How much of the observed temperature development is caused by human influence, and how much is caused by natural variation?

That question is far from purely academic. Climate policy depends critically on the answer. If natural influences are larger than assumed, the expected effect of reducing carbon emissions is smaller. If they are negligible, the current attribution of climate change to CO2 becomes stronger. Either result would be valuable.

As explained by Henrik Svensmark: “The next decisive step is to build a climate model in which the influence of solar activity, cosmic radiation, aerosol growth and clouds is represented together with greenhouse gases. That would allow us to test how much of modern climate change is human-caused and how much is natural. This can be done within a few years and with a research budget that is modest compared with the political and economic importance of the question.”

The task is therefore concrete: we need to find a new institutional home for Svensmark, preserve the equipment and scientific expertise, assemble an international research team and raise the necessary funding.

Berlingske has performed a valuable public service by bringing this case into the open. DTU has responded with evasion. Jens Hesselbjerg Christensen has responded with an undocumented attack on a colleague’s scientific integrity.

Neither response is acceptable.

Science advances through experiments, observations and testable models, not through administrative priorities, institutional conformity or casual insinuations.

Henrik Svensmark’s research must not end with a DTU management decision. It must now be given the resources to face the only judgement that matters: the judgement of observations.