Even if the influence of the sun on climate change in recent decades has receded somewhat into the background, there are a number of researchers who are investigating the fluctuating effect of our central star on our Earth’s atmosphere, thus also on climate change – and who have produced surprising results in the process.
Henrik Svensmark, head of solar research at Denmark’s Technical University in Copenhagen, is one of them. And he ventures far ahead in the climate debate, the research with perhaps the greatest significance of our time. His research is contested, of course. Nevertheless, Svensmark and his critics agree that the topic “sun” deserves more attention in climate research. The participants are particularly interested in the complex interplay between our central star and ionizing emissaries from the depths of the galaxy – “cosmic radiation”.
Svensmark says: “The climate is influenced more by changes in cosmic radiation than by carbon dioxide”. CO2 has an effect, of course, “but it is far less than most current climate models assume, and also less than the influence of cosmic radiation”. In his opinion, a doubling of the greenhouse gas in the atmosphere would cause an increase in global temperature of at most one degree, and not two degrees, as is now generally accepted.
In other words, the “climate sensitivity” of carbon dioxide is only half as high as assumed. And as far as the changes in the natural CO2 balance of the earth’s atmosphere and those in temperature over millions of years are concerned, the greenhouse gas is rather “a slave to cosmic radiation and the global warming it causes, and not its ruler”. The amount of CO2 followed the warming by and large, not the other way around.
Last December, Svensmark again published a scientific study in the journal “Nature Communications” to support his thesis. The work is – at first – less about the sun itself than about how our climate and weather events are influenced by cosmic radiation, ionizing particles that permanently impinge on the Earth’s atmosphere. This is a particle stream that originates from exploding supernovae, that flows through the galaxy and finally, when it reaches the Earth’s atmosphere, exerts an influence on cloud formation, amplifying it.
The “missing link” or the gap in theory
This is where the sun comes into play: it modulates this particle flow decisively. That is why, says Svensmark, the sun is the main actor in the earth’s climate. Recently, together with his son and co-author Jacob, he explained the background and results of the new study in an interview with Benny Peiser.
The mechanism has been under discussion for many years. The influence of the sun on galactic radiation has long been undisputed. However, the extent to which their ionizing particles actually contribute to cloud formation has not been fully clarified. This has been the missing link, the gap in the cosmic ray-climate theory. With the contribution of the Danish researcher, which he wrote with Nir Shaviv of the Hebrew University of Jerusalem, among others, the scientists now claim to have identified that missing link. Not only theoretically, but also practically: through experiments in large chambers in which they were able to simulate the process of cloud formation in its first beginnings in large-scale experiments.
For the researchers involved, the chain is now closed: The particle flow hits the Earth’s atmosphere, ionizes microscopically small suspended particles, so-called “aerosols”, and causes them to expand, causing water vapour to condense on them and form clouds. And in the lower layers of the atmosphere, where they have a cooling effect on the earth’s temperature because they reflect the warming rays of the sun. Clouds in the upper layers, on the other hand, hold back the heat radiated onto the earth in the atmosphere, thus heating it rather than cooling it.
This process, which Svensmark and his colleagues are now claiming to have demonstrated, takes place with varying intensity, sometimes stronger, sometimes weaker – according to its reading depending on the moods of the sun: If the sun is very active, its magnetic field is particularly strong; it in turn emits ionising particles, the so-called solar wind, which however keeps off the other cosmic radiation, i.e. the cloud-promoting radiation, from the earth (the latter is also called “galactic cosmic radiation” for better differentiation from the “solar wind”).
This means that when the sun is active, less cooling clouds form and the earth heats up.
Sunspots as an early warning system
An active sun is accompanied by a higher number and a greater frequency of sunspots, which can sometimes even be observed with strong sunglasses, shortly before sunset, for example on the ocean horizon, when glare has diminished. Already at the turn of the 18th and 19th centuries, the German-British astronomer Wilhelm Herschel had registered a connection between sunspots and the climate and derived his “theory of the pork cycle” from this. However, the physical background remained hidden to him because the technical equipment of modern solar research was lacking. Perhaps the fat and lean years reported in the Bible are also due to the regular variations in solar activity.
Note: According to Svensmark’s research, the influence of the sun on the earth’s climate does not function through the variance of its warming rays, which indeed fluctuate extremely little – which is why many climate researchers deny their work all round, but possibly somewhat hastily. Svensmark says it is rather a subtle electrophysical effect. He assumes that the change in solar activity has a five to seven times stronger influence on climate fluctuations than the sun’s rays themselves.
A symptom that can be explained by this connection and in return confirms it stands out statistically: At a time when global warming has increased more than ever since measurements began, namely in the second half of the 20th century, the sun has been on average more active than at least in the last 8,000 years. This is generally accepted by the scientists of solar science. Nevertheless, it has so far played a subordinate role in leading climate research as an influencing factor for global warming. Also because this connection, starting with solar activity and cosmic radiation, the formation of clouds up to the global temperature could not be continuously detected. There was a gap in the detection chain between cosmic radiation and cloud formation.
Svensmark and his co-authors now assume to have closed exactly this “missing link”. It is, he says, a “breakthrough in understanding how cosmic radiation from supernovae affects cloud formation on Earth”, achieved through empirical experiments in its cloud chambers. That’s what the press release on the publication in “Nature Communication” says.
The study shows that “a change in the ionization of the atmosphere” does indeed influence the number of nuclei from which clouds are formed. The experiments in their chambers, in which they simulated the atmosphere and the play of ionizing radiation, would have resulted: According to the study, particles charged by cosmic radiation form clouds “several percent more frequently” than “neutral” particles. The tests had been repeated over 100 times to statistically clarify the signal.
The Cloud Explainers
Fluctuations in the solar wind cause the ion current to vary by about 20 percent. Svensmark and his colleagues now write that their experiments have resulted: This “twenty percent fluctuation in ion production can increase growth by one to four percent under pure conditions” (that is, the growth of the particles that form clouds). How strong this effect is in detail depends on regional differences and the corresponding cloud types.
The mechanism described fits another study by the Danish researchers who submitted it two years ago. They had found a correlation between sudden, strong weakening of the solar wind – so-called “Forbush decrease” – and changes in cloud cover. They now refer to this when they go further: It can be assumed that those fluctuations in particle growth of one to four percent could in turn “explain the changes in cloud cover of about two percent following Forbush decrease”. Two percent more or less cloud area does not sound significant at first. However, since the observation of global warming is about tenths of a percent of Celsius degrees, this natural effect could still play a role that should not be neglected.
For the authors, the physical experiments can be inferred congruently with the empiricism of climate events. According to Svensmark, this applies not only to the accelerated warming between 1970 and 1998, which was accompanied by record cycles of the sun, but also to the years 2006 to 2017, when extremely weak cycles were registered – parallel to a very high but hardly rising plateau of global temperatures. Such correlations could be traced many times over the last 10,000 years (not only the level of temperatures, but also the strength of cosmic radiation can be reconstructed over long periods of time).
The interplay is even clearer when looking at the last few million years, when temperatures rose or fell by 10 degrees more often, while our solar system during its march through the galaxy was exposed to a violent roller-coaster of regions with many or few exploding stars – and correspondingly fluctuating particle streams: “The mechanism could therefore provide a natural explanation,” the authors of the study write, “for the observed correlations between climate fluctuations and cosmic radiation, modulated by activities of either the sun or of supernovae in the vicinity of our solar system, observed over very long periods of time.“
Physical basis for historical observations
The researchers from Denmark and Israel are not the only ones who are investigating the relationship between cosmic radiation, the sun and the earth’s climate. The British particle physicist Jasper Kirkby documented very clear correlations ten years ago. Kirkby therefore also carries out physical experiments that are quite similar to the Danish experiments in order to find out the mechanism behind them. Together with the Frankfurt atmospheric scientist Joachim Curtius, he is conducting research at the European nuclear research centre CERN in Geneva, Switzerland, where he investigated the formation of clouds of aerosols and charged particles – also in a chamber, but also using computer models. And so wanted to derive the physical basis for historical observations.
Kirkby is head of the “Cloud” project (Cosmics Leaving Outdoor Droplets). Two years ago, CERN researchers published an interim result, but it was negative in this respect. In their experiments they could not (yet?) grasp the influence of ionizing radiation on the birth of cooling clouds. This is another reason why he is sceptical about the results of Svensmark’s study for the first time.
“Overall, the paper is interesting,” the CLOUD researcher attests to his Danish colleague, “the theoretical treatment in the paper is solid and the experiments seem to have been carried out properly.” But Kirkby distances himself from the importance of experiments with simulated cosmic radiation for the climate discourse: “In the main part, in the ‘discussion’, he is wrong, the assumptions are too optimistic about how relevant the effect is and how much it can be measured in its effects on the climate.”
He estimates the effects of additional ions, which in the case of stronger cosmic radiation accelerate the growth of aerosol particles and thus also the formation of clouds, “to a maximum of one percent”. In view of these fluctuations in cosmic radiation of only 20 percent, the effect moves at one or two tenths of a percentage point. “And this leads to an absolutely insignificant change in the droplets that are supposed to grow to the cloud.” Svensmark, on the other hand, says that his calculated effect of one to four percent is already calculated on the basis that the ion fluctuation is only 20 percent.
An interest in knowledge, two research locations, two different results. Although one thing is clear: the sun has a greater influence than some would like to believe in climate research. Svensmark believes he knows why the “cloud” experiments in Geneva did not have any significant effects on the assumed mechanism. He assumes that the Nuclei, which were examined in Geneva for their change by cosmic radiation, were “estimated to be too small by a factor of ten”. According to Svensmark, Kirkby also relied too much on numerical models in his study.
Here, however, Kirby criticises his Danish colleague: “Such experiments alone are not enough for the blanket statements from the paper, the effect must be presented in a global model, and if you use the results from Denmark for this, then I expect a negligible quantity will come out”. Svensmark also finds it a “good idea to study the effects on cloud formation further in a global model”, but he maintains that “our observations depict the entire relationship from cosmic radiation to aerosols and clouds”.
Researchers keep a low profile when it comes to the influence of the sun
“To have found the last piece of the puzzle in the interplay of sun, cosmic radiation, clouds and climate change, as the Danish researchers formulated it in their press release on the study, is indeed a high claim. This also raises doubts with another climate researcher, who himself is not one of the great Cassandra shouts when it comes to world climate. Even if he finds Svensmark’s approach important and negligently unnoticed so far.
The Hamburg climate expert Hans von Storch is known in the climate community above all for the fact that he considers climate research to be too strongly politicised. In his opinion, it is too one-sided on alarm, and economic interests have also played a role in the debate. Nevertheless, he also finds Svensmark’s press release “dubious” and considers the reliable result to be rather narrow and thus oversold. The paper was “subjected to a professional assessment,” says the professor at the Hamburg Institute of Meteorology. It seems to him that a subjunctive would have been more appropriate for the statements of the study here and there, even though he admits a rather limited expertise in cloud research.
And yet: Von Storch has no understanding for the fact that Svensmark’s contribution has so far been ignored in the climate debate. “Although it addresses a fundamentally controversial topic in the climate debate, namely the role of the changing effects of the sun, it has not been – or hardly – discussed in the public debate. He has not yet “heard anything about him” even in his scientific circles. He considers this “questionable”. On 10 June,“Welt am Sonntag” alone dealt with the topic in detail on a double page.
Von Storch’s adds to his lament about this reticence regarding Svensmark: In climate science, he says, the sun is something like a “hot potato”. His experience is that those who address the issue quickly burn their fingers among colleagues. Nobody wants to venture too far because too many people prefer to focus on carbon dioxide in order to advance the restructuring of the energy industry. Svensmark himself does not deny that CO2 is a greenhouse gas and that industrialisation contributes to global warming, but he believes that the sun is a stronger driver.
Nevertheless, those researchers who claim that all natural fluctuations – such as those of solar activity – can be neglected in their influence on climate change are leading the way, confirming Svensmark’s reservation: The two Max Planck Institutes working in the field – for solar system research in Göttingen and for meteorology in Hamburg – declined to comment on the paper in response to a request by “Welt am Sonntag”.
Svensmark critic Kirkby has no fundamental doubts about the significant influence of fluctuations in solar activity on climate change, at least over longer periods of time. Which is no surprise. In an article in the scientific journal “Surveys in Geophysics” 2008 (“Cosmic Rays and Climate”, with convincing graphics), he stated: With regards the Alps, as an example, the coinciding shifts in temperature and solar activity observed for at least 2,000 years would suggest the conclusion that these are “major” influencing factor on the climate. Kirkby describes it thus: The medieval warm period with “temperatures similar to today’s”, the Little Ice Age in the 17th century and its end, the somewhat weaker cooling at the beginning of the 19th century, the subsequent onset of global warming with a small bend towards the middle of the 20th century, the warming pause – all these curves all too clearly run along the rhythm of solar activity in Kirky’s diverse graphics.
Warmth? Cold? Rain? The answer is blowing in the solar wind
This was obviously not a regionally limited phenomenon, the connection is not only valid in the northern hemisphere, but could also be read from the development of the Andean glaciers, for example. The researcher from Geneva also collected extensive data for other parallels: in addition to temperatures, the rhythm of droughts and rainy years follows the rhythms of the sun. Warmth? Cold? Rain? Drought? Monsoon? The answer is blowing in the solar wind, one may read from Kirby’s historical studies, astonishingly clearly. Even if one takes into consideration that, in his opinion, the sun has lost the dominance in recent decades in climate developments to other factors – such as CO2, in palaeo-climate research, the influence of the sun is the decisive factor for Kirkby.
The cloud researcher says: “The correlations are far too numerous and too diverse to be dismissed them as coincidence.” He is particularly interested in the parallels that arise over periods of several hundred years. There, the fluctuations in solar activity are “the only possible factors that can be used as external factors for observed climate changes, perhaps combined with the regular internal oscillations in the atmosphere or the oceans”. It cannot be the warmth by the sun’s solar radiation itself, which has hardly changed during this period of time. But even if the effects are clear, the following doubt still applies to him: “We have not yet found the mechanism.”
What distinguishes Kirkby from Svensmark: The Danish scientist claims to have deciphered the secret behind this correlation, the physical mechanism, while the CERN researcher remains sceptical. Will he still continue to work in this field himself? After all, he himself has worked on it for decades. “Of course,” Kirkby answers, “it’s still an open question, of course I’m advancing this research.” And the new paper by his colleague Svensmark is also usable and worth reading. According to the current state of knowledge, there are only two conceivable ways in which sun and climate could be brought together: The ions from the cosmos and UV radiation, but this is absorbed in the stratosphere so that it has only a weak effect in the lower atmosphere.
Is too little account taken of the solar influence in the climate models? “It is quite simple,” Kirkby answers: “As long as a mechanism is not sufficiently depicted, the assumed effect – such as cosmic radiation – cannot be built into the models.” Is there a lack of money in solar research? “I don’t know how much is being put into this. Much funding, in any case, goes into the satellite-based exploration of the sun itself. Too little funding, however, is going into the relationship between the sun and the climate,” says Kirkby – and strives for reconciliation: “But I believe that the topic is being treated seriously in the climate debate.”
When it comes to the Roman climate optimum, the early medieval cold period, the high medieval warm period, the early modern “Little Ice Age” — everything seems to fit together with reconstructed solar activity, up to the warming during the middle of the 20th century, possibly with a delay of several years. But does this connection with our central star also apply to recent warming, from the 1980s onwards — and irrespective the fact that CO2, i.e. anthropogenic emissions, have long since interfered in developments as an “external factor”, however strong this may have been?
Is there a “hidden” warming?
Which could theoretically make a difference in this relationship between past and present: Industrialisation has, in popular terms, significantly polluted the air – a development that has been mitigated in developed countries thanks to growing environmental awareness, but which is all the more plaguing some emerging countries today. In the words of atmospheric researchers, this means that there are considerably more aerosols, suspended particles, especially sulfate particles, in the air. On the one hand, however, they reflect the solar radiation themselves, directly in other words, but they also transport the formation of clouds out of their tiny nuclei, thus having a double effect.
Has industrialisation thus intensified and accelerated the cloud formation process – compared to pre-industrial times, when the air was much cleaner and this process was thus much less? In other words, when a more effective environmental policy finally takes effect worldwide and today’s dirty, aerosol-rich air is purified, will global warming really accelerate? Are we therefore faced today with an additional, but hidden increase in temperature, which is only temporarily fogged by reflecting aerosols from industrial combustion plants and the cloud formation which it increases?
Climate research institutes and the Intergovernmental Panel on Climate Change (IPCC) have been holding this alarming view for some time. But the atmosphere and cloud researchers around Kirkby from Geneva have now been able to provide more clarity. In 2016 they published a study in the journal “Nature” that gave the all-clear regarding this “hidden warming”. “We were able to show that in a cleaner sky, the more natural particles emitted by trees become more effective.” Especially the secretions of pine trees, which were much more common at that time, played a role. Their natural particles, hydrocarbons, are all the more important for cloud formation, the less sulphates from the industrial chimneys darken the sky. According to studies in the Swiss mountains and in their cloud chamber at the CERN Research Institute, the cloud researchers have been able to empirically prove this. Therefore: “There will still be many clouds even when the sky is clean,” says Kirkby.
According to the CERN paper, climate models which assumed a “hidden” additional warming (i.e. blanketed by industrial air pollution) and which estimate probable global temperatures for the year 2100 from this assumption, have been about 50% off when assessing this effect. Says Kirkby: “It turned out that those climate models that predicted a very high temperature at the end of the 21st century are exactly those that assume a relatively cloudless pre-industrial world.” And that never existed.
Rather, the conditions of cloud formation before the Industrial Revolution were quite similar to those of today. This insight also led to a new view of the computer models, which should provide clues about global temperature in 80 years. They are neither particularly sharp in their statement nor can they be regarded as an expression of consensus in science.
The debate is far from over
The public climate debate today focuses almost exclusively on carbon dioxide and thus exclusively on human factors when it comes to the causes of climate change. At the same time, it is said that 97 percent of all experts in the climate research community are in agreement. However, what this agreement exactly is supposed to agree upon remains open as ever. Is it about rising temperatures? Perhaps this is still the closest agreement. Or is it about continuing warming in the future? That might make agreement harder. Above all, however, there is no agreement on the question of the actual extend of human influence. For many scientists, the relatively high temperature of the past three years, for example, is proof that the warming pause that began after the millennium is now over. Meanwhile, global temperature rose again, albeit rather slightly. Some don’t accept that the pause ever happened, but many do – and certainly not just the much-cited “climate sceptics”. Even the last report of the Intergovernmental Panel on Climate Change (IPCC) speaks of a “hiatus” in this context.
Others, on the other hand, see the real pause ahead of us. Among them are no other than James Hansen and Gavin Schmidt, the former and the present director of the Goddard Institute for Space Studies (GISS) of NASA. Both are otherwise rather well known for their warnings of a very big climate catastrophe. But recently, together with several other colleagues, they wrote a paper that warned that it was “plausible if not likely that climate change will give the impression of a hiatus over the next ten years”.
But why? Because of a combination of the solar cycle and a very strong El Nino 2016 – a regular anomaly in the Pacific, which was exceptionally strong and pushed global temperatures up sharply in 2015, 2016 and probably also 2017, but which have since settled back to the previously prevailing plateau. Schmidt and Hansen also say quite simply: “We must not underestimate the fluctuations of the sun in comparison to the imbalance in the energetic radiation balance”.
Time and again, today’s debate on climate change gives the impression that carbon dioxide is the sole cause of climate change and that expectations about its effects need to be constantly revised upwards. This certainly does not apply to Svensmark, Kirkby or others (such as Fritz Vahrenholt and Sebastian Lüning, authors of the book “The Neglected Sun” and publishers of the blog Die Kalte Sonne) who are researching the solar component of global warming. Neither of them questions the fact that CO2 is a greenhouse gas. In the last ten years, a whole series of studies have appeared which have assessed the “climate sensitivity” of CO2, i.e. its influence on temperature development, to be less than the Intergovernmental Panel on Climate Change (IPCC). It was almost overlooked that in its last report the IPCC itself has revised it downwards rather than increased its estimates.
The terms “climate deniers” and even “climate sceptics” are simply nonsense. This is especially true when it comes to researchers who only give different weight to the extent, causes or consequences of what is actually happening. It is no longer uncontroversial to ask how much global temperature will increase by the end of the century – and certainly not to ask what the human and natural contributions will. Those who ignore this and claim that the scientific debate is over are simply ignoring the dynamics of current research. After all, climate science remains exciting.
Original essay (in German) Die Sonnenallergie der Klimaforscher