HomeNatureClimate marked by the Sun

Climate marked by the Sun

dr Tomasz Mrozek
an astronomer working at the Astronomical Institute of the University of Wrocław
and the Sun Physics Department of the Space Research Centre of the Polish Academy of Sciences, about the relationship between the Sun and the climate.

Tematem przewodnim trzeciego wydania magazynu ClimateNow! jest Słońce i jego wpływ na zmiany klimatu. Czy faktycznie zachodzą one z powodu zmian na Słońcu? A może jednak w wyniku działalności człowieka? O związek między Słońcem, a klimatem zapytaliśmy dr Tomasza Mrozka, astronoma pracującego w Instytucie Astronomicznym Uniwersytetu Wrocławskiego i w Zakładzie Fizyki Słońca Centrum Badań Kosmicznych Polskiej Akademii Nauk.

What is the Sun and how does it affect the climate on Earth?

– The Sun is a star. That’s in the first place. As much as 75% of the mass of the Sun is hydrogen and the rest is mostly helium. Elements such as oxygen, carbon, iron or neon constitute a total of about 1.7% mass of the Sun. The Sun is a relatively small star. Some of its features result from this fact. The sun is the so-called dwarf, which due to its low mass has very specific ways of transporting energy from within. By transforming hydrogen into helium, the Sun generates enormous energy that must be transported to the surface so that the star will not fall apart. In this process, every second, the sun produces about 1026 joules of energy, which is comparable to the energy of a power plant with a capacity exceeding 1026 watts. To put it more vividly – let’s imagine that energy from just one second would last for a few million years of functioning of the Earth’s energy systems. That’s really a lot.

Mówiąc bardziej obrazowo – wyobraźmy sobie, że energia z tylko jednej sekundy starczyłaby na parę dobrych milionów lat funkcjonowania ziemskich systemów energetycznych. To rzeczywiście bardzo dużo. 

In the process of transporting energy from the nucleus, energy is first carried by radiation, then by convection. The boundary region between the radiative and convective layers (tachocline) is simultaneously the area in which the Sun stops rotating like a solid body and begins to behave more like a normal fluid. The sun, for the most part, consists of charged gas particles that, moving in the tachocline and convective zone, naturally generate and strengthen the magnetic field. This makes the Sun a magnetically active star. Very strong energy is accumulated in the solar magnetic field. When twisted, high-energy magnetic structures that naturally tend to a state of lower energy float to the surface, the configuration of the fields and their merging change. The phenomenon of merging and fast change of field configuration is called reconnection. Reconnection is the cause of coronal mass ejections in the Sun, solar flares and magnetic storms caused by them. It also causes impulsive heating of the corona. During transition, the energy of magnetic fields is released. It is then transferred to heating gases in the solar atmosphere and accelerating the particles to higher energy. The process takes place within minutes, and energy of 1025-1026 joules, and even more, is released. Solar flares are characterized by temperatures exceeding 20 million degrees. It is a very sudden phenomenon that happens in a large area, because the biggest flares can occur in areas of tens of thousands of kilometres.

Another process is the so-called coronal mass ejection (CME). This may be associated with flares and sometimes occurs spontaneously, but it is also a phenomenon that is associated with the reconnection of magnetic fields. CMEs are energetically comparable to solar flares, while their range and scale of impact on the Solar System is completely different. They move in interplanetary space. Coming away from the Sun, they reach very high velocities – often exceeding 2,000 kilometres per second. This causes them to reach Earth as well. Coronal mass ejection is one of the elements, possibly even the key one, which disrupts the immediate cosmic environment of the Earth and Earth’s magnetosphere. There are different kinds of related threats, such as communication disruptions, destruction of energy networks, as well as auroras. From the climate point of view, CME is a less significant phenomenon, because it is short-lived – lasting several, sometimes several dozen hours.


The sun is extremely active. This activity has, at least indirectly, an impact on the climate. Is this impact weakening or growing?

– The magnetic field and the associated number of active phenomena, such as flares, coronal mass ejections and a few others, are phenomena connected with the solar magnetic activity. The level of activity is in turn associated with the so-called sunspots, i.e. darker areas observed on the surface of the Sun, whose characteristic features are temperature lower than the ambient temperature and an intense magnetic field. A lot of spots on the surface of the Sun means a lot of magnetic fields, a lot of active phenomena, so high activity of the Sun. Of course, this activity is not the same. Sunspot activity cycles are about every eleven years, with some variation in length. In short, every 11 years there are times when there are very few or no spots on the surface of the Sun. There is always a time between two minima when there are a lot of spots. The point of highest sunspot activity during a cycle is known as solar maximum. Individual maxima are different. Sometimes there are more spots compared to individual maxima, sometimes fewer. This may result from the overlapping of several cycles of activity of different lengths. In the mid-20th century, in the 1950s, 1960s and 1970s, the solar maxima were very strong. And at the same time the last one was very weak. The sun was active and generated strong phenomena but compared to the previous several cycles of activity, it was clearly weaker. On the other hand, the last and penultimate minima, i.e. the current and preceding one, were interesting phenomena. It was the lowest minimum in about 100 years, the Sun as calm as observed today, and also 10-11 years ago, was at the beginning of the 20th century.

Ciekawym zjawiskiem było z kolei ostatnie i przedostatnie minimum, czyli obecne i to poprzedzające je. To było najmniejsze minimum od około 100 lat, Słońce tak spokojne jak to obserwowane obecnie, a także 10-11 temu, było na początku XX wieku. 

What are the effects?

– We do not quite know the consequences, although we try to understand them. We know that cyclicalities can overlap from time to time and that the magnetic activity of the Sun stops for many years. We observed such a period at least once, not so much as weakening, but the practical extinction of the Sun’s activity. In the second half of the 17th century, there were very few spots, and records from this period mention single spots. Definitely, the reason was not weak observational instruments, because telescopic observations were already being carried out at that time. Galileo himself and a whole range of contemporary scientists conducted observations of the Sun and spots were already observed. Fortunately, there are so many observations that thanks to them it was possible to reconstruct the course of activity cycles, including those from the beginning of the 17th century, while the second half of the 17th century was very inactive. At the same time, historical reports show very severe winters in the northern hemisphere. Is this a coincidence or a connection between the Sun and the Earth?

W tym samym czasie w relacjach historycznych pojawiają się informacje o bardzo ostrych zimach na półkuli północnej. Czy to zbieg okoliczności, czy jednak sprzężenie między Słońcem, a Ziemią?

The working hypothesis is that this relationship between the Sun and Earth exists. The premise is what was observed in the second half of the 17th century, i.e. the relationship between low solar activity and severe winters. There are also a lot of historical accounts that could confirm this. Beginning with paintings on which a market on the frozen Thames was presented, which is unimaginable today, through accounts of the frozen Baltic. Of course, we must interpret it correctly. The Baltic Sea did not freeze as a whole, the bays froze, and in fact it enabled regular connections with Sweden along routes along which taverns and horse exchange points were erected, including in the Gulf of Finland.

Bałtyk cały nie zamarzał, zamarzały zatoki i faktycznie umożliwiało to regularne połączenia ze Szwecją traktami, przy których stawały karczmy i punkty wymiany koni m.in. w obszarze Zatoki Fińskiej.

The Polish hymn mentions this fact: “Like Czarniecki to Poznań returned across the sea” (text according to Wybicki’s original manuscript – editor’s note) or in the modern version: “Like Czarniecki to Poznań (…) We shall return across the sea”. In fact, Czarniecki and his army crossed the frozen Als Strait (Alssund). These are obviously historical threads. They suggest, however, that such a relationship could exist, but it is difficult to determine to what extent. Especially given the fact that the observations relate to short periods of time.

Is there any other way to determine the level of solar activity?

Yes, the method is to measure radioactive isotopes, carbon (14C) and beryllium (10Be). Isotope abundance clearly correlates with solar activity. This paves the way to quantitative measurements and reaches back in time further than the last 400 years. Thanks to this, solar variability can be reproduced for a thousand, 10 thousand years. In the period climatologists call the Medieval Climate Optimum (the period between the 9th and 12th-13th centuries AD), when (local) temperatures were slightly higher, grapevines were cultivated in Poland, and Viking settlements were located in Greenland. It is difficult to say whether it was a green island, although the conditions allowed people to settle on it. The analysis of geological records resulting from measurements of radioactive isotopes indicates that solar activity was then increased.

So is this direct evidence that the relationship between the Sun and the Earth’s climate exists?

Undoubtedly, the Sun provides energy.

Można powiedzieć że całkowicie zależymy od „humorów” Słońca, z punktu widzenia całkowitej energii którą dostarcza, tego co produkuje we wnętrzu, a następnie wypromieniowuje. Poziom wypromieniowanej energii jest bardzo stabilny, on się troszeczkę zmienia wraz z cyklem aktywności słonecznej, ale ta zmiana jest na poziomie ułamków promila.

We can say that we completely depend on the „moods” of the Sun, from the point of view of the total energy it provides, what it produces inside, and then radiates. The level of radiated energy is very stable, it changes a little with the solar activity cycle, but this change is at the level of fractions of a per mile. This is not much and from the climate point of view, it has long been decided that fluctuations in the supply of radiant energy are too small to have significant effects on Earth. Magnetic activity is a set of solar factors and impacts on Earth completely different from the radiation flux that reaches the Earth.

If the changes in the amount of radiation reaching the Earth are so small, why do we see correlations between periods when it was cooler and periods of lower solar activity and vice versa?

Here the direction of research is completely different, we are not dealing with solar radiation, but with magnetic fields and active phenomena that are visible or observed in the stellar corona. From the point of view of people on Earth, we know that we live in a centre that we call the heliosphere. A very thin layer, something that is a natural extension of the stellar corona and the outer layer of the Sun’s atmosphere, a natural extension into the interplanetary space. The heliosphere is shaped by the solar wind, which is a stream of charged particles, emitted by the sun in all directions.

Heliosferę kształtuje wiatr słoneczny, będący strumieniem naładowanych cząstek, emitowanych przez Słońce we wszystkich kierunkach.

Can the heliosphere and its changes affect what is happening on Earth?

Research from the turn of the century – the end of the 1990s and the beginning of the 2000s, show that correlations were visible. During periods of low magnetic activity of the Sun, we observe periods of greater cloudiness with low clouds. Cosmic and galactic radiation reaching from different places in the galaxy, i.e. particles like protons, high energy radiation quanta, or atomic nuclei (e.g. of iron), falling into the atmosphere, have a high speed and by hitting everything they encounter on their way, they transmit some energy. This is the basis of the process that causes the appearance of air showers in the Earth’s atmosphere. Such an air shower is a structure with a width of several dozen kilometres, extending for several hundred meters, or even several kilometres at the surface of the Earth (structures generated by a single particle). Scientists were interested in whether such air showers, in some layers of the atmosphere, when the conditions are favourable, can foster the condensation of water vapour. The main figure of this research is Henrik Svensmark, a scientist of the Danish Space Research Institute. He caused an uproar by suggesting that high-energy cosmic rays could lead to more clouds forming and cooling the climate, and vice versa. That the varying strength of the solar wind – a stream of charged particles released from the sun – can lead to changes in the cosmic ray flux. This did not match previous climate balances. Everyone, however, failed to see that Svensmark does not want to prove that people have no influence on the Earth’s climate. Svensmark has found a factor that is able to keep it under control to some extent. This is not an explanation. Simply the correlation between cosmic rays and cloud cover, and hence, naturally, the researcher’s question about the source of the phenomenon.


These are very interesting correlations.

Yes, indeed. What is particularly interesting is the theory of the Russian physicist Alexander Guriewicz from the early 1990s, who suggested that lightning was caused by cosmic rays. However, the potential difference between the cloud and the Earth is too small to explain such a large number of observed lightning strikes. Nevertheless, there are discoveries that confirm that a large part of lightning could be explained by the incoming particles of cosmic rays. In periods when there is less cosmic radiation near the Earth’s surface, there are also on average fewer lightning strikes in places where they are usually numerous. There are premises that show the relationship between what is happening on Earth, even close to the surface, and the amount of cosmic radiation reaching its surface. The number of cosmic rays reaching the Earth is closely related to the level of solar activity. During periods of high activity, when the Sun releases a lot of mass ejections into the interplanetary space, they fill the entire heliosphere. Coronal mass ejection is a tangle of magnetic fields and particles. The heliosphere is filled both with a disturbed magnetic field and particles, and this causes the Solar System to be better shielded from cosmic rays from outside. They find it harder to penetrate the inner areas of the Solar System, into the regions where the Earth orbits around the Sun. When the Sun is less active, there are fewer phenomena, especially coronal mass ejections. We know that there is a relationship between the state of the heliosphere and the amount of cosmic radiation, and at the same time we see that at the Earth’s surface this radiation – if it reaches here – can have measurable effects. Therefore, we expect them, and observe the modulation of these effects with the activity of the Sun.

Kiedy Słońce jest mniej aktywne, zjawisk jest mniej, szczególnie koronalnych wyrzutów masy. Wiemy, że jest związek miedzy stanem heliosfery, a ilością promieniowania kosmicznego, a jednocześnie widzimy że przy powierzchni Ziemi to promieniowanie – jeśli tu dociera, to może wywoływać mierzalne efekty. W związku z tym oczekujemy ich, i obserwujemy modulację tych efektów z aktywnością Słońca.

The scale is something completely different. Currently, we are not able to state it clearly, although in the IPCC (Intergovernmental Panel on Climate Change) report there is a resounding reflection that the border has been crossed and the effects of modulation of the Earth’s climate by the Sun are masked by human activity. If I were to answer the question of whether the Sun affects the Earth’s climate, then I can state that it does and sign with both hands under this statement. However, the ratio between this influence and human activity is a completely different issue.

The Parker Solar Probe was sent to the Sun to determine why the outer corona is much hotter than its surface, and how it relates to the magnetic field. The mission of the solar probe is considered one of the most important in human history. What will we learn from the test results?

The Parker Solar Probe is a probe whose mission is primarily to investigate what is happening in the solar wind, both during periods of low and high solar activity. From the perspective of time in which this probe has worked (we currently have the fourth approximation to the Sun), for now we are learning what is happening within a single cycle of activity. We are now at a minimum, so in fact the Parker probe is investigating what solar wind looks like near the Sun during the minimum period. It turns out that the wind is much more unpredictable than it seemed before, that there are small structures that at the distance of one astronomical unit (as we are from the Sun) are blurred and therefore have not been observed before. The Parker Solar Probe is the first probe to come so close to the Sun. Now it is near the perihelion, at a distance of less than 20 million kilometres, ultimately in 2024 it will approach the photosphere – its conventional outer shell – at a distance of 6 million kilometres. The Parker Solar Probe reveals small structures in the wind, very small changes in terms of size scale, magnetic field returns; it can be seen that this area is much more unpredictable and turbulent than it was previously thought. If the probe lasts a few years, long enough to describe what the variability of these areas looks like during the activity cycle, then it can be said that the probe will begin to discover the secrets of many years of solar activity.

Jeśli sonda przeżyje kilka lat, na tyle długo żeby można było opisać jak wygląda zmienność tych obszarów w trakcie cyklu aktywności, to będzie można mówić, że sonda zacznie odkrywać tajemnice wieloletniej aktywności Słońca. 

This year, another mission – Solar Orbiter – began; what will be its significance in the conducted research?

Solar Orbiter will bring results only after several years of operation, although it is designed to observe the Sun from the beginning of its presence on the orbit and to record and track short-term phenomena (including flares, CMEs). However, it must be emphasized that the probes are complementary to each other. Compared to the Parker Solar Probe, the Solar Orbiter will observe the Sun from a distance, using telescopes. At the time of the closest approximation, it will be approx. 40 million kilometres, i.e. within Mercury’s orbit. However, not as extremely close as in the case of the Parker Solar Probe. Thanks to the Solar Orbiter telescopes, the Sun will be very closely observed, and the particles and magnetic fields will be analysed by detectors at the place where the probe will be. This complementarity of the probes will give a lot of data that will allow us to uncover the secrets of active, short-lived phenomena. After several years of operation, Solar Orbiter, which will be lifted above the ecliptic with each orbit around the Sun, will begin to study the Sun’s poles. These are the areas that we have not seen well until now. They can be seen from Earth’s orbit with a foreshortened perspective. These areas are critical in terms of building models of long-term solar activity. The most important processes take place there from the point of view of long-term evolution of magnetic fields in time scales longer than the 11-year cycle. This will be a big step in understanding what is happening with magnetic fields. These observations will to some extent help us understand the phenomena over the years, e.g. whether the concept that there will be a period of suppression of activity, and thus possible cooling, is real.

What contribution do Polish researchers have to the study of the Sun?

Polish scientists working on individual instruments, such as the Spice UV spectrometer, are involved in the Solar Orbiter mission. The head of the consortium working on the spectrometer is Dr Andrzej Fludra, who received his PhD from the University of Wrocław and is currently working in the United Kingdom. The construction of the Metis coronagraph was joined by Prof. Arkadiusz Berlicki, heliophysicist of the Astronomical Institute at the Faculty of Physics and Astronomy of the University of Wrocław. However, we have the largest contribution in the STIX instrument, in which a big group (about 20 people) of engineers and scientists from the Space Research Centre of the Polish Academy of Sciences was involved. This is an X-ray telescope, with a unique design. The STIX telescope is used to observe solar flares and X-ray emissions from the Sun. The magnetically active Sun is also a star that emits a lot of X-rays. Poland participated in both the design and construction phase of this instrument. Our contribution before the launch of the probe was at a level of 20%, the second most important, just after the contribution of Swiss scientists who manage the experiment. Polish scientists from the Space Research Centre and the University of Wrocław are also currently involved in the space measurement phase as well as data analysis. This is the largest group of scientists among all countries involved in the STIX experiment. Impressive. It is rare for Poland to be involved in such a pioneering space mission. The Parker Solar Probe and Solar Orbiter are both extraordinary projects.

Polska miała udział zarówno w fazie opracowania konstrukcji jak i budowy tego instrumentu. Nasz udział przed wystrzeleniem sondy był na poziomie 20 proc., drugi co do znaczenia, zaraz po udziale szwajcarskich naukowców, którzy zarządzają eksperymentem. Polscy naukowcy z Centrum Badań Kosmicznych i Uniwersytetu Wrocławskiego są także zaangażowani obecnie w fazie pomiarów w kosmosie jak i w analizę danych. To największa grupa naukowców spośród wszystkich krajów zaangażowanych w eksperyment STIX. Imponujące. Rzadko się bowiem zdarza, aby Polska była zaangażowana w tak pionierską misję kosmiczną. Zarówno Parker Solar Probe jak i Solar Orbiter to wyjątkowe przedsięwzięcia.

Will 2020 bring interesting astronomical phenomena? What special views can be seen in the sky?

This year we will observe a gradual increase in the activity of the Sun, which is clearly going up. There probably won’t be an opportunity to see an aurora in Poland yet, but it will probably happen next year. This phenomenon is worth waiting for.

At the end of the year, a total solar eclipse will be observed, mainly from South America. On 14 December 2020 the Moon will obscure the Sun over the Pacific. Its shadow will cross the southern tip of South America and in Argentina, visible for a maximum of more than 2 minutes. In the southern hemisphere this is the middle of summer so the weather will be favourable for observations.

For those who will stay in Poland, however, the most interesting phenomenon in the sky will be the conjunction of Jupiter and Saturn – these planets will line up quite close to the Sun. This will occur on 21 December this year. The planets will be in the sky about 6 arcminutes. It’s very close. We probably won’t be able to distinguish between Jupiter and Saturn with the naked eye, but with binoculars or a small telescope, you will be able to see Saturn with rings and Jupiter with four Galilean moons together. It is going to be an unforgettable and unique view! I recommend It!

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