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What's the link between cosmic rays and climate change?

What the science says...

Select a level... Basic Intermediate Advanced

Cosmic ray counts have increased over the past 50 years, so if they do influence global temperatures, they are having a cooling effect.

Climate Myth...

It's cosmic rays

"When the Sun is active, its magnetic field is better at shielding us against the cosmic rays coming from outer space, before they reach our planet. By regulating the Earth’s cloud cover, the Sun can turn the temperature up and down. ... As the Sun’s magnetism doubled in strength during the 20th century, this natural mechanism may be responsible for a large part of global warming seen then."  (Henrik Svensmark)

At a glance

Space may often be regarded as dark, cold, empty and lifeless but there is plenty going on out there, including the streams of high-energy particles that whizz around at close to the speed of light. These are galactic cosmic rays, discovered by Austrian-American physicist Victor Hess in 1912. Galactic cosmic rays is a catch-all term that includes high-energy particles with sources ranging from the Sun to remnants of ancient supernovae – exploded stars – in other galaxies.

When cosmic rays hit the top of our atmosphere, a highly crowded environment compared to deep space, they interact with the atoms up there producing showers of charged particles known as ions. The ions then head on down towards the surface, where they make up just over ten percent of our typical yearly radiation dose. That's approximately equivalent to three chest x-rays.

The Solar wind protects Earth from cosmic rays and Earth's strong magnetic field in turn shields us from both. In this respect we are fortunate: if you want to find out what happens to a planet that has lost its strong magnetic field, go and take a look at Mars. As a result of these planetary defences, the amount of cosmic rays reaching the lower atmosphere and surface of Earth is minimised.

Direct recording of the cosmic ray flux has been possible since the beginning of the satellite era, since the satellites can carry particle detectors. We therefore have over a half-century worth of data on the changes in the intensity of the flux.

The idea that changes in the cosmic ray flux could drive the observed global warming has a small but determined number of fans. In short, their hypothesis suggests that the ions produced by cosmic rays can 'seed' clouds. That means more cloudiness - and clouds reflect sunlight, reducing the energy reaching Earth's surface. So, it imagines, if there are fewer cosmic rays reaching Earth, there will be fewer clouds, more sunlight reaching the Earth's surface, and thus more global warming. In a sense, this is a variant of the “It's the Sun” argument, because the cosmic ray flux falls when the Sun is in the active phase of its 11-year sunspot cycle and the Solar wind is typically stronger.

In 2017, the Cosmics Leaving Outdoor Droplets (CLOUD) experiment reported in. It had been created to test the link between cosmic rays and climate and was specifically looking for any connection between ions resulting from cosmic rays and cloud-seeding. The CLOUD experiment succeeded in unlocking many of the mysteries of cloud formation and growth in our atmosphere. That greatly improved our understanding of human influences on climate. In particular the study concluded that the effect of changes in cosmic ray flux intensity on the cloud condensation process is small. To quote its authors, it is, "unlikely to be comparable to the effect of large variations in natural primary aerosol emissions" - things like volcanic eruptions, wildfires and so on. So no, cosmic rays do not have much of an effect at all.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!

Further details

It was at one time hypothesised that galactic cosmic rays (GCRs) may play a part in helping form clouds. A leading proponent of this idea was Danish scientist Henrik Svensmark. If this hypothesis were correct, an increase in the GCR flux, creating an increase in cloud condensation nuclei, would lead to more cloud cover in our lower atmosphere, reflecting more sunlight and resulting in a global cooling effect. Conversely, a decrease in GCR flux would lead to a reduction in cloudiness, warming the planet by letting more sunlight through.

People look at new hypotheses in order to test them. In order to calculate the maximum possible role of GCRs in recent warming, global temperatures have been compared to variations in the GCR flux, as measured by particle detectors aboard satellites and by neutron monitors at the Earth's surface. We'll take a look at some of these studies, for there are many, mostly reaching the same conclusion but with improvements in methodology through time, as always tends to occur in scientific research.

A 2003 paper observed that while there was some correlation between GCR levels and temperature prior to 1970, the correlation breaks down sharply after that point. The analysis concluded that "between 1970 and 1985 the cosmic ray flux, although still behaving similarly to the temperature, in fact lags it and cannot be the cause of its rise. Thus changes in the cosmic ray flux cannot be responsible for more than 15% of the temperature increase" (Krivova & Solanki 2003).

Krivova & Solanki (2003) 

Figure 1: Reconstructed cosmic radiation (solid line before 1952) and directly observed cosmic radiation (solid line after 1952) compared to global temperature (dotted line). All curves have been smoothed by an 11 year running mean (Krivova & Solanki 2003).

Another analysis from the 2000s scrutinises the link between GCRs and cloud cover and finds several discrepancies. As GCR flux shows greater variation in magnitude in high latitudes, one would expect larger changes in cloud cover in polar regions. This, the authors found, was not observed. They also examined the aftermath of the nuclear reactor accident at Chernobyl: the thinking was that if the GCR hypothesis was correct then since the Chernobyl site was a strong source of ionising radiation, some effect on cloud formation might be expected. They found none (Sloan & Wolfendale 2008).

The chance to soundly test the Svensmark hypothesis came up again in a particularly extended Solar minimum (between solar cycles 23 and 24, 2008-2010). This minimum was associated with a record high level of GCR flux, but at the same time, there was a record low level of cloudiness in the lower atmosphere – the bottom ~10 kilometres of the atmosphere where most of the weather occurs. If the GCR/cloud seeding idea was correct, the reverse should have been the case (Agee et al. 2012; fig. 2). Also in 2012, an important review paper, covering the past 35 years of research, concluded, “it is clear that there is no robust evidence of a widespread link between the cosmic ray flux and clouds.” (Laken et al. 2012).

GCR vs. Temp

Figure 2: Annual average GCR counts per minute (blue - note that numbers decrease going up the left vertical axis, because lower GCRs should mean higher temperatures) from the Neutron Monitor Database vs. annual average global surface temperature (red, right vertical axis) from NOAA NCDC, both with second order polynomial fits.

More recently, the Cosmics Leaving Outdoor Droplets (CLOUD) experiment, created to systematically test the link between GCRs and climate, reported in. It had been specifically looking for any connection between ions resulting from GCRs and aerosol nucleation and thus cloud condensation nuclei and cloud formation. The CLOUD experiment succeeded in unlocking many of the mysteries of nucleation and cloud growth in our atmosphere, greatly improving our understanding of human influences on climate. In particular the study concluded that the effect of changes in GCR flux intensity on the cloud condensation process is small and “unlikely to be comparable to the effect of large variations in natural primary aerosol emissions” - things like volcanic eruptions, wildfires etc (Gordon et al. 2017).

This story illustrates nicely how science proceeds. Someone thinks up a hypothesis and it is repeatedly put to the test and is found to be wanting. In turn that leads to further research and important discoveries, providing progressively better understanding into the details of how certain processes work – atmospheric ones in this case. In recent years, Svensmark has been associated with the likes of the Global Warming Policy Foundation, the Heartland Institute and other such organisations who prefer their own version of reality (details at DeSmog). Meanwhile, the science has moved on and left him behind.

Update June 17, 2023 - Based on feedback received, added a concluding paragraph to the at-a-glance section.

Last updated on 18 June 2023 by John Mason. View Archives

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Further reading

A team of scientists from 17 countries have found the most likely origin of galactic cosmic rays - the centres of distant galaxies (Active Galactic Nuclei) powered by supermassive black holes. This discovery is not particularly pertinent to the global warming debate but it is cool :-)

Further viewing

This video published on Nov. 17, 2019 by "Have a think" provides some more and current explanations of why GCRs do not play a role in current global warming.



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Comments 101 to 122 out of 122:


    He's baackk, 

    H. Svensmark, M. B. Enghoff, N. J. Shaviv, J. Svensmark. Increased ionization supports growth of aerosols into cloud condensation nuclei. Nature Communications, 2017; 8 (1) DOI: 10.1038/s41467-017-02082-2

    December 19, 2017
    Technical University of Denmark
    The study reveals how atmospheric ions, produced by the energetic cosmic rays raining down through the atmosphere, helps the growth and formation of cloud condensation nuclei — the seeds necessary for forming clouds in the atmosphere.


    Henrik Svensmark confidently broadcasts and hundreds of astroturfers are busy spreading the word: "Finally we have the last piece of the puzzle explaining how particles from space affect climate on Earth. It gives an understanding of how changes caused by Solar activity or by super nova activity can change climate." says Henrik Svensmark, from DTU Space at the Technical University of Denmark, lead author of the study. Co-authors are senior researcher Martin Bødker Enghoff (DTU Space), Professor Nir Shaviv (Hebrew University of Jerusalem), and Jacob Svensmark, (University of Copenhagen).


    Links to serious critiques of this paper and ther authors claims would be appreciated.

  2. First thing I noticed on the link: a "LIA" period that is now considered to have lasted from 1300 to 1900 AD. That's going to impair those medival warm periods that fell right in the middle of it...

    Seems it's just more recycling of the same stuff but hard to tell from the sciencedaily because that's not the paper itself. More digging in order. AFAIK, CERN has not rescinded their take on their experimental results, which weren't very supportive of the hypothesis.

  3. To his credit, Watts in his WTFUWT post about Svensmark's "new" claims solicited Leif Svalgaard's opinion. Here is what Watts posted as the reply from Svalgaard:
    "TSI over a solar cycle causes a variation of 0.05-0.10 degrees C. If GCRs as per Svensmark has 5-7 times the effect of TSI, that would translate to a temperature variation of 0.35-0.50 C over a cycle, which is simply not observed, hence the paper can be dismissed out of hand."

    Danish theorist’s latest paper overstates the effects of solar activity in climate change, critics say.
    Tim Wallace reports.

    No, Supernovae Aren’t Changing Earth’s Climate
    Ryan F. Mandelbaum


    Galactic cosmic rays

  5. This seems to be the main SkS page on galactic cosmic rays, reachable via I like the way the advanced version highlights the slim chance of new particles reaching the necessary size (about 50nm?) to become cloud condensation nuclei (and that the basic version just reiterates that there's no historical connection).  There are other rather outdated pages that could be linked here:

    It does look like the CERN CLOUD experiments are producing unexpected and useful results, possibly finally reducing the uncertainty range in the effect of anthropogenic aerosols, but are pretty conclusive that cosmic rays have a very small effect.

    One of the most recent CERN results (Gordon et al, 2017) concludes 'Our model suggests that the effect of changes in cosmic ray intensity on CCN is small and unlikely to be comparable to the effect of large variations in natural primary aerosol emissions.' and this seems consistent with other methods finding <1% of cloud condensation nuclei are related to cosmic rays.

    However, there is some good news I've seen contrarians pick up from CLOUD studies: although present cloud effects are dominated by anthropogenic sulphates (potentiated by ammonia?), in the pre-industrial atmosphere, terpenes and pinenes and other natural VOCs had a role seeding cooling clouds.  This potential constraint on aerosol effects could reduce upper limits on ECS - one of the researchers is quoted as saying "the highest values become improbable".  I'm not clear if this is ECS > 4°C, say, or whether a reduced uncertainty has fed into recent attempts at 'quantifying our Faustian bargain' of reducing sulphate pollution.

  6. In his recent book, Rex J. Fleming asserts that "CO2 has no impact on climate change", or, as he summarizes on his website:

    There are now over a dozen books available on that point out the various fallacies of the CO2 climate theory – but none of these have zeroed in on the heart of the issue – the failure of the Schwarzschild radiation integrations to maintain the CO2 longwave radiation intensity achieved in the surface warming by H2O and CO2. The resultant Planck radiation intensity is severely depleted in the upper atmosphere. The result is the CO2 molecules merely pass their remaining small residual heat to space un-impeded. CO2 has no impact on climate change.

    This claim seems to contradict some basic physics.

    Is Fleming correct that the "failure of the Schwarzschild radiation integrations to maintain the CO2 longwave radiation intensity" means that "CO2 has no impact on climate change"?

  7. People with half-baked ideas on physics that they learnt of wikipedia confusing other people who would desparately like to be comforted about their predjudices. This is nonsense and directly contradicted by observations. If observations contradict what someone would expect from accepted theory, especially if not formally taught, then chances are it is the persons understanding of the theory not the theory itself that is wrong. Books on Amazon tell you how many suckers are out there. Dozens of peer-reviewed papers would be another story.

  8. Aldaron @106,

    The Schwarschild equation calculates the amount of radiation transmitted through a medium (like the Earth's atmosphere) when there are substances absorbing/emitting that radiation (as do greenhouse gases). The Schwarschild equation tells us that we will have global warming if we increase the GHG concentrations as the more GHG the higher the emission-into-space altitude and the higher you go (in the troposphere) the colder it gets so the less radiation is emitted into space.

    Without reading Fleming's book, the quote you provide seems to be saying just that. The surface is warmed by back radiation (from CO2 & H2O) so an enhanced IR flux travels up from the surface through the atmosphere being absorbed/emitted as it goes. But as it rises through the troposphere, the temperature drops. Thus, according to the Schwarzchild equation, there will indeed be a "failure ...  to maintain the CO2 longwave radiation intensity achieved in the surface warming." Thus when the density of GHG increases and the altitude at which this IR flux is transmitted into space rises to higher and colder altitudes, the flux out to space which cools the planet will be of yet lower 'intensity'. Less cooling of the planet so more global warming.

    Fleming's book appears a recent publication (June 2019) and a whole 144 pages long covering from 'Chapter 2 - Creation of the Universe' to "Chapter 14 - Future Research on Climate and Energy Issues'. It is either very small writing or a very compact theory being presented. But, hey, why should climate be so complex anyway?

    There is also this very day a Heatland pod-caste featuring this same Fleming (25 mins long) than may give some inkling of what is proposed but I couldn't cope with the first 20 seconds that simply comprised lift music.

    And I note Google have a reviewable entry of the book so may have a go at reading relevant sections over a cup of tea some time.

    But until then my judgement is unchanged. Fleming has misunderstood Schwarzchild.

  9. Aldaron @106,

    Tea time has come and gone so I can report back. Yet this report remains incomplete even after two cups.

    My peek inside Flemings book shows he is doing some big calculations using HITRAN data which appears to confirm the AGW impact of CO2. But then through his analysis somehow adopting a rogue coefficient of his own contrivance, Fleming manages to produce a fundamentally different result. Yet Fleming fails to explain this situation and resorts to an incoherent explanation. Indeed, the whole tends to incoherence.
    Note that your quote @106 (from Fleming's website) doesn't bear much relation to what his book says.

    In his book, the Summary of Chapter 11 pp80-82 tells us rather incoherently that if you use a larger deffusion coefficient (of unknown origin) on the HITRAN data, you can calculate the effective level of transparency (this the altitude where the CO2 is radiating out into space and so cooling the planet) as being up at an altitude of 16km. That  is up in the stratosphere while the usual analysis, as Fleming also shows, would be lower at 9km in the troposphere. He doesn't say, but were this higher level  true the impact of adding CO2 to the atmosphere (CO2 is well mixed up to 50km) would actually be be to cool the planet.
    (For the record, a small part of the 15 micron CO2 absorption band does already operate up into the stratosphere and that small part will become bigger with increasing CO2. But the net effect will remain warming as there is much much more of the CO2 absorption bands still operating in the troposphere and they warm the planet with increasing CO2.)

    Fleming's explanation for his finding of zero AGW effect is entirely incoherent. He tells us the temperature-with-altitude effect is "very strong" and also "the diffuse radiation intensity depletes rapidly over vertical distance" but that also the CO2 temperature-with-altitude effect is "quite small", as is the CO2-effect relative to the whole IR spectrum analysed (1 micron to 30 micron). As I say, this is incoherent and shows no understanding of the AGW mechanism. Plus, even if this explanation could be understood, these reasons are not in any way quantified to demonstrate their significance.

    While peeking into Fleming's book, I also noticed on p82 reference 6 - R.J. Fleming, (2018) "An updated review about carbon dioxide and climate change", Environmental Earth Sciences, vol. 77, pp1-13.
    As specifically pointed out by Gavin Schmidt @ RealClimate, this is not a proper peer-reviewed paper as the journal doesn't cover climatology (it covers Geology, Hydrology/Water Resources, Geochemistry, Environmental Science and Engineering, Terrestrial Pollution, Biogeosciences) and shouldn't be accepting a paper so far beyond its speciality.

    Now, despite the grand revalation of Fleming's paper allegedly overturning the entirety of clomatology, it has received zero citation since publication in March 2018. I say that as currently Google Scholar lists just four citations. Two are by Fleming himself and of the other two, both are obvious mistakes. One does not cite the paper at all. The other cites it for the exact opposite of Fleming's thesis, its opening line being - "It has been scientifically well established that carbon dioxide (CO2), a major greenhouse gas, is the prime reason for the climate change and global warming phenomena in recent decades" (Fleming 2018)
    Fleming (2018) is paywalled and I took a whole tea break looking for a full version on-line and here it is in PDF. I shall have a read in due course.

  10. Aldaron @106,

    First a correction. I said @109 that one of the citations of Fleming (2018) was an error as it didn't cite Fleming at all. That was wrong. I was looking at the wrong PDF. Vuori (2019) does cite Fleming (2018) but cites it as being an exemplar of climate change denial.

    And I have 'read' Fleming (2019) but not from start-to-finish as it is packed full of denialist nonsense as well as being, shall we say, less than coherent. (For instance in Section 3 it kicks off citing a reference which insists global warming is in the long term due to the weight of the atmosphere and then one of the GWPF 'experts' Ian Plimer who's reliability is more a joke than questionable.)

    Fleming (2018) gives more detail of method than Fleming (2019) while being consistent with Fleming (2019) in demonstrating a failure to understand the mechanisms of GHG operation. Where it differs from Fleming (2019) is in not carrying out that final analysis of Fleming (2019) which used that unusual deffusion coefficient. Thus, unlike Fleming (2019), his main finding (that w.r.t. CO2 the atmosphere is effectively transperent to IR in-and-above the upper troposphere) is in tune with everybody else but his interpretation of this (that CO2 "contributes low level heating and allows upper level cooling for a zero net effect") is so-much gibberish.

  11. i respectfully disagree. 

    1. Only 2% of the atmosphere is greenhouse gases, only 3.62% of that is CO2 and only 3.4% of CO2 is due to human activity
    2. CO2 lags temperature changes by 800 years
    3. Sea levels have already been rising for the past 8000 years
    4. Climate change model's predictions have all been overestimates
    5. There has been no global warming for 18 years
    6. There has been no increase in the frequency of storms since 1954
    7. There has been no increase in the frequency or severity of droughts in the US
    8. Warming in the past (before human history) has been far more drastic in the past indicating that current warming is not human caused

    check these infographics to understand more,




    i'd really to ask someone to prove me wrong. 

    human made global warming isn't a huge deal, and there are bigger threats than this. 


    [DB]  Pretty much every point you make is disproven on other threads here. Use the Search function to find a more appropriate thread.  After you read them and the comment threads attached, if you still have concerns, place those concerns there, not here.

    Please stay on-topic.

  12. unknownwallet @111,

    (I should point out that you do not address the bogus cosmic ray theory which is the actual subject of this comment thread.)

    You say "i'd really to ask someone to prove me wrong" so let's kick off with your statement number one (which is also illustrated top left in the collection of graphics in your third URL).

    By volume, the percentage of water vapour in the atmosphere is 0.4% (and roughly half that by weight), thus much lower than the 2% value you present. In a dry atmopshere, today's CO2 levels top 400ppm(v) or 0.04% (0.06% by weight). Again this is greatly different to your value of (0.02 x 0.0362 =) 0.072%.

    Today's CO2 levels are (1 - 280/400 =) 30% anthropogenic thus 0.012% of the total atmosphere by volume (0.018% by weight) where as you say 3.4% of CO2 is due to human activity and thus 0.0025% of the atmosphere.

    (I should also mention the graphic below top left on your third URL which gives different values again 1% for all GHGs, of which 4% CO2, of which 4% is anthropogenic.)

    The raw volumes/weights of GHGs in the atmosphere is not in a very good gauge of their impact on the climate. Water vapour, for instance, is only present at the levels we see because the long-lived GHGs (which are predominantly CO2) It is long-lived GHGs that raise global temperatures and it is only this increased temperature that to allow the atmosphere to hold such levels of water vapour. And despite there being ten-times-more water vapour (by volume) than CO2 in today's atmosphere, its contribution in boosting the GH-effect is far less than 10x (even when cloud is factored in).

    The one value you provide that is entirely a mystery but also fundamental to your argument is the percent of CO2 - "only 3.4% of CO2 is due to human activity." Where does that 3.4% value come from?

  13. Please check out the new video in the further viewing section above. It was published on Nov. 17, 2019 by "Have a think" and provides some more and current explanations of why GCRs do not play a role in current global warming.

  14. Does it matter that the earth's magnetic field is weakening? If the Earth's magnetic field is weakening, then the impact of cosmic rays should be stronger over time. If the argument is that cosmic rays should have a cooling effect, then it should have a greater effect over time. 

  15. jmh530, the best available evidence we have is that there is no direct linkage between the sun’s output and cosmic rays impacting the Earth’s climate. Now that’s a broad statement, but let’s examine some more in-depth evidence on those individual components.

    Scientists use a metric called Total Solar Irradiance (TSI) to measure the changes in output of the energy the Earth receives from the Sun. And TSI, as one would expect given the meaning behind its acronym, incorporates the 11-year solar cycle AND solar flares/storms.

    The reality is, over the past 4 decades of significant global warming, the net energy forcing the Earth receives from the Sun had been negative. As in, the Earth should be cooling, not warming, if it was the Sun.

    It's not the sun

    The scientists at CERN designed an experiment called CLOUD to evaluate the potential impacts of cosmic rays on clouds and cloud nucleation (Cloud Condensing Nuclei = CCN).

    Per CLOUD director Kirkby:

    "At the present time we can not say whether cosmic rays affect the climate."

    Looking at the results of CLOUD, if cosmic rays were a significant factor in affecting our climate, the Earth should have been cooling, not warming. Instead 8 of the warmest 10 years have all occurred in the most recent 10 years.

    Erlykin et al 2013 - A review of the relevance of the ‘CLOUD’ results and other recent observations to the possible effect of cosmic rays on the terrestrial climate

    The problem of the contribution of cosmic rays to climate change is a continuing one and one of importance. In principle, at least, the recent results from the CLOUD project at CERN provide information about the role of ionizing particles in ’sensitizing’ atmospheric aerosols which might, later, give rise to cloud droplets. Our analysis shows that, although important in cloud physics the results do not lead to the conclusion that cosmic rays affect atmospheric clouds significantly, at least if H2SO4 is the dominant source of aerosols in the atmosphere. An analysis of the very recent studies of stratospheric aerosol changes following a giant solar energetic particles event shows a similar negligible effect. Recent measurements of the cosmic ray intensity show that a former decrease with time has been reversed. Thus, even if cosmic rays enhanced cloud production, there would be a small global cooling, not warming.”

    Modern CCN are pretty much insensitive to cosmic rays and changes in TSI from the Sun, compared to the very much larger anthropgenic and natural contributions (volcanoes, oceanic oscillations and wildfires):

    "New particle formation in the atmosphere is the process by which gas molecules collide and stick together to form atmospheric aerosol particles. Aerosols act as seeds for cloud droplets, so the concentration of aerosols in the atmosphere affects the properties of clouds. It is important to understand how aerosols affect clouds because they reflect a lot of incoming solar radiation away from Earth's surface, so changes in cloud properties can affect the climate.

    Before the Industrial Revolution, aerosol concentrations were significantly lower than they are today. In this article, we show using global model simulations that new particle formation was a more important mechanism for aerosol production than it is now. We also study the importance of gases emitted by vegetation, and of atmospheric ions made by radon gas or cosmic rays, in preindustrial aerosol formation.

    We find that the contribution of ions and vegetation to new particle formation was also greater in the preindustrial period than it is today.

    However, the effect on particle formation of variations in ion concentration due to changes in the intensity of cosmic rays reaching Earth was small."


    " cycle variations of ion concentration lead to a maximum 1% variation of CCN0.2% concentrations. This is insignificant on an 11 year timescale compared with fluctuations due to, for example, the El Nino-Southern Oscillation, variations in wildfires, or volcanoes."

    Gordon et al 2017 - Causes and importance of new particle formation in the present-day and preindustrial atmospheres

    And the coup de grace for cosmic rays, being proven to unable to significantly affect clouds and climate, is that CCN respond too weakly to changes in Galactic Cosmic Rays to yield a significant influence on clouds and climate.

    Pierce 2017 - Cosmic rays, aerosols, clouds, and climate: Recent findings from the CLOUD experiment

    Scientist Richard Alley pretty much killed the cosmic ray hypothesis here (the relevant part of the lecture starts at 42:00)

    "We had a big cosmic ray signal, and the climate ignores it. And it is just about that simple! These cosmic rays didn’t do enough that you can see it, so it’s a fine-tuning knob at best."

    To recap, the Laschamp excursion (the strongest cosmic ray event in the past 40,000 years) hammered climate for 2,550 years about 40,000 years ago. The flux of beryllium-10 produced by cosmic rays greatly increased as the Earth’s magnetic field weakened by 90%.

    Climate ignored it.

    Here is the chart he’s referring to, showing how the flux of beryllium-10 produced by cosmic rays greatly increased as the Earth’s magnetic field weakened by 90% about 40,000 years ago.

    It's not cosmic rays

    From the AR5, WG1, Chapter 7, p. 573:

    "Cosmic rays enhance new particle formation in the free troposphere, but the effect on the concentration of cloud condensation nuclei is too weak to have any detectable climatic influence during a solar cycle or over the last century (medium evidence, high agreement). No robust association between changes in cosmic rays and cloudiness has been identified. In the event that such an association existed, a mechanism other than cosmic ray-induced nucleation of new aerosol particles would be needed to explain it. {7.4.6}"

  16. Hi
    Do you know if this new discovery related to the "iron cosmic rays" in any way alters your refutations of the Henrik Svensmark hypothesis? Thanks.

    - AMS reveals properties of iron cosmic rays;
    Ironing Out Cosmic Rays;
    Properties of Iron Primary Cosmic Rays: Results from the Alpha Magnetic Spectrometer.


    [BL] This appears to be your first post here. Welcome to Skeptical Science!  There is an immense amount of reference material discussed here and it can be a bit difficult at first to find an answer to your questions.  That's why we recommend that Newcomers, Start Here and then learn The Big Picture.

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  17. If you look at the advanced tab, you see the steps that must be fufilled for GCR to influence climate. While it is great that advances are being made in understanding GCRs, I dont see how those discoveries impact in any way on creating a climate impact. The empirical evidence for correlation between GCR and cloud formation remains elusive.

  18. yurivs @116,

    The research you cite concerns the classification of cosmic rays that have been known about for decades. It does not alter understanding of the cosmic rays arriving at Earth, rather points towards whee they come from. As scaddenp @117 alludes to, Svenmark has been barking up the wrong tree for decades now in a hopless journey to prove that black is white.

  19. Please note: the basic version of this rebuttal has been updated on June 4, 2023 and now includes an "at a glance“ section at the top. To learn more about these updates and how you can help with evaluating their effectiveness, please check out the accompanying blog post @

    Thanks - the Skeptical Science Team.

  20. Can someone here can comment on a more recent Svensmark paper that seems to butress his agrgument? 11 Oct 2021

    On the other hand here is a newer paper with a 40 year data base:

    Thanks in advance to someone more knowledgeable than I am.


    [PS] Links activated. Please learn how to do this yourself in the comment editor.

  21. I interpret his 2021 paper to augment and solidify the fact that man made greenhouse gases are responsible for all of the increase in global temperature over the last half century. As I understand his argument, Increases in coronal mass injections cause more warming of the Earth. But the Sun has become less active over the last half century while the global temperatures increased and CO2 concentration increased . The  the graph in an earlier comment above is also in
    Svensmark's work would predict lower temperatures, but global temperatures are in fact higher.


    [RH] Link shortened

  22. sailingfree @120/121,
    The H. Svensmark input into AGW science has been in general seen as entirely overblown unless you are in denial about AGW when the idea that the sun plays a much bigger role than the climatology shows is usually seen as supportive of their denialism.

    Svensmark first published a cosmic ray climate effect back in 1997 demonstrating a remarkable fit between cosmic rays and global cloud cover. The fit proved to be spurious while experiment has demonstrated the causal link between cosmic rays and cloud formation to be very very weak. Undeterred by these setbacks, Svensmark has since been examining the detail of the cosmic ray/cloudiness relationship in an attempt to show there was a climatic effect after all.

    Part of this analysis by Svensmark homed-in on Forbush Decreases, a phenomenon identified back in the mid-1900s and today catalogued at an average rate of over 100 events per year. A relationship bewteen these Forbush Decreases and changes in cloud had been observed back in the 1990s.

    Svenmark first published on this phenomenon back in 2009. They used the most energetic Forbush Decreases (just 26 over 21 years) to produce a correlation between peak cloudiness and the Forbush Decrease strength (Fig 2- not entirely convincingly) and plotting the averages of cosmic ray evolution and average cloudiness evolution for the five most energetic Forbush Decrease events (Fig 1) although the reason for showing the averaging of these five alone is not evident to me in this paper.

    Svensmark et al (2021) which you ask about is simply Svensmark et al (2009) but using a correlation with the CERES radiation data. The CERES data restricts analysis to post-2000 events and now only the 13 most energetic events are analysed for the correlation (fig 2) with event evolutions averaged from (again) the five strongest events (fig 1), this apparently because there is too much "dominant meteorological noise" if more events are included, although I'm not sure that squares up with the effect being climactically significant.

    Of course, with the sun less active since SunSpotCycle 23, and thus presumably the cosmic rays increasing cloudiness which cools the climate, this would suggest that Svensmark's work would be implying amplification of the role of AGW rather than a diminution which denialists hope for. But such understanding may be a bit too involved for denialists to grasp.

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