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Cosmic rays fall cosmically behind humans in explaining global warming

Posted on 12 November 2013 by dana1981

For climate skeptics trying to find an alternative explanation for the global warming that's occurred over the past century, the sun and galactic cosmic rays have become a popular hypothesis. However, several recent scientific papers have effectively put the final nail in the cosmic rays-global warming coffin.

Galactic cosmic rays
are high energy particles originating from outside our solar system. Henrik Svensmark of the Danish National Space Institute is the main proponent of the hypothesis linking them to global climate change. The hypothesis goes like this:

1) Cosmic rays may be able to seed cloud formation.
2) If so, fewer cosmic rays reaching Earth means less cloud formation.
3) Fewer clouds reflecting sunlight means more solar radiation reaching the Earth's surface, and thus warming.

The sun's magnetic field deflects galactic cosmic rays, so if the sun is in a phase of high activity with a strong magnetic field, fewer cosmic rays will reach Earth. Hence if this hypothesis is correct, galactic cosmic rays will act to amplify the solar influence on the global climate, whether it be a cooling effect from low solar activity or warming from high solar activity.

This is a relatively new and interesting hypothesis, so it's become popular amongst climate contrarians as an alternative explanation to human-caused global warming. However, it's also been the subject of extensive scientific research over the past few years, and the hypothesis simply has not held up to scrutiny.

First, there's the obvious fact that cosmic rays cannot explain the recent global warming because solar activity and the amount of cosmic rays reaching the Earth's surface have remained flat on average over the past 60 years. The sun and cosmic rays could only be causing global warming if there were a long-term upward trend in solar activity and downward trend in cosmic rays reaching Earth. In fact, the number of cosmic rays reaching Earth has increased since 1990, and reached record levels in 2009 (one of the hottest years on record).

temp vs. cosmic rays

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.

A paper published in the journal Meteorology and Atmospheric Physics this August noted,

"Recent measurements of the cosmic ray intensity show that … even if cosmic rays enhanced cloud production, there would be a small global cooling, not warming."

Two of the authors of that paper (Sloan & Wolfendale) have also just published another cosmic ray research paper in Environmental Research Letters, finding that the contribution of solar activity and galactic cosmic rays (combined) to global warming is "less than 10% of the warming seen in the twentieth century."

Sloan & Wolfendale also examine the influence of cosmic rays on the climate over the past billion years in another new paper published in the journal New Astronomy. They find that changes in the galactic cosmic ray intensity are too small to account for significant climate changes on Earth. This was also the conclusion of a paper published this May in The Astrophysical Journal.

In another paper just recently published in Environmental Research Letters, Rasmus Benestad of The Norwegian Meteorological Institute compares measured changes in the amount of cosmic rays reaching Earth to changes in temperature, precipitation, and barometric pressure measurements. Benestad finds no statistical evidence that cosmic rays can explain the recent global warming.

Finally, a paper published last month in Geophysical Research Letters compared measurements of cosmic rays and cloud cover changes, and found no detectable connection between the two. This study is consistent with many previous papers finding that cosmic rays are not effective at seeding clouds.  Likewise, in the CERN CLOUD experiments, Almeida et al. (2013) found

"ionising radiation such as the cosmic radiation that bombards the atmosphere from space has negligible influence on the formation rates of these particular aerosols [that form clouds]"

Thus every step in the galactic cosmic ray-climate hypothesis is fraught with problems. Evidence suggests that cosmic rays are not effective at seeding clouds. Solar activity has been flat, and even slightly downwards over the past few decades. Galactic cosmic ray flux on Earth has been flat, even slightly upwards over the past few decades. 2009, which saw a record number of cosmic rays reaching Earth (meaning it should have been cold), was the 5th-hottest year on record at the time.

This failed hypothesis offers a stark contrast to the overwhelming consensus that our greenhouse gas emissions are driving warming. The latter is supported by solid, well-understood fundamental physics. We know that increasing the greenhouse effect causes more energy to be trapped on Earth, and that energy has to go somewhere. The observed pattern of warming is precisely what we expect to see from an increased greenhouse effect, for example with the 'fingerprint' of a cooling upper atmosphere due to more heat being trapped in the lower atmosphere.

Click here to read the rest

Note: this post has been incorporated into the Advanced rebuttal to the myth "it's cosmic rays"

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Comments 1 to 16:

  1. Re (3) of the hypothesis (fewer clouds will warm the earth) - is that true?What's the latest on the relationship between cloud cover changes and global temperature?I was under the impression that clouds-keep-heat-in-at-night and clouds-reflect-sunlight basically cancelled each other out?
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  2. suckfish@1,

    Your assessment is simplistic and incorrect.

    "clouds-keep-heat" (not just "at-night" but 24h) when they absorb ountgoing IR. Such property is attributed to high "Cirrus" clouds. Their effect is warming.

    Other clouds, like low "Stratus" clould, do not a bsorb IR but they are very good at scattering the incoming solar radiation (with that respect they act as if they increased the Earth albedo), that's why the "look dark" from below. Their effect is cooling.

    But on global average, the "cooling clouds win", i.e. stratus effect outweigh the effect cirrus effect. So, if the increased CR results in more cloud seeding, the net effect is cooling, assuming on average all types of clouds are seeded uniformely. I think that's the assumption of this article.

    Of course, verious "sceptics" might argue only certain type of clouds (depending on their agenda) are seeded by CR, I don't know much about CR to comment on that. All I can say is: in the present trend, they seem to try reinforcing the fading "it's the sun" myth by pointing out that sun's energy variation has a positive feedback from CR. It seems now, that the feedback, even if positive, looks miniscule, unable to explain the Earth energy budget and its history.

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  3. suckfish,

    You can access the AR5 chapter on clouds and aerosols here, Chapter 7, describing the complexities and uncertainties and giving best estimates.

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  4. suckfish @1 - it depends on the type of cloud.  As a general rule, low level clouds tend to have a net warming effect while high level clouds tend to have a cooling effect.  Cosmic ray theory suggests more low level clouds would form.

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  5. Sorry, I got that backwards @4!

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  6. Dana, thanks for an informative summary of recent work.  Although there doesn't seem to be any contribution from cosmic rays to the secular trend of temperature, there does appear to be a correlation between CR and decadal temperature fluctuations.  Of course, that correlation may just result from the correlation of CR with total solar irradiance (TSI).  You could add Foster and Rahmstorf (Environ. Res. Lett. 6 (2011) 044022) to the evidence against a strong CR influence on temperature.  They found that the amplitude of the TSI effect on temperature fluctuations since 1980 is no more than 0.05C.  The TSI effect would implicitly include any CR effect.  Since the sun is quieter now than it was in 1980, they found a small negative net solar effect from 1980 to 2011. 

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  7. dana@5,

    You've got it opposite to me@2, therefore one of us must be wrong.

    All of the credible resources, including our own graphic of Cloud Feedback point that you are wrong. The science of cloud feedback is not intuitive, so it's easy to get it wrong. Thhe best way to remember it is, as I pointed @2, by thinking of clouds as reflecting the sun in summer: low clouds (usually heavy and dark) "obstruct a lot of sun rays" therefore cool you down, especially in summer when the scorching sun may be unbearable. On the other hand, the high, very thin clouds (like jet contrails) have little influence on scorching summer sun. That's the main difference. Difference in IR absorbtion by low vs. high cloulds, although goes in the same direction of climate feedback, is not that signifficant.

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  8. chriskoz @7 - you're referring to me @4.  Me @5 points out that me @4 got low/high clouds warming/cooling backwards.

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  9. Few years ago I wrote about the beginning of the cosmic ray hypothesis from a different perspective.

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  10. Fall of 2009: Svensmark predicts an immediate and rapid cooling

    2010: Warmest year on record (tied with 2005)

    Svensmark has been much less outspoken in the last few years.

    Still heraleded as the man who proved AGW wrong by sections of the anti-science crowd, of course (and clueless MSM journalists, especially in Norway)


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  11. I'm disappointed that suckfish @1 got a down vote.  I see no reason to assume his questions were anything but an honest and relevant inquiry.  

    I do like the way chriskoz and Dana responded with a wealth of information; that's what makes this a great site.  That is, with the exception of chriskoz's admonishing opener, "Your assessment is simplistic and incorrect," a mischaracterization of suckfish's comment - suckfish was explicitly airing out an "impression," not making an "assessment," and even inviting the impression to be corrected.  All of us get wrong impressions from time to time due to gaps in our own level of understanding/expertise and/or incomplete information, and there's nothing wrong with that.  (What can be harmful is precisely when people mistake their own wrong "impressions" for thorough and sound "assessments.")  A purported "assessment" would reflect a belief by the speaker that she has considered enough of the relevant data and evaluating the conclusions of others to form her own firm conclusion.  It would not be accompanied by a question about what the latest research indicates, and it would not itself be punctuated by a question mark, both of which appear in comment #1.  

    I don't know if there may be some history related to any prior comments by suckfish in other threads that may have triggered the downvote and/or the (in my view, inaccurate, as explained above) admonishment, which might justify them in a private conversation, but in a public forum it would regardless tend toward giving a wrong impression to anyone unaware of that history that we here at SkS are quick to assume anyone questioning any part of the main post is just a troll to be criticized and condescended to.  

    I think I speak for the community of regular visitors and contributors (my own small contribution so far consisting entirely of a single Spanish translation of the "ocean acidification is not a problem" climate myth, though I aspire to pick up the pace soon and start adding more translations) when I say we want to encourage honest and relevant inquiry, and that there is no shame in approaching an issue with initial impressions that may turn out to be incorrect.  

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    Moderator Response:

    [PW} I agree: the never-ending onslaught of denier drivel has had, unfortunately, a corrosive effect on even the most genial of discussions and some--I am not absolved in this either--of us have an 'itchy rigger finger,' when we think we see a concern troll in its initial salvos.

    I think it instructive, this bit of behavior and the poster's observations about it, and urge all to give everyone who visits SkS the benefit of the doubt, unless/until they show what their true motives are in commenting here.

  12. Listen to what Richard Alley has to say about cosmic rays and global warning 42 minutes into this lecture from 2009. A better version of the graph in the video can be seen here.

    Why waste time and resources at the particle accelerators like the one at CERN when Nature did this experiment for us under far more realistic conditions about 40,000 years ago?

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  13. jdixon1980@11,

    Your critique and an explanation of "assessment" term (that I have not been understanding as deeply as you do) is duly noted and up-voted. Thanks.

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  14. HK@12

    It is necessary to test hypotheses in realistic experiments. So i do not think it is a waste of time what they have done at CERN. You must know that they did not only test Svensmarks hypothesis of cosmic rays seeding cloud condensation nuclei, but also other factors which may have influence on seeding clouds.

    There is a (in my onpinion) very important article in Nature 17.oct 2013 vol 502 Almeide et Al.

    Molecular understanding of sulphuric acid-amine particle nucleation in the atmosphere


    They find a natural presence of Dimethylamine dwarfing cosmic rays in their effect on cloud nucleation. This is a direct result from the CLOUD experiment at CERN.

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  15. Well, it only confirms what Richard Alley told us 4 years ago, doesn’t it?
    Since a huge increase in cosmic rays didn’t have a noticeable impact on climate 40,000 years ago the conclusion from CERN isn’t very surprising. Unless of course, the assumed link between cosmic rays and the beryllium-10 isotope is wrong.

    BTW, is Dimethylamine somehow related to Dimethyl sulphide? James Lovelock (the guy behind the Gaia hypothesis) has proposed that Dimethyl sulphide emitted from some marine algae play an important role in cloud formation over the oceans.

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  16. HK

    Dimetyl amine and dimethyl sulphide are two very different chemicals, but both involved in cloud condensation. The mechanism discussed in the nature paper from the CERN lab is, that dimethyl amine is stabilising clusters of sulphate ions in the atmosphere, enabling them to grow. exactly that, what Svensmark thought was an effect of cosmic rays.

    Dimetyl sulphide is mostly released by algae, dimetyl amine is released over land too and is related to huiman land use there.

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