Relationship of Lower Tropospheric Cloud Cover and Cosmic Rays

by Judith Curry

A new paper is in press that sheds some light on the relationship between cosmic rays and lower tropospheric cloud cover.

Relationship of Lower Troposphere Cloud Cover and Cosmic Rays: An Updated Perspective 

Ernest M. Agee, Kandace Kiefer and Emily Cornett


An updated assessment has been made of the proposed hypothesis that “galactic cosmic rays (GCRs) are positively correlated with lower troposphere global cloudiness.” A brief review of the many conflicting studies that attempt to prove or disprove this hypothesis is also presented. 

It has been determined in this assessment that the recent extended quiet period (QP) between solar cycles 23-24 has led to a record high level of GCRs, which in turn has been accompanied by a record low level of lower troposphere global cloudiness. This represents a possible observational disconnect, and the update presented here continues to support the need for further research on the GCR-Cloud hypothesis and its possible role in the science of climate change.

In press, Journal of Climate.  Abstract [here].

Ernie Agee has kindly made available a near final draft of the paper, which is posted here [Agee cosmic rays].

The Introduction starts with a good overview of the relation between solar activity and clouds, starting with the 1997 paper by Svensmark and Friis-Christensen.

From the Conclusions:

Several studies, as referenced here, have continued to promote the controversial cosmic ray-cloud connection hypothesis, both from the standpoint of errors in data analysis as well as scientific links that establish GCR-CCN as a viable contributor to climate change. It is also important to note (see Carslaw et al. 2002) that there are two mechanisms by which cosmic rays may affect cloud droplet number concentrations or ice particles: a) Ion-aerosol clear-air mechanism, and b) Ion-aerosol near-cloud mechanism. Recent attempts have also been made to further resolve the GCR-CCN controversy by examining the global cloudiness response to very short-term solar variations (namely Forbush Decreases that are approximately of one-week duration). Calogovic et al. (2010) have found no response in global cloud cover to Forbush Decreases at any altitude and latitude. Svensmark et al. (2009), however, have shown that Forbush decreases associated with CME passage results in lower troposphere clouds containing less liquid water. Their results, in general, show global scale influences of solar variability on both cloudiness and aerosols. The work by Harrison and Ambaum (2010) also shows a positive relationship between cloudiness and large GCR changes associated with Forbush decreases (as observed at Shetland, England). Laken and Kniveton (2011) on the other hand, fund no evidence of any relationship between liquid cloud fraction and GCRs.

It is concluded that the observational results presented, showing several years of disconnect between GCRs and lower troposphere global cloudiness, add additional concern to the cosmic ray-cloud connection hypothesis. In fact, this has been done in the most dramatic way with the measurement of record high levels of GCRs during the deep, extended quiet period of cycle 23-24, which is accompanied by record low levels of lower troposphere global cloudiness. Research on the GCR-cloud correlations must continue, particularly in view of the two physical mechanisms mentioned above (as well as the uncertainty in the reliability of the ISCCP lower troposphere cloudiness to show the proposed correlations). Finally, it is clearly known that other factors can affect mean global cloudiness besides solar variability, due to internal forcing mechanisms on different time scales (such as ENSO).

JC comment:  Trying to identify a GCR signal in  cloudiness is confounded by a plethora of other dynamical and thermodynamical processes that can modify cloud properties, notably the  teleconnection regimes such as ENSO and the internal decadal oscillations.  Both mechanistic research (such as the CERN experiment) and climatological analyses such as done in this paper are needed to support progress in understanding this issue.

Update:  RealClimate has a post regarding the CERN CLOUD experiment that provides a good overview, explaining the proposed physical mechanisms for cosmic rays to influence climate.

Moderation note:  This is a technical thread, and comments will be moderated for relevance.

95 responses to “Relationship of Lower Tropospheric Cloud Cover and Cosmic Rays

  1. How does this paper “shed some light” on the issue? There is no actual analysis other than a ‘by eye’ conclusion that the trends in Low CC don’t match CR changes. Something reported in Damon and Laut, more recently in Gray et al (Revs. Geophys). I have to say this is remarkably thin gruel for a J. Climate paper….

  2. Nigel Calder, coauthor with Svensmark of The Chilling Stars, has this post on the Forbush decreases. He has links which support the GCR – cloud connection.

  3. I cannot but help think that if they wanted to find a correlation they would have done the normal data transformation, inversion, split, splice, reposition, lag reduction and then invented a statistical method with would convert a r2 of 0.0001 into a rho of <0.01.
    Think I will await someone with a background in actual science to publish.

  4. The new paper shows a disconnect between GCRs and tropospheric low cloud cover. One thing seemingly omitted from this paper is an analysis of diurnal temperature range (DTR) (cf GCR) which Svensmark correlates with Forbush Decreases.
    The recently published results from the CLOUD experiment (Kirkby et al) seem
    to be understated compared to

    • Since DTR is only a proxy for cloudiness it would hardly add anything to the conclusion. If you can measure cloudiness directly rather than inferring changes in cloudiness from a change in DTR you are on better footing.

      • I was also thinking about the relationship between DTR and cloud cover – after all there has been much ado about temperature and I understand there can be problems with satellite estimates of low cloud due to clouds at intermediate and high altitudes. (Incidentally, how is nocturnal cloud extent measured?) Proof of the pudding so to speak.
        Please forgive a non-‘climate scientist’ for intruding on the turf.

  5. Judy – I agree that the RC piece you linked to provides a good overview.

    I have never had trouble accepting the GCR/cloud hypothesis. It’s plausible, and even before the recent CERN data, Svensmark had provided experimental evidence in its favor. The problem has always involved quantitation. Many factors affect clouds, including aerosols as just one set of factors, and the effect of aerosols itself can also represent many different mechanisms. As the RC post and many previous analyses have shown, among all cloud modifying influences, the effect of GCR variations is likely to be extremely small, and easily masked by other influences operating in a different direction. This conclusion can be inferred from the physical chemical behavior of the relevant species of ions and atmospheric chemical constituents, and so correlational analyses serve as an independent source of confirmation.

    We have not heard the final word on this topic, and the research should proceed, but at this point, I see the burden of proof as falling on those who would like to suggest that the GCR effect is non-trivial.

    • Fred Moolten

      We have not heard the final word on this topic, and the research should proceed, but at this point, I see the burden of proof as falling on those who would like to suggest that the GCR effect is non-trivial.

      Yes. Let’s see what the CLOUD experiment at CERN shows us.

      And, yes, the “burden of proof” is always on those who would like to suggest a hypothesis (a point, which appears to have eluded Kevin Trenberth in his apparent attempt to reverse the “null hypothesis” – see earlier thread).


      • The burden of proof falls on those who would like to suggest that the CO2 effect is non-trivial. Thanks, Fred.

  6. Another interesting cosmic ray research group:
    Galactic Cosmic Rays – Clouds Effect and Bifurcation Model of the Earth Global Climate. Part 1. Theory, Vitaliy D. Rusov et al. Journal of Atmospheric and Solar-Terrestrial Physics Vol. 72 (2010) p. 398-408

    Galactic cosmic rays—clouds effect and bifurcation model of the Earth global climate. Part 2. Comparison of theory with experiment Vitaliy D. Rusov et al. Journal of Atmospheric and Solar-Terrestrial Physics Volume 72, Issues 5-6, April 2010, Pages 389-397

    • “It is obvious that by virtue of Eq. (18) the decrease in angular velocity of the Earth liquid core
      leads to the increase not only of angular velocity of the Earth solid core but also of the mantle rotation
      velocity. This means that the sharp change of mantle rotation velocity will cause strong friction
      between the lithosphere and surface layer of the atmosphere that, in its turn, will lead to the sharp
      increase in average temperature of the Earth surface and troposphere. “

      • Add this to some research I read mentioned elsewhere about the Earth supposedly expanding slowly (decreasing in density) by ~4mm/y^-1. But none of this seems like it could work on time scales that we’re seeing, but only over thousands or tens of thousands of years for noticeable impact. And if the mantle is changing rotational speed fast enough to impact crust-atmosphere friction, shouldn’t we see other effects in earthquakes and volcanoes?

        The ideas in this article about GCR increasing and lower troposphere clouds decreasing is also very curious, and also doesn’t seem to link with the observed temperature record from what I can see.

        So many random leads… it feels like this is all turning into spaghetti research. We need some comprehensive quantization to start getting this all cleared up…

  7. Judith, how difficult is it to artificially generate GCR’s from a research airplane? Perhaps NOAA could conduct an experiment by flying through clear sky and measure the effect of GCR’s on tropospheric low cloud cover. It is time to bring some closure to this important issue.

  8. Jeffrey Pierce at RC

    If CCN are exposed to relative humidities above 100%, cloud droplets will form on them.

    Cloud Condensation Nuclei (CCN)

    Is it possible for relative humidity to be greater than 100%?

  9. The paper seems worthy enough to me, they do show that the previous relationship between GCR and low cloud cover (which was pretty weak, but you can eyeball it on the graph) has broken down. During very high GCR density in recent years, cloud cover (at least on this measure) has fallen quite sharply.

  10. I was recently musing on this relationship and began to notice there are several other disconnects occurring at a similar time with a similar trend.

    I’ve put them here on my blog:

    My speculative conclusion was that the common theme is that temperature is deviating from other (disparate) measurements which ought to correlate.I’ve got a hunch that some other driver is out there – the disconnect is so widespread that I though maybe pollution in some way.

    Unfortunately, since 1980 we enter the world of “fairytale” measurements which cannot be relied on.

    • Scottish Sceptic, I assume the quoted reference to “Shetland, England” actually refers to the Shetland Islands off the north coast of Scotland? Or is there an English location of that name?

    • interesting analysis

    • Well, now I am sure of it! I have contracted cyclo-mainia. At least I tend to see the odd temperature relationship change between the mid trop and strat around the 1994 period.

    • The same happens with SCL/temperature correlation. Allegedly it gets weaker after ~1980. Tree rings too.

    • ” since 1980 we enter the world of “fairytale” measurements which cannot be relied on.”

      What, as opposed to before 1980, when measurements were magically more reliable?

      I’ll wait for BEST, and check out what they argue in their reports about temperature, before I lament the poor efforts we make in general to measure key indicators globally. So I know how sorry a state we are in better.

      • Watch Courtillot above for clues.

      • er, below.

      • kim

        What is this preoccupation with the Wild Things in the pants under the bed?

        I mean, I don’t put a lot of credence in psychology, however one wonders..

      • kim

        Courtillot is kinda skeery, despite his veneer of refinement.

        One must be extremely careful listening to and interpreting what the fellow says, as his meticulously selected phraseology is full of pitfalls.

        For instance, early on in his presentation, Courtillot makes the quite bland assertion that there is NO SUCH THING AS GLOBAL CLIMATE.

        In so doing, he does not seek to replace ‘global climate’ with ‘ensemble of regional climates’ or any like term or concept. Courtillot simply and without ceremony kills off even the concept of discussing global effects on global scale.

        How then could one do anything but conclude no global effect, per Courtillot’s reasoning, given the unnecessary assumption of no global effects?

        Courtillot’s circumlocutions amount to an elaborate charade of diverting the audience’s attention long enough to forget what he’s done here.

        Dismiss the valid and obvious global scale data to contemplate the higher noise:signal regional graphs?

        When he must well know that the two cherry-picked datasets he places before us are dominated by regional natural signals within the timescale he has chosen?

        His cynicism and duplicity ought raise alarm bells with any skeptical mind.

      • Yes, I can see why Courtillot scares the pants off of you. Courage like that isn’t expected.

      • Speaking of BEST, weren’t they supposed to come out with results awhile ago? I’d love to hear an update on what’s going on with them.

      • Coming soon!

  11. JC comment: Trying to identify a GCR signal in cloudiness is confounded by a plethora of other dynamical and thermodynamical processes that can modify cloud properties, notably the teleconnection regimes such as ENSO and the internal decadal oscillations.

    Firstly the troublesome properties of the cloud response mechanism to energetic particles is a distraction from the underlying physics in externalities generated by said causal processes.

    These are a legitimate line of enquiry,with an inverse relationship to troublesome properties in the solar cycles ie the amplitude,spectral irriadiance and changes in the upper and middle atmosphere chemistry and dynamics (read transport.) eg Baumgaertner et al 2010A

    The Earth’s middle and upper atmosphere are strongly influenced
    by solar variability. Changes in the solar spectral irradiance as well as in the solar wind can lead to significant perturbations. Solar wind disturbances have been shown to lead to geomagnetic activity variations, which can result in magnetospheric loss of electrons (e.g. Clilverd et al., 2006). These electrons precipitate into the atmosphere at high geomagnetic latitudes where they lead to the production of NOx,
    termed energetic electron precipitation (EEP) NOx, through dissociation and ionisation processes. Downward transport in the dark polar winter can lead to significant enhancements of NOx in the stratosphere. Because NOx can catalytically destroy ozone, such NOx enhancements lead to ozone depletion in the upper stratosphere as has been shown e.g. by Callis et al. (1998), Brasseur and Solomon (2005), Jackman et al.
    (2008), or Baumgaertner et al. (2009). In the mesosphere, the mean meridional circulation transports air from the summer to the winter hemisphere driven by gravity wave energy and momentum deposition as well as radiative heating and cooling (Brasseur and Solomon, 2005). In the polar winter, this circulation can transport air, including EEP induced NOx enhancements, from the mesosphere into the stratosphere. In the polar stratosphere, further downward transport is controlled by the Brewer-Dobson circulation (BDC). The BDC is responsible for the meridional transport of air in the stratosphere:It mainly consists of poleward transport in the middle and upper stratosphere, with rising air in the tropics and downwelling air in the polar regions.

    Baumgaertner et al 2010B is an interesting paper similar to callis 2001 Rozanov 2005 Seppala 2007

  12. It should be remembered that the Earth’s magnetic field is by far the strongest modulator of the incoming cosmic rays. Geomagnetic field is not static it is in a continuous ‘flux’, most notable changes are in the Northern Hemisphere, where the gmf responds to the solar activity.
    In the North West quarter-sphere dominated by the Hudson Bay pole this is a negative correlation. In the North East quarter-sphere dominated by the Siberian pole correlation is positive. These changes and correlation on the decadal and most recently the daily changes (graph 5) are graphically shown here:
    where you can see the immediate impact of each recent geomagnetic storm.
    Climate change is related to the activity but not via quantitatively insignificant cosmic ray count, but via far stronger geomagnetic changes and atmosphere (from tropo- to stratosphere) ionisation.

    • Thank you for this. As a non ‘climate scientist’ I am trying to understand the complexities of climate science but cannot claim to fully comprehend these data. I have a couple of questions.

      Is it the case that for most of the time Earth’s GMF (as opposed to direct solar magnetic field and solar wind influences) dominates the CRF except when a solar coronal mass ejection heads our way the Earth GMF is overwhelmed producing a Forbush decrease? If so how does that correlate with diurnal temperature range (at times other than following FDs)?

      I read somewhere that solar magnetic field influences the Earth GMF.
      Is this combination together with CRF and the ion-aerosol near-cloud hypothesis a possible/partial explanation for climate change?

      Most of the debate around CRF seems to discuss clouds to the exclusion of much else. What of the combination of (aerosols + clouds) which must be of relevance in the real world?

      • UV on phytoplankton, too.

      • Sorry to disappoint, but I would not be able to answer your questions with required degree of competence.
        My aim is to make people aware of the alternative factors as contained in the data available from ’reliable’ sources.

      • Nobody’s got competence in this one.

      • UV on phytoplankton is interesting. Micro-organism concentration on all the wavelengths from UV to green is more entertaining. If I remember correctly, roughly 10% of incoming solar is absorbed below 10 meters. The concentration of micro-organism varies the depth of absorption changing the mixing layer average depth. I got know clue how to quantify the effect.

      • Look at the chemicals released.

      • To expand, A climate response to the small changes in solar is like to be a low frequency response. A small change in deep ocean heat uptake seems to make sense because the heat transfer rate is slow enough for it to have a cumulative effect. Atmospheric cooling is a lot slower than warming. The sulfates may have a long enough duration, but it seems unlikely.

      • Some elements of the radiant phenomena from the sun have large changes, UV among them.

      • I agree completely. The sulfates would enhance the impact. I just believe the decrease in optical depth and incident wave lengths in general is what should be the focus.

      • The shape of cosmic ray peaks alternate from flat to sharp in alternate solar cycles. Approximately three solar cycles fit in one phase of the PDO, which means the phases alternate between two flat peaks and two sharp peaks. This is a clockwork mechanism to explain some of the data.

        Leif calls those cosmic ray peak shapes a second order effect, but we’re well into second order effects here. I have no data to back up this speculation, numbers limited to fingers and toes, but there is explanatory power. This clock can still be perturbed by Koutsoyiannis, and function.

      • Couple of second order effects synchronized can be a first order PITA. :)
        Leif puts more stock in the PDO shift than the solar minimum. Normally that would definitely be the case. With apparent prolonged minimum, synchronized with a cool PDO plus a cool AMO, there is something to consider. GCR/clouds may provide a boost, dunno. The internal cycles are a little out of sequence, but there should be 9.5 and 15.3 year quasi-cycles. How those make link up with the solar cycles I will let the cyclomaniacs deal with. To me, solar absorption below ten meters, whatever the cause, is something to watch, especially in the southern oceans.

      • I can’t disagree. Thanks, you’ve helped me here.

      • My clock can take a lickin’ and keep on tickin’, cuz the lickin’s here on earth and the tickin’s in the sun.

      • look at the lifetime of the chemicals released.

      • What do they do while alive?

    • The thing people call “cosmic rays” is actually neutron count rate. Consider the possibility of misinterpretation.

  13. Christopher Korvin

    About 30 years ago I visited the (excellent) San Diego Science museum.One exhibit was a cloud chamber of I think alcohol vapour.As the various cosmic particles winged there way in from outer space they travelled through the vapour and left trails resemblimg the con trails of aircraft.Each type of paricle left a characterstic pattern of con trail.This apparently enabled the scientists to dermine which particles they were.Also,entertainingly,though not scientific the exhibit linked a tone,pinging,or warbling,or whining , to each type of particle. Very thrilling to watch and to consider these particles were travelling through my body just as easily as throught the cloud chamber,no doubt damaging my DNA on the way through. So I dont know whether these particle alter the earths climate by creating clouds but I do know they are capble of creating clouds in a cloud chamber.I know this because I have seen it myself.

  14. The paper featured in this article is NOT based on sound conception. It doesn’t even reference the landmark paper that towers above all others on solar-terrestrial relations:

    Le Mouël, J.-L.; Blanter, E.; Shnirman, M.; & Courtillot, V. (2010). Solar forcing of the semi-annual variation of length-of-day. Geophysical Research Letters 37, L15307. doi:10.1029/2010GL043185.

  15. If we assume people like Rhodes Fairbridge are correct and there is a link between solar magnetic effects and world climate, it seems to me that this link must be quite complex. From the Maunder minimum, sunspots started to disappear around 1645. However, the coldest winters in the UK occurred some 40 years later, around 1685. If Livingston and Penn are correct, this time around sunspots may start to disappear around 2017 or 2020. If there is another 40 years before we get the coldest temperatures, these will not occur before 2060 or so. However, I have seen no explanation for this sort of timing.

    • The Maunder spots were sparse, large and primarily southern hemispheric. I think that somehow the butterfly wing of tidal effects van de Graf to the surface.

      • Lief doesn’t, needless to say.

      • er, Leif.

      • I tend to agree with Leif. It would have to be a synchronization of several minor impacts. Unfortunately, the same relative cycles of the solar patterns are common with many chaotic (quasi-chaotic) systems, so it is hard figure out what is solar versus what is internal.

      • I was just talking about the sun. I’d still have to get from sunspots to the earth, and your point holds.

      • The verb ‘van de graf’ to the surface (of the sun) confused you. It’s a metaphor, because I’m confused, well, ignorant anyway.

      • I think the Maunder spots are a huge clue. Why were they different?

      • “I think the Maunder spots are a huge clue. Why were they different?” They are a huge clue. As for why they were different? When you have more turbulent mixing spot would tend to generally smaller and more dispersed. Less turbulent mixing, fewer and potentially larger spots. like a lava lamp. Same thing with air. Move water vapor and less turbulent mixing changes the rate of heat flow. Lots of neat things can happen.

        For example, increased specific humidity means the air weighs more. Moist air is still going to rise, but the mass of dryer air descending would be greater. There would be an increase in sensible heat transfer. as well as increase radiative cooling. More moisture increases the percentage of mid atmosphere initiated convection. With less turbulent mixing, there would be larger blobs, like a lava lamp.

        See, the sixties were not a complete waste :)

      • Well, if it’s less turbulent mixing, which I doubt because the dynamics are still there, just less visible, then does less mixing lead to a cooler earth.

        My question depends upon the spots modulating earth’s temperature. Isotope data is ambivalent and it did cool during the Maunder Minimum.

      • Or, of course, the same process modulating both spots and the earth’s temperature.

      • “My question depends upon the spots modulating earth’s temperature. Isotope data is ambivalent and it did cool during the Maunder Minimum.” I would say that it is highly likely that conditions that lead to the sun spot changes in the Maunder lead to decreased temperatures on Earth. The mechanisms involved are not easy to see because of the differences in the internal cycles of Earth’s climate. A simple way to look at the possible mechanism is a pebble dropped in a still pond has a more noticeable impact that one dropped in a fast moving stream. Drop two pebbles at a distance apart at the same time and some of the ripples and larger and smaller. So it would be difficult to see the mechanism in more chaotic environments. If this minimum is prolonged, we will probably see the ripples.

      • Oh, a lovely image.

      • Chaos in both pebbles and a tenuous link. Yeah, it’ll be a while.

      • Reminds me of the song “Blue on Black.” If magnetic effects modulate clouds, most of the Sun’s energy impacts the oceans, which are known to have long cycles and a large heat capacitance. Couldn’t the oceans account for the 40 year lag?

      • “Reminds me of the song “Blue on Black.” If magnetic effects modulate clouds, most of the Sun’s energy impacts the oceans, which are known to have long cycles and a large heat capacitance. Couldn’t the oceans account for the 40 year lag?” If it were only so simple. Most of the ocean heat action is in the mixing layer and the mixing layer depth doesn’t have to be constant, not does the percentage of solar energy absorbed in the mixing layer need to be. Brings me right back to the lava lamp.

        What is interesting about the solar energy changes with cycles is that UV has a larger decrease and near IR has an increased. Both are small but impact different regions of the atmosphere and oceans.

      • Yah, there’s a metronome. Tick tock, tick tock, tickety tock.

  16. Norm Kalmanovitch

    This is rather complex stuff and it will be years be the scientific investigation into this process converges on a clear understanding of the precise effect of cosmic rays on cloud formation and the even more complex effect that clouds have on global temperature.
    On the other hand we have near perfect understanding of the interaction between increased atmospheric CO2 and its effect on the Earth’s OLR (mistakenly referred to as the greenhouse effect).
    We can use MODTRAN models to demonstrate the difference in effect from the 100ppmv increase in atmospheric CO2 that occurred between preindustrial times when the level was 280ppmv level to the recent 380ppmv level and what that effect would be for a doubling to 760ppmv and a quadrupling to 1520ppmv.
    It is clear from physical measurements dating back to the 1970 Nimbus 4 data that the effect claimed by all of Hansen’s models presented in the SCIENCE 28 August 1981Hansen et al paper “Climate Impact of Increasing Atmospheric Carbon Dioxide” in which Hansen claims “The most sophisticated models suggest a mean warming of 2° to 3.5°C for doubling of the CO2 concentration from 300 to 600 ppm” is between five and eight times greater than what the physical measuements and MODTRAN models demonstrate to be physically possible.
    (SCIENCE, VOL. 213, 28 AUGUST 1981)
    The more recent paper by Hansen et al that started this climate change issue depicts an even greater value of 4.2°C for a doubling from 315ppmv to 630 ppmv, Hansen also discusses a low sensitivity range between 1.5°C and 2°C and a high sensitivity range between 4°C and °C for a doubling of CO2, both of which are well outside what is physically possible according to measurements and corroberated by MODTRAN models.
    Whatever weaknesses there are in the cosmic ray cloud theory unlike the Greenhouse gas theory which is contradicted by all physical data and by all rights should have long since been discarded as a viable hypothesis; the cosmic ray theory is still perfectly valid with no contrary evidence to this hypothesis found to date.
    In other words AGW is no longer scientifically valid but the hypothesis linking cosmic rays to cloud formation as an amplification of solar changes affecting global temperature still is scientifically valid.

  17. Dr. Spencer informs us that tropospheric convection would not exist without the effect of greenhouses gases and that without a “greenhouse effect… the atmosphere would become isothermal, and thus very convectively stable.” That is a given

    Linked to what happens in the troposphere are galactic cosmic rays and solar activity. According to Nir J. Shaviv, changing solar activity is responsible for varying solar wind strength. A stronger wind will reduce the flux of cosmic ray reaching Earth, since a larger amount of energy is lost as they propagate up the solar wind. The cosmic rays themselves come from outside the solar system. Since cosmic rays dominate the troposphere ionization, an increased solar activity will translate into a reduced ionization.”

    Additionally, as Shaviv points out, reduced ionization also results in “a reduced low altitude cloud cover. Since low altitude clouds have a net cooling effect (their ‘whiteness’ is more important than their ‘blanket’ effect), increased solar activity implies a warmer climate.”

    Accordingly we must look to changes in solar activity, not to mention variations in galactic radiation itself—wholly unrelated to the solar activity—as the Earth dashes through the spiraling arms of the Milky Way.

    Nominally, however, it’s the sun, stupid. Idso and Singer in “Climate Change Reconsidered” note what others have shown that, “small changes in solar output can indeed induce significant changes in earth’s climate.”

    For example, research “suggests that small changes in solar output may influence Atlantic variability on centennial time scales.” ~Black et al. (1999)

    And, “the climate system is far more sensitive to small variations in solar activity than generally believed… “It could mean that the global temperature fluctuations during the last decades are partly, or completely explained by small changes in solar radiation.” ~Van Geel et al. (1999)

    Idso and Spencer point to Feynman and Remaking (1999) on the subject of climate in the twentieth century as they relate to “changes in the intensity of cosmic rays incident upon the earth’s magnetopause and their transmission through the magnetosphere to the upper troposphere.” According to Feynman and Remaking, “the intensity of cosmic rays incident on the magnetopause has decreased markedly during this century… [And] the pattern of cosmic ray precipitation through the magnetosphere to the upper troposphere has also changed.”

    For example, Feynman and Remaking noted that “at 300 Me the difference between the proton flux incident on the magnetosphere at the beginning of the century and that incident now is estimated to be a factor of 5 decrease between solar minima at the beginning of the century and recent solar minima,” and that “at 1 Gee the change is a factor of 2.5.”

    Commenting on the above findings, Disso and Spencer recap the findings of the these phenomena, noting that, “the part of the troposphere open to cosmic rays of all energies increased by a little over 25 percent and shifted equator ward by about 6.5° of latitude. And with the great decrease in the intensity of cosmic rays incident on earth’s magnetosphere over the twentieth century, one would have expected to see a progressive decrease in the presence of low-level clouds and, therefore, an increase in global air temperature, as has indeed been observed.”

  18. As an interesting aside, we have two very large old buildings here in Orange County CA. Each one housed about eight huge blimps during World War II. Each blimp had a footprint of about an acre. These blimp hangers are very tall and the doors are very tall. On more than one occasion I have heard people (including old timers who worked there during World War II) say the buildings were large enough to form their own weather systems. Some days it would rain inside the building while not raining outside. Not that this question means anything to the cloud debate, but I was wondering: Do GCRs have the ability to pass through a solid structure like a roof built to withstand an aerial attack?

  19. As we have the 14C record of tree rings and also have tree ring widths; is there any correlation between 14C anomalies, normalized for radioactive decay, and ring width anomalies?

  20. Climate4You page on climate & clouds shows:
    Low level clouds have been decreasing while mid level clouds have been increasing.

    Note that the low and mid level clouds are out of phase with each other.

    Are the cosmic rays impacting the mid level clouds and not the low level clouds?

    There was a recent paper indicating that the solar UV and IR trends were opposite during the solar cycle.
    The solar UV was exceptionally low this last solar minimum. See

    Was UV spectral solar irradiance lower during the recent low sunspot minimum? Mike Lockwood, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 116, D16103, 11 PP., 2011 doi:10.1029/2010JD014746

    Another trend to consider is the rapid increase in coal use in China. See graph of global coal This may have a corresponding increase in coal power related aerosols etc.
    How do “clouds” correlate with “aerosols” vs with galactic cosmic rays?

  21. My approach to most climate issues — since I can’t get into the depths of models — has been empirical: is nature is acting the way models say it should?

    At least 5 years ago there were papers showing that low level cloudiness didn’t increase when cosmic rays were higher (in the context of what are normally 11 year solar cycles). For now, it doesn’t seem to me that the cosmic ray theory is holding up, but as always, new research may change my mind.

    Yet it is true that in this quiet phase of the sun, surface temperatures haven’t increased, and sea levels haven’t risen.

    If a quiet sun is a cause of the lack of warming and lack of sea surface rise, then is there another possible mechanism?

    Yes, that of Johanna Haigh, who proposes that when the sun is more active, although the increase in total irradiance is on the order of 0.1% increase, UV can increase by as much as 7%. This would create more stratospheric ozone, which is a GHG. Her theory suggests that this warming in the stratosphere would move polar jets higher, toward the poles, bringing greater warmth to high temperate areas.

    The opposite would be true as well: when the sun is quiet, then there would be less UV, and the polar jets would move toward the equator.

    I hope I’ve summarized Haigh’s theory accurately. If the cosmic ray theory is wrong, but if the sun’s activity still has more influence on earth’s climate that the tiny changes in total irradiance would suggest — in other words, if the near lack of sunspots for 70 years in the Maunder minimum was causally related to the Little Ice Age — perhaps Haigh’s theory can be reexamined?

    • Haigh’s theory is interesting, with a prolonged solar minimum you have not only less UV but also nearly the same near IR, possibly an increase. A higher percentage on the near UV would be absorbed by water vapor in the upper troposphere creating a small shift in the radiative balance. That could enhance her theory. I am still not sold on the GCR/cloud impact, though it may help enhance cloud stability.

  22. The idea of GCRs affecting cloudiness and thence climate has been around since forever (Eli once found a reference to this in a 1950s paper), and folk have been looking for it forever. The obvious conclusion is that any effect is small.

  23. Dr Curry – there is a recent release on this topic.

    “Based on the results of decadal correlation studies between International Satellite Cloud Climatology Project detected cloud anomalies and the galactic cosmic ray (GCR) flux it has been suggested that a relationship exists between solar activity and cloud cover. If valid, such a relationship could have important implications for our understanding of recent climate change. In this work, we present an analysis of the first decade of MODerate Resolution Imaging Spectroradiometer (MODIS) detected cloud anomalies, and compare the data at global and local geographical resolutions to Total Solar Irradiance (TSI), GCR variations and the Multivariate El Niño Southern Oscillation Index. We identify no statistically significant correlations between cloud anomalies and TSI/GCR variations, and conclude that solar related variability is not a primary driver of monthly to annual MODIS cloud variability. We observe a net increase in cloud detected by MODIS over the past decade of ~0.58 %, arising from a combination of a reduction in high – middle level cloud (−0.31 %) and an increase in low level cloud (of 0.89%); these long term changes may be largely attributed to ENSO induced cloud variability.