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  1. Thanks for a very useful summary. Hadn’t even heard of the ‘near-cloud’ hypothesis!

    Comment by Kevin McKinney — 26 Sep 2011 @ 7:40 AM

  2. Dr. Pierce, Very nice article! I thoroughly enjoyed it.

    Comment by TL — 26 Sep 2011 @ 7:45 AM

  3. Dr. Pierce,
    You mentioned (briefly) solar energetic particles as distinct from cosmic rays; while there is a different origin, the primary particle energies can be comparable. However, the largest solar events can cause an increase in neutron monitor counts, known as a ground level enhancement or GLE. Mironova et al 2011 looked at the largest recent GLE (20 Jan 2005), finding considerable atmospheric ionization. What they did not find was anything else out of the ordinary, concluding “the observed atmospheric effect for this extreme GLE event was barely significant. No clear atmospheric effect was found beyond statistical fluctuations for the weaker SEP event of 17 January 2005, which is a typical SEP event. This implies that only extremely hard-spectrum (high energy) GLE/SEP events can produce a noticeable direct effect on aerosols in the polar low-middle stratosphere.”

    Perhaps this is verification that the mechanism shown in your Figure 4 works.

    Comment by muoncounter — 26 Sep 2011 @ 9:17 AM

  4. Thanks from me too. Could someone setup Figure 5 with a link to the fullsize image? The scaled version that appears on the page is difficult to read.

    Comment by Paul S — 26 Sep 2011 @ 9:24 AM

  5. Paul S: Here is the link for the full-sized figure 5 ( Can one of the RC folk link this?

    [Response: Done. – gavin]

    Comment by Jeff Pierce — 26 Sep 2011 @ 10:11 AM

  6. Thanks for this essay! This is a real contribution to the understanding of climate-related science among those trying to understand.
    Here is a link to [4] Svensmark & Friis-Christensen (1997):

    How do you get from 6% to 2% in this sentence? (btw how high or low are “low clouds”?)

    The reported observed relative change in low cloud cover [4] is ~6% with the solar cycle (or 2% absolute change in the fraction that low clouds cover the planet).

    What do you think of the point the AGW Observer makes here that the change in cloud cover found in [4] may be an artifact?

    Comment by Pete Dunkelberg — 26 Sep 2011 @ 10:14 AM

  7. Excellent explanation. What is clear is that SOx concentrations are limiting, but there may be synergistic effects from other species such as NOx. An interesting situation may occur when SOx is NOT limiting, such as over Mexico City as studied by the Molinas.

    Comment by Eli Rabett — 26 Sep 2011 @ 10:24 AM

  8. muoncounter: Interesting question. SEP events can have a strong affect on stratospheric chemistry with large changes in ozone and NOx concentrations (e.g. There is a long history of research on this; however, I don’t know if there is any connection between these stratospheric changes and changes in cloud cover, though this would be an interesting topic to explore.

    The Mironova paper shows very interesting results. However, something else must be going on in the stratosphere other than the clear-sky mechanism. Have a look at Figure 4 in Miranova. The aerosol extinction coefficients increase by an order of magnitude after the event. This could not be done without additional aerosol mass after the SEP because stratospheric aerosols generally have sizes that are near the peak in extinction efficiency. In other words, you couldn’t get an increase in aerosol extinction coefficient by an order of magnitude by changing aerosol size alone (if the clear-sky mechanism was acting alone, this would be the case).

    Thus something is clearly happening in the Mironova paper that is increasing aerosol mass. This might be a polar stratospheric cloud or perhaps a change in chemistry. I’m not sure exactly what it is, but it can’t be the clear-sky mechanism acting alone.

    Comment by Jeff Pierce — 26 Sep 2011 @ 10:27 AM

  9. Pete, in the ISCCP results low clouds cover ~30% of the Earth. The 2% change is the change in this value (e.g. 29% to 31%). Thus, the relative change in low cloud cover is around 6% (2/30*100).

    From the ISCCP data description page ( “low clouds have top pressures greater than or equal to 680 mb”. 680 mb would generally be 3-4 km above sea-level.

    I’ll take a look at your link to AGW observer tonight. Thanks!

    Comment by Jeff Pierce — 26 Sep 2011 @ 10:37 AM

  10. Dr. Pierce,

    Thank you for this interesting summary.

    I am interested in your thoughts on the work of Nir Shaviv, whom you haven’t mentioned.

    Dr. Shaviv wrote at his blog:
    …it is well known that solar variability has a large effect on climate. In fact, the effect can be quantified and shown to be 6 to 7 times larger than one could naively expect from just changes in the total solar irradiance. This was shown by using the oceans as a huge calorimeter (e.g., as described here). Namely, an amplification mechanism must be operating.

    He refers to Nir J. Shaviv (2008); Using the oceans as a calorimeter to quantify the solar radiative forcing, J. Geophys. Res., 113, A11101, doi:10.1029/2007JA012989.

    Best wishes
    Alex Harvey

    Comment by Alex Harvey — 26 Sep 2011 @ 10:46 AM

  11. Eli: Thanks for these thoughts. Nitrate, the aerosol species that comes from NOx tends to condense onto larger aerosols and do not aid in the growth of nucleated particles to CCN sizes. Organic aerosols, however, can dominate the growth of nucleated particles in many regions of the world. Organic aerosols and the affect of CCN are a very active area of research. Our work looking at the global sensitivity of CCN to cosmic rays does include organic aerosols (as well as a 2nd simulation where we increase the amount of condensible organics to test the sensitivity), The additional condensible material didn’t actually increase the sensitivity of CCN to cosmic rays. This is because the increase growth rates were roughly canceled by increase coagulation rates (do to more massive aerosols to scavenge the freshly nucleated particles). Still definitely an uncertainty though. Cheers.

    Comment by Jeff Pierce — 26 Sep 2011 @ 11:00 AM

  12. Very nice and clear — special thanks for the helpful graphics! The hurdles facing the “clear-sky” hypothesis will be known to anyone who’s followed this blog with an interest in solar connections, but though I’ve been vaguely aware of the “near-cloud” hypothesis (from brief mentions in AR4 and Gray 2010, I think), I haven’t seen it explained for us general readers before.

    Comment by CM — 26 Sep 2011 @ 11:37 AM

  13. Dr. Pierce,

    Thank you. An excellent post, both well organized and clear, touching on detailed science without being overwhelming. A good way to kick-start the brain on a Monday.

    Comment by Sphaerica (Bob) — 26 Sep 2011 @ 11:53 AM

  14. Alex Harvey: I know Nir Shaviv a bit (we were both external examiners on one of Svensmark’s students PhD defenses, and I got to chat with him a bunch then). As far as I know, his work mostly deals with the space physics end of cosmic rays and has looked at some historic climate correlations with cosmic rays. I don’t think he hasn’t worked on the aerosol/cloud physics side of things, so I am not extremely familiar with his work.

    The critical statement in Nir’s post is, “Since many regions of earth are devoid of natural sources for CCNs (e.g., dust), the CCNs have to grow from the smaller CNs, hence, the CCN density will naturally be affected by the ionization, and therefore, the cosmic ray flux.” Yes, CCN will change due to changes in ionization, but by how much? Even in regions without primary emissions (which can be anthropogenic as well as natural, e.g. combustion sources) changes in fractional changes in CCN will be smaller than fractional changes in nucleation/ionization due to slower growth and faster coagulation when nucleation is faster (e.g. Figure 4).

    Comment by Jeff Pierce — 26 Sep 2011 @ 11:58 AM

  15. Aren’t there dried salt specks over the oceans, black carbon and other dust in the Arctic, dust from Africa readily reaches Florida, bacteria are in the air most places. Where are the dustless places? Antarctica?

    Comment by Pete Dunkelberg — 26 Sep 2011 @ 12:54 PM

  16. Because of the thermal inertia of the oceans,the lack of any UHI effect and the fact that land temperatures do not reflect the changes in the enthalpy of the system the best indicator of global temperature trends is the Hadley SST data . The 5 year moving average shows the warming trend peaked in 2003 and a simple regression analysis shows a global cooling trend since then . The data shows warming from 1900- 1940 ,cooling from 1940 – about 1975 and warming from 1975 – 2003. CO2 levels rose steadily during this entire period. There has been no net warming since 1997 – 14 years with CO2 up 7% and no net warming. ( Check the actual data at the Hadley center)
    The Graph of the Cosmic ray flux linked in the post shows decreasing minima ( at solar max)through solar cycles 20 – 22 and integrating the total flux through that period and allowing for about a ten year time lag would correlate reasonably well with the temperature rise from 75 – 2003. Since the 22 flux minimum the cosmic ray flux increased to a peak not seen on rest of the graph in the 23 – 24 solar minimum . This matches rather suggestively the declining temperature trend since about 2003 and suggests that by 2020 temperatures will decline significantly.
    I think these empirical observations are more than co-incidence. I agree the mechanisms are still obscure.

    [Response: You are free to think what you like about coincidence, but the reality is that no one seriously things there should be a one-to-one correlation between the forcing (CO2 and other greenhouses gases) and temperature. This is a red herring, and the idea that one can use such short term correlations to predict what will happen in after 2020 is just plain silly. –eric]

    Comment by Norman Page — 26 Sep 2011 @ 1:20 PM

  17. Norman Page wrote: “There has been no net warming since 1997 …declining temperature trend since about 2003”

    Bore hole.

    Comment by SecularAnimist — 26 Sep 2011 @ 1:48 PM

  18. re Alex Harvey — 26 Sep 2011 @ 10:46 AM

    Shaviv’s paper doesn’t have anything necessarily to say about the cosmic ray flux Alex, and there are some problems with taking his interpretation at face value. Although one would like to make a direct comparison of ocean heat content (OHC) variation with respect to the solar cycle, Shaviv points out that these don’t correlate very well, and analysis of tide guage sea level variability forms a significant part of his analysis:

    “Given the relatively small correlation coefficient and modest significance, it is worthwhile to corroborate the existence of the large heat flux variations using an independent data set. We thus turn to analyze tide gauge data measuring sea-level variations.” and “Note that the relatively low correlation coefficient between the OHC and solar signals may seem somewhat suspicious.”

    However the tide guage series he uses shows a magnitude of variability that is absent in the more recent parts of the record where global scale sea level is measured by satellites. So it’s questionable whether the magnitude of the thermal response to the solar cycle is correct; the near land shallow water tide guage series may simply have enhanced warming/cooling response that isn’t representative of the ocean in its entirety. Additionally, Shaviv neglected to account for the volcanic contribution to cooling that is in phase with two of the solar cycles used by Shaviv (as described by Lean and Rind). That will also cause an overestimate of the apparent ocean thermal response to the solar cycle.

    That’s not to say that there isn’t an ocean thermal response to the solar cycle; there must be one. Note also that a larger response than is supported by consideration of the solar irradiance variability should arise if there is a positive cloud feedback to surface warming, which is supported to some extent by recent work (Dessler and Clement for example).

    So nothing necessarily to do with the CRF, and as for an accountably large discrepancy between the thermal response and the irradiance component of the solar cycle, I’d consider the verdict is “not proven” (as we say in Scotland).

    Comment by chris — 26 Sep 2011 @ 2:23 PM

  19. Pete,

    Good question. There aren’t really any regions of the atmosphere free of primary particles. However, some areas such as higher up in the troposphere (above a few kilometers) can have particle number concentrations that are very dominated by particles formed through nucleation. Even in some locations near the Earth’s surface nucleated particles can comprise more than 50% of the CCN.

    Comment by Jeff Pierce — 26 Sep 2011 @ 2:47 PM

  20. Dr. Pierce,

    I am a bit confused by two of your statements Here you have written “it appears unlikely to me (and most other scientists working on aerosol-cloud interactions who’ve shared their thoughts on this hypothesis with me) that this mechanism will be strong enough to greatly change clouds?” In Nature Geo Science you wrote “”Atmospheric aerosols strongly influence Earth’s climate, but how they form has remained a mystery. According to cloud chamber experiments, a mixture of vapours, as well as ions formed by galactic cosmic rays, contribute to the particle formation recipe”. How may your reader reconcile these?

    [Response: Charles, not sure what Dr. Peirce’s response would be but mine is the that these aren’t really difficult to reconcile (though I agree they seem contradictory at first glance. But the CERN experiments at best show that there is *some* influence on aerosol nucleation rates under specific laboratory conditions, but that that is a very long way from showing it matters. As we said in our previous RC post wrote in his, showing that cosmic rays matter for climate will first require showing:

    … that increased nucleation gives rise to increased numbers of (much larger) cloud condensation nuclei (CCN)

    … and that even in the presence of other CCN, ionisation changes can make a noticeable difference to total CCN

    … and even if there were more CCN, you would need to show that this actually changed cloud properties significantly,

    … and that given that change in cloud properties, you would need to show that it had a significant effect on radiative forcing.

    None of these are yet anywhere close to being shown.–eric

    Comment by Charles Messina — 26 Sep 2011 @ 2:53 PM

  21. Regarding Norman Page’s alleged cooling trends. A glance at the graphs of global temperature shows that the so-called cooling periods did not cool very much, while the warming periods showed substantial warming. This is evidence that the overall warming trend is alternately offset & amplified by a periodic climate cycle (perhaps the sun), but in now way contradicts the fact of an overall warming trend that correlates very closely to the increase of greenhouse gases.

    Comment by Dennis — 26 Sep 2011 @ 3:09 PM

  22. #17–Yep. Test for significance before pontificating, please!

    Comment by Kevin McKinney — 26 Sep 2011 @ 3:12 PM

  23. I have a question about how well the neutron monitor data reflects the ionization? According to Svensmarks hypothesis secondary mouns are most important for ionization of the lower atmosphere and though there is a very good correlation between neutron and muon count they are, as far as I understand, not quite the same?

    Comment by Bengt A — 26 Sep 2011 @ 3:19 PM

  24. MMC Norilsk Nickel, Norilsk, Krasnoyarsk Krai, Russia -Ground Zero for Arctic Sea Ice Melt/Atmospheric Forcing?



    a) North of 60 degrees lattitude.
    b) Largest SO2, HS, and CO2 emitter north of 60 degrees latitude.
    c) Major supplier of “Arctic Haze”?
    d) Close enough for Sea Breeze effect?
    e) No trees (above treeline and vegetation dead due to Norilsk being one of most polluted places on third rock from the sun).
    e) Arctic temperatures maximizing nucleation?
    f) Max Planck and NASA doing air sampling using Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container (CARIBIC) Program:

    “Source Estimation of Norilsk Nickel by CARIBIC Aircraft” by

    Comment by Gordon Jenkins — 26 Sep 2011 @ 3:28 PM

  25. Dr. Pierce,

    Thanks for posting here. I enjoyed reading your post. The following paper is being presented by some as evidence that GCRs have a notable affect on cloud cover. Do you have any thoughts?

    Comment by MapleLeaf — 26 Sep 2011 @ 4:39 PM

  26. Thank you. That was very good.

    Comment by Septic Matthew — 26 Sep 2011 @ 4:59 PM

  27. #25, MapleLeaf: Yes, that Dragic paper is fascinating. Its hard to deny from that that there isn’t something going on. Its certainly the cleanest data I’ve seen on Forbush Decreases and an environmental variable (probably because the use of surface stations allows them to include many more FDs than when using satellite data). I look forward to more research involving these techniques, and hopefully we can get some clues into the physics of what is happening.

    I do want to reiterate again that many Forbush decreases are accompanies by Solar Energetic Particle events that affect chemistry of the stratosphere, so it isn’t necessarily the cosmic rays that are driving the changes. It would be neat to see similar work to this paper where the FD events are divided into cases with and without SEP events.

    Comment by Jeff Pierce — 26 Sep 2011 @ 5:35 PM

  28. Dragic shows very clearly that FDs with a 7% reduction produces an increase in DTR. But include FDs with only a 5% reduction and the DTR increase disappears. That’s not a very robust result.

    Comment by muoncounter — 26 Sep 2011 @ 6:45 PM

  29. #28 muoncounter: This is a good point. Though with the 5% criteria there are 81 events, but only 35 events with the 7% criteria. It appears that it needs to be a big event to reach out of the noise (e.g. look at Figure 5).

    One possibility is that the biggest FDs are associated with the disproportionately big SEP events. I recently eyeballed the strong SEP events ( a list is in the auxiliary material) and they generally to correspond to the largest recent FD events ( If you look through the list of FD events in the Svensmark paper, the biggest 6 events have very large SEP events associated with them. The rest of the FD events have generally much weaker SEP events associated with them (the drop off in SEP strength is much larger than the decrease in FD strength), and about half of the remaining FD events have no SEP event listed at all in the Barnard paper. But again… we need to figure out a mechanism :)

    Comment by Jeff Pierce — 26 Sep 2011 @ 7:17 PM

  30. Dr. Pierce#29: Indeed, which makes deciphering the net effect quite a chore. University of Delaware Bartol Research has an excellent graphic of this type of compound event: FD prior to (and after) the GLE. They also list a grand total of 70 GLEs since 1942.

    Comment by muoncounter — 26 Sep 2011 @ 7:52 PM

  31. Please add SEP [Solar Energetic Particle] and GLE to the Acronym index.

    There are a lot of paywalls in the references.

    Does the fact that ammonia is an alkali and the sulfates are acids have anything to do with the effect that ammonia has? Like electrostatic repulsion?

    Comment by Edward Greisch — 26 Sep 2011 @ 10:15 PM

  32. Edward (#31): yes, the effect of ammonia is precisely due to the fact that it is a base, and thus enhances the clustering of acids. Other bases like pyridine or amines do this as well, with the strength of the effect depending on proton affinities, number of H-bonds formed, atmospheric concentration, etc. BTW, it is worth noting that while there are thousands of acidic compounds in the atmosphere, there is only a relatively small handful of basic compounds.

    Comment by Theo Kurtén — 27 Sep 2011 @ 2:37 AM

  33. #30 and #31, thanks for that graphic, muoncounter. I had seen it in the past, but didn’t know it was on the web. Edward, GLE stands for ground level enhancement, which is when a solar energetic particle (SEP) event is detected from the gound. In these cases there is an enhancement of ionization at the ground. This is often followed by the Forbush decrease in ionization in the following days. This paper has a nice overview in the discussion (

    Comment by Jeff Pierce — 27 Sep 2011 @ 4:41 AM

  34. #31, Edward: Ammonia being a base and sulfuric acid being an acid is exactly why ammonia aids in nucleation. Ammonia is attracted to the hydrogen atoms that the sulfuric acid doesn’t really want. Organic amines are similar to ammonia in this respect and also aid in nucleation. Good reasoning!

    Comment by Jeff Pierce — 27 Sep 2011 @ 4:46 AM

  35. Nice post, Jeff.

    There’s a new paper (soon) out by Agee et al “Relationship of Lower Troposphere Cloud Cover and Cosmic Rays: An Updated Perspective”

    The “near final draft” is on Curry’s blog:

    They note that there is 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, …”

    (since more GCR’s should, according to Svensmark’s hypothesis, lead to more cloudiness)

    I agree with Eli that sulfuric acid (and hence SO2 or other sulfur species such as DMS) is probably the limiting factor for nucleation in clean surroundings. In areas where more than enough SO2 is present (urban, industrial), the limiting factor may be to get the freshly nucleated particles grown to large enough sizes so as to influence the radiation budget either directly (via scattering of solar radiation) or indirectly (via acting as CCN). They may be scavenged (by bigger particles; coagulation) before they’re even noticed (most routinely used instrumentation doesn’t measure the particles until they’re larger than 3 nm in diameter).

    Comment by Bart Verheggen — 27 Sep 2011 @ 6:26 AM

  36. Thanks for that paper, Bart!

    Comment by Jeff Pierce — 27 Sep 2011 @ 7:35 AM

  37. The GCR link to cloud formation is interesting but it appears that people clinging to it as a key to AGW need constant reminding that a) there hasn’t been a trend in GCR for the last 50 years and b) that every other influence upon climate doesn’t disappear when you identify another. All the climate influences crowd in together like nursing piglets.

    Besides, if GCRs had increased enough to cause the warming of the last 50 years would we even be here to worry about it? That’s a lot of high energy particles.

    Comment by Jeffrey Davis — 27 Sep 2011 @ 9:38 AM

  38. Thank you for comments Dr Pierce

    I would like to suggest that stratospheric CCN’s can be seen, particularly at and after sunsets.
    And are relatively more common during El-Nino filling about half the high sky from the horizon.
    Not so much during La-Nina, 1/4 or less. They are seen as black streaks, perpendicular to sun rays, from the ground only seen at sunset or sunrise twilights. From the air
    well above cirrus when present, captured above cirrus while flying 35 to 39000 feet.

    Please take a look at my specially dedicated blog article :

    Comment by wayne davidson — 27 Sep 2011 @ 10:08 AM

  39. Latest papers? Ari’s is well updated.

    Comment by Pete Dunkelberg — 27 Sep 2011 @ 10:57 AM

  40. Another paper, another reminder that many organic aerosols are live organisms:
    29 July 2011
    Appl. Environ. Microbiol. doi:10.1128/AEM.05498-11

    “Bacteria are abundant in the atmosphere where they often represent a major portion of the organic aerosols…. We used high-throughput pyrosequencing to analyze bacterial communities present in the PM2.5 aerosol fraction (fine particulate matter ≤ 2.5µm) from 96 near-surface atmospheric samples collected from cities throughout the midwestern U.S….”

    Comment by Hank Roberts — 27 Sep 2011 @ 11:28 AM

  41. Jeffrey Davis,

    I believe the standard theory is that a decrease in GCRs should cause warming: A drop in GCR count reduces low cloud cover causing a decrease in Earth’s albedo.

    Comment by Paul S — 27 Sep 2011 @ 11:35 AM

  42. A wonderfully clear explanation of a complex subject.


    My Question:

    Why did it take so long to conduct a test that was proposed in 2000 by CERN scientists?

    CERN investigators submitted a proposal in 2000 for the CLOUD experiment and revised this several times … see 2004 revision.

    “The aim of CLOUD is to investigate and quantify cosmic ray-cloud mechanisms under controlled laboratory conditions using a CERN particle beam as an artificial source of cosmic rays that simulates natural conditions as closely as possible.”

    Why the delay in conducting the needed experiment?

    The costs of the tests were not that high, about $10 million US.

    Was it political opposition to Svensmark’s theory which might conflict with the concept that AGW is “settled science”.

    Search “Svensmark” on RealClimate and you get 54 hits essentially criticizing Svensmark scientific credentials, research, and lack of integrity.
    Just one example of scientific collegiality.

    RealClimate – Comments on Natural Variability and Climate Sensitivity
    … but I don’t think this is considered to be a viable hypothesis anymore, given the sloppiness uncovered in the way Svensmark et al analyzed their data. …

    Rather than personally attacking those who disagree or challenge current scientific theories, run the damn experiment that proves them wrong.

    I loved this comment by Jeffrey Pierce:

    “As an aerosol scientist, I found the results showing the detailed measurements of the influences of ammonia, organics and ions from galactic cosmic rays on aerosol formation exciting.”

    I hope we won’t have to wait another decade before we run the needed experiments that answers many of the questions and interactions that this CLOUD experiment generated.

    Perhaps RealClimate can be supportive this time.

    [Response: I don’t recall be unsupportive of the CLOUD effort, though their initial aims, predicated on taking Svensmark’s correlations at face value were not convincing. As an appartus for understanding aerosol physics they are very impressive though. However, you misjudge the criticism entirely. We have not criticised svensmark for challenging mainstream science or for proposing new ideas – both of these things are valuable. Instead, we (and specifically I) have criticised him for outrageously inflated claims, ridiculous statements, dubious and unjustified ‘corrections’ to data to fit his ideas, refusals to acknowledge that there hasn’t been a recent trend in GCR, laughable attempts to adopt the mantle of Galileo simply because his efforts have been criticised etc etc. This has nothing to do with potential mechanisms of GCR climate interactions, and everything to do with his professional conduct. It is no coincidence that Svensmark is not on the CLOUD team. I have no knowledge of process by which CLOUD got funded, but $10 million science grants don’t just get approved in an afternoon under any circumstances. – gavin]

    Comment by J Gary Fox — 27 Sep 2011 @ 12:10 PM

  43. re: 41

    I’m confused. My understanding is that low cloud cover produces warmth and high cloud cover is associated with an increase in albedo and cooling.

    Comment by Jeffrey Davis — 27 Sep 2011 @ 2:24 PM

  44. Looking at the Agee et al. draft (still to undergo copy-editing I hope), any CR-cloud correlation indeed breaks down from 2004 or so. But just a side question: I’m a bit confused about that record CR high — should it be visually obvious in their plots? ‘Cause in the Kiel plot, I don’t see it. And the missing filtering at the end of the Beijing plot makes it hard to tell.

    Comment by CM — 27 Sep 2011 @ 2:30 PM

  45. “In the midlatitudes, winter brings a substantial decline in solar heating, yet the corresponding drop in air temperature near the surface is between 70 and 80 percent less than what the decline in solar heating would seem to imply. More abundant and thicker winter clouds, with slightly higher tops, trap heat better….”

    Comment by Hank Roberts — 27 Sep 2011 @ 3:04 PM

  46. and also from
    “Low, dense sheets of stratocumulus clouds hanging just above the ocean cool more than they heat. They make efficient shields against incoming sunlight, and because they are low – and therefore warm – they radiate upward almost as much thermal radiation as the surface does. In contrast, the thin, wispy cirrus clouds, which soar at 6,000 meters (20,000 feet) and higher, reflect little sunlight, but they are so cold that they absorb most of the thermal radiation that comes their way. Hence they warm more than they cool. The net cooling effect of clouds is the sum of a large number of such specific effects, many of which cancel one another….”
    Last updated: 2009:06:03 @ 17:19:32

    Comment by Hank Roberts — 27 Sep 2011 @ 3:05 PM

  47. Very interesting article, thanks a lot.
    About GCR-cloud, I read an article on, it says: “According to Svensmark, cosmic rays seed low-lying clouds that reflect some of the Sun’s radiation back into space,..”
    In the same article Chris Folland, a climate researcher at the UK’s Met Office, is quoted: “Low-level clouds generally cool the surface climate, but it’s not clear why they should be preferentially affected by cosmic rays, given that there is some effect on overall cloudiness.”
    As I understood from Bart Verheggen’s reaction #35, the correlation between GCR and clouds is absent and the correlation with temperature is also about 0. Suppose there would be some small influence of these GCR’s, why would this influence be limited to low-level clouds that have a cooling effect ? At least the Met Office researcher seems to think otherwise and I fail to see the logic also. Am I missing something?

    Comment by Jos Hagelaars — 27 Sep 2011 @ 5:28 PM

  48. #47 Jos, you are correct. It is not clear without understanding the physics why low-level clouds would be affected more than other clouds. Though, it is certainly plausible that some clouds might be affected more than others, we need to keep digging.

    Comment by Jeff Pierce — 27 Sep 2011 @ 7:11 PM

  49. # 43

    Your understanding is backwards. Just go outside on a summer day when there’s thick cumulus right above you. The high clouds OTOH are whispier and not great visible reflectors, but they are very cold and thus the presence of high clouds reduces the local radiating temperature, making it warmer.

    Comment by Chris Colose — 27 Sep 2011 @ 8:20 PM

  50. The heliopause is the critical point. And what must also be considered is that the GCR time from heliopause to earth is a substantial lag. Secondly the background GCR also changes as we move through the galactic plane. You cannot simply hope to correlate a direct relationship between solar cycle and GCR and cloud cover – it is much more complex than that.

    Comment by Dr David King — 27 Sep 2011 @ 8:36 PM

  51. Addendum to #24, Norilsk.

    Norilsk is above Arctic Circle at 69 degrees, 20 minutes (and spare change).
    MMC Norilsk Nickel, in addition to producing SO2, HS and CO2 also provides catalysts for nucleation and chemical reactions in the form of platinum, palladium and copper nano particles.

    Norilsk, twice per year falls under the aurora borealis (auroral oval) near the equinoxes and between 11pm and 2am local time (opposite sunside) during the periods of magnetic reconnection (THEMIS Satellite).

    Is it therefore inconceivable that the pollutants from Norilsk are involved in amplified nucleation effects due to auroral inductively coupled inloading, given the heavy metal particles emitted may be charged inductively like any other conductor passing through a magnetic field?

    Does Norilsk have the potential to meet all the requirements of CERN CLOUD and all of the concerns discussed so far?

    Would it not be prudent to take atmospheric samples in the Norilsk area and downwind?

    S. Fuchs, T.Hahn, H.G. Lintz, “The oxidation of carbon monoxide by oxygen over platinum, palladium and rhodium catalysts from 10−10 to 1 bar”, Chemical engineering and processing, 1994, V 33(5), pp. 363-369

    Comment by Gordon Jenkins — 27 Sep 2011 @ 9:24 PM

  52. As a somewhat confused layman, I have a few questions trying to get past the details to the “big picture”. My apologies if these seem too simplistic, but I’m really just trying to get some perspective on all this…

    First, I assume it is not controversial that there seems to be at least a plausible causal connection from the solar wind to cosmic rays reaching our atmosphere to cloud formation to warming/cooling at the Earth’s surface.

    From this, I assume that variations in the solar wind presumably may have some (still to be determined) effect on global warming via this mechanism.

    Q1: What are the hard upper and lower bounds limiting the fraction of global temperature changes over the past century that might be attributed to variations in cosmic radiation? In particular, are 0% and 100% both plausible, or can tighter bounds be strongly supported?

    Q2: Same question, but looking forward a century?

    Q3: Same question, but looking at the past several million years?

    Q4: Is there a consensus range which most climate scientists would expect? (E.g., even if 0% and 15% are both possible, would either be surprising to most researchers?)

    Q5: Did the recent CERN results refine those ranges at all?

    Q6: Are future CERN results likely to refine those ranges?

    Thanks in advance to anyone willing to stick their neck out here… (and a pox on Captcha)

    Comment by JimCA — 28 Sep 2011 @ 12:27 AM

  53. Dr David King #49 (I’ll hazard a guess you’re not the former UK government science counselor by that name),

    We can measure cosmic radiation from Earth as it hits us, we don’t have to estimate it from the solar cycle. So complexities in the solar-GCR relationship, real or imagined, are surely not very relevant to testing the GCR-cloud connection.

    But relevant or not, please oh please do quantify the “substantial lag” from heliopause to Earth for particles traveling near the speed of light—relative to the 11-year solar cycle…

    Comment by CM — 28 Sep 2011 @ 2:36 AM

  54. #50 Gordon: This is an interesting idea. However, there are some complicating factors that make backing out cosmic ray effects from a single region (or a single plume in this case) difficult. (1) Meteorological conditions are always change and can greatly affect nucleation and growth. Thus, you’d need to focus on long-term measurements (e.g. 11-year solar cycle rather than Forbush decreases). (2) Emissions are never constant depending on the amount and composition of the ores they are smelting. My guess would be that the emissions will have much higher fractional variability than the changes in cosmic rays. Thus, measuring the changes in the 11-year cycle may have trends in emissions that may need to be corrected for, and this is not always easy. Thanks for the idea though!

    Comment by Jeff Pierce — 28 Sep 2011 @ 4:35 AM

  55. Interesting timing.

    It looks like we might be in the middle of a Forbush decrease right now…

    (note, this updates real time, so you view this in the future, it won’t show the decrease in Cosmic rays near the poles that I see.)

    There was a coronal mass ejection that just hit the Earth (

    muoncounter, you seem to know your stuff in this area. Can you weigh in on this?

    Comment by Jeff Pierce — 28 Sep 2011 @ 6:41 AM

  56. #51 JimCA: I’ll stick my kneck out a bit, but in no way would I consider myself an authority on most of the questions you are asking (Other than maybe question 5).

    Q1: Lower and upper bounds on the contribution of cosmic rays warming of past century?

    Lower bound: Essentially 0% of the warming of the past century was caused by cosmic rays. This would require us to better understand the reported correlations between cosmic rays and clouds and find that the correlations were not caused by the changes in cosmic rays (either the correlation was co-incidence or some other factor that correlates with cosmic rays [e.g. solar irradiance or solar energetic particle events] contributed to the changes in clouds). Furthermore, we’d need to show that the proposed physical mechanisms are weak.

    Upper bound: The cosmic ray flux decreased by about 5% between 1900-1950 (Carslaw et al., Science, 2002), but has not significantly changed since then. Thus, even in a case where cosmic rays do strongly affect clouds, they could only have greatly contributed to the early-20th century warming (~1/3 of the warming of the past century). The absolute upper bound would be a bit lower than this since GHGs were increasing during this period (albeit more slowly than recently). Thus, my best guess upper bound would be 25-30%. This would require us to (1) show in the mechanisms that cosmic rays very effectively change clouds, (2) show why cosmic rays don’t always correlate with cloud cover in observations, and (3) why the effect of changes in cosmic rays on clouds were so much bigger than the changes in human-generated aerosols (which increased very quickly in the first half of the 20th century) on clouds. This last point has always irked me a bit… we REALLY gunked up the atmosphere with particles.

    Q2 and Q3: The next century and past climates. I’m not an expert on the predictions of cosmic rays in the future or retrodictions of cosmic rays in the past. But it seems plausible that cosmic rays may have been a player in past climate changes. I really don’t have much knowledge here though.

    Q4: Consensus range for scientists. Speaking for others is the easiest way to get into trouble. Probably better to have an expert elicitation. I will say that most (though not all) aerosol and cloud physicists that I’ve spoken with think that the clear-sky mechanism (described in the post) is too weak to account for important changes in clouds. This research is my main area of focus, so I’m a bit more comfortable speaking on this.

    Q5: Do the CERN results refine those ranges at all. No. Certainly not the upper and lower bounds. As I said in the post, they have only touched on one part of clear-sky mechanism, and their results regarding cosmic rays are similar to previous results (their real advancements came by showing the chemical species in the nucleating cluster).

    Q5: Are the CERN results likely to refine those ranges? I hope so. I know this is their plan. We’ll see what they do. :)

    Comment by Jeff Pierce — 28 Sep 2011 @ 8:49 AM

  57. re: 49

    Thanks for the clarification. I believe my understanding on this has always been influenced by getting sun-burned on cloudy days when I was a kid.

    Comment by Jeffrey Davis — 28 Sep 2011 @ 8:59 AM

  58. #20 Charles: Sorry for the slow response. I wrote one earlier, but it doesn’t appear to have posted properly. In my statement in this post, I was saying that 5-20% changes in cosmic rays appear unlike to change cloud cover by several percent through the clear-sky mechanism. In the Nat Geo article I was stating that ions from cosmic rays do make it more favorable for 1 nm particles to form. This does mean that there will necessarily be large changes in clouds from changes in cosmic rays.

    Thanks for the inline comment, Eric!

    Comment by Jeff Pierce — 28 Sep 2011 @ 9:07 AM

  59. Is it just the ionisation process which needs to be considered or can GCR’s have another effect?
    Quotes from above link:-
    While looking for climatic factors that might influence the growth of the trees, they made the surprising discovery that the trees grew faster in a pattern that matched with cycles of galactic cosmic rays;
    Plant physiologist and tree growth expert David Ellsworth, at the University of Western Sydney, in Australia, said it was an “intriguing phenomenon”, and that the hypothesis that the growth spurts were caused by diffuse radiation driven by galactic cosmic rays, was “reasonable”.
    I too think this may be a reasonable hypothesis and worthy of consideration.
    The study, published in the journal New Phytologist looked at the factors that influence the growth of Sitka spruce trees (Picea sitchensis) felled in the Forest of Ae in Dumfriesshire, Scotland.
    This particular tree species produces high amounts of BVOC’s, isoprene and monoterpines which can act as precursors for the formation of c.c.n.. Anything which promotes plant growth promotes the production of some addition material for cloud droplet formation, which must contribute to cloud formation and climate change.
    So we have Co2 enrichment , GCR , and then this;-
    If ocean plants are fertilised don’t they produce more DMS?
    This all seems to add to the factors which need to be accounted for when trying to establish the origins and actions of aerosols.

    Comment by wush — 28 Sep 2011 @ 9:11 AM

  60. Jeff Pierce – The range of station responses on that graphic is interesting. I thought it might be regional but, presuming ‘Newark’ refers to New Jersey, there doesn’t seem to be a well-defined pattern. Incidentally is there any reason why the Tibet record is much ‘cleaner’ than the others? Related to altitude?

    A completely different question: There seem to be a range of factors, relating to the composition of the atmosphere, which determine whether or not, and to what extent, GCRs can ultimately affect cloud formation. Is it possible that human emissions are changing atmospheric conditions in such a way that GCRs are more (or less) likely to have an effect?

    Comment by Paul S — 28 Sep 2011 @ 9:12 AM

  61. Hi Jos (47),

    Your question of why specifically low clouds would be affected by cosmic rays was addressed by Yu et al ( ) and I described it in an earlier RC post on cosmic rays and aerosol nucleation ( ):

    “Based on his model for ion induced nucleation, Yu found that at low altitude, the number of particles produced is most sensitive to changes in cosmic ray intensity. At first sight, this may be a surprising result in light of the increasing cosmic ray intensity with increasing altitude. The reason is that high aloft, the limiting factor for particle formation is the availability of sulfuric acid rather than ions. Above a certain GCR intensity, increasing ionization further could even lead to a decrease in ion induced nucleation, because the lifetime of ion clusters is reduced (due to increased recombination of positive and negative ions). In contrast, at low altitude particle formation may be limited by the ionization rate (under certain circumstances), and an increase in ionization leads to an increase in nucleation. “

    Comment by Bart Verheggen — 28 Sep 2011 @ 10:12 AM

  62. For Jeff Pierce (or Gavin?) — Jeff above mentioned a possible Forbush event happening right now — can you capture the picture at (quickly before it updates) — for reference? Right now it shows the last few hours of Sept. 18th. (Or point to an archive if there is one). Seems like an area discussion will want to refer to again.

    Comment by Hank Roberts — 28 Sep 2011 @ 10:55 AM

  63. Dr Pierce @ 58 Your comment ends with “This does mean that there will necessarily be large changes in clouds from changes in cosmic rays.”

    Is that as intended?

    Comment by Pete Dunkelberg — 28 Sep 2011 @ 11:38 AM

  64. Jim CA, re: bounding the possible effect of cosmic rays,

    Just as a coda to what Jeff Pierce said above, Erlykin et al. (2011) calculated a possible cosmic-ray contribution of 0.002 °C to the warming of the past 50 years.

    I’m sure they did this in all seriousness. I mean, I’m sure both the authors and the peer reviewers of the Journal of Atmospheric and Solar-Terrestrial Physics frown on the frivolous calculation of insignificant effects for sarcastic effect. But I still think it’s a funny way to say “no trend, no role”.

    Comment by CM — 28 Sep 2011 @ 12:05 PM

  65. Thanks Bart for your answer in #61. I wasn’t aware of your posts here on RC, but will read them this evening. See you on

    Comment by Jos Hagelaars — 28 Sep 2011 @ 12:09 PM

  66. #63 and #58: I meant to say, “this does NOT mean”, thanks Pete!

    Comment by Jeff Pierce — 28 Sep 2011 @ 12:50 PM

  67. Looking at the link for Erlykin et al. the abstract sorts it out a bit:

    “… for the troposphere there is only a very small overall value for the fraction of cloud attributable to cosmic rays (CR); … probably ∼1% for clouds below ~6.5km but less overall. The apparently higher value for low cloud is an artifact.

    The contribution of CR to ‘climate change’ is quite negligible.”

    Comment by Hank Roberts — 28 Sep 2011 @ 1:42 PM

  68. #62, Hank: Here is the frozen plot:

    Comment by Jeff Pierce — 28 Sep 2011 @ 2:23 PM

  69. J Gary Fox #42

    It is not uncommon in high energy particle physics for projects to take years to get funded, researched, designed and built. They could not have started taking real data until the LHC’s main beam was up and running stably (Sept 2008). Just look at the number of co-authors on Kirkby’s Nature paper; getting that many physicists to sit still long enough to agree on just the paper’s title could take months.

    No need looking for ‘political’ reasons.

    Comment by muoncounter — 28 Sep 2011 @ 3:48 PM

  70. muoncounter – I don’t think the CLOUD experiment used the LHC. The supplementary information says they used something called the Proton Synchrotron.

    Comment by Paul S — 28 Sep 2011 @ 4:59 PM

  71. You’re right. The Proton Synchrotron is part of the proton injector series for the LHC, effectively a medium energy ‘pre-accelerator’ stage. Substantial refitting was done on this older machine prior to LHC comissioning.

    CLOUD was approved and ran prototype testing in 2006 (see this 2007 status report and Duplissy et al 2010). That meant the earliest beam time they could get was 2007-2008. It was actually 2009 before CLOUD started taking data runs with the PS secondary beam.

    There is, as usual, no evidence of any ‘political attempt’ to slow the project. Rank speculation may get you somewhere on some blogs, but not here.

    Comment by muoncounter — 28 Sep 2011 @ 8:42 PM

  72. I downloaded GCR(neutron) data from [1], TSI anomaly data from [2], and HadCRU T anomaly(using the Defreitas et al “trick” of detrending) data from [3]. All data sets are monthly, and start in 1978.83. I normalized the pressure corrected GCR data by dividing by the average, and subtracting 1 from the results to create an anomaly series. Plotting TSI versus GCR yields a scatterplot with the expected negative correlation; GCR = -0.11*TSI, R^2=0.56. Plotting TSI versus HadCRU T yields a weak positive correlation; HadCRU T = 0.07*TSI, R^2=0.07. Since there is a negative correlation between TSI and GCR, there is also a negative correlation between GCR and HadCRU T; HadCRU T = -0.31*GCR, R^2=0.03. How do we sort out whether the temperature changes are driven by TSI, GCR, or a combination of the two?

    In the scatterplot of TSI versus GCR, there is not a perfect correlation – there are months when TSI anomaly and GCR anomaly are high, and months when TSI and GCR are both low – points in the first and third quadrants of the graph. There are 70 months when this is the case, from a span of 393 months. The TSI anomaly for these months ranges from -0.57 W/m^2 to 0.56 W/m^2, the normalized GCR anomaly ranges from -0.12 to 0.07 (-12% to +7%). The detrended and offset HadCRUT anomaly ranges from -0.37 to 0.36 degrees C.

    I isolated these months TSI, GCR, and HadCRU T, and looked at the correlations. Because I’ve restricted the data to those months when the TSI and GCR are positively correlated, that correlation is meaningless; however, if one looks only at TSI and GCR are both positive, or when both are negative, there are negative correlations; GCR = -0.02*TSI+0.03, R^2=0.02 when both are positive, GCR = -0.09*TSI – 0.06, R^2=0.2 when both are negative.

    Now, let us suppose that GCRs have a strong effect, causing most of the variation in global temperature by modulating clouds with the solar cycle. If the effect of GCR is dominant, the months when the GCRS are high, even when the TSI is high, temperatures should be lower; and when the GCRs are low, Temperature should be higher, even with lower TSI. Plotting HadCRU T versus TSI, only months when the TSI and GCR anomalies have the same sign yields a positive slope; HadCRUT = 0.11*TSI + 0.01, R^2=0.04. Plotting HadCRUT versus GCR gives a positive slope as well; HadCRU T = 0.62* GCR +0.01 for the full 70 months. The slope coefficient for the 20 months with the lowest GCR anomaly is -1.77, but the coefficient for the 20 months with the highest GCR anomaly is 3.76. Since the slopes for both TSI and GCR versus HadCRUT are positive, I conclude that although decreasing GCRs may enhance warming from concurrent increases in TSI, and vice versa, which is normally the case since they move in opposite directions, the influence of changes in TSI are the dominant factor. The negative correlation of GCR and temperature when the GCRs are negative, but overall positive correlation when both signs are analyzed may indicate a nonlinear effect, with stronger influences for decreasing GCR (such as the limited number of Forbush Decreases available for analysis).

    Wouldn’t all clouds over snow covered ground be warming, since the albedo is already high? And wouldn’t the increase in amplitude of variations of GCR with latitude (increasing towards the poles, where snow cover is common) tend to negate warming from low clouds near the equator because of this effect? Also, since the infrared radiation from the ground has a Lambertian distribution with its maximum intensity perpendicular to the surface, but the solar illumination is near parallel rays from the sun, a given cloud area at high latitudes will capture the same amount of outbound infrared, but reflect a smaller portion of the incoming solar radiation; at some angle where the sun is low on the horizon, this should cause low clouds to be warming.


    Comment by Brian Dodge — 29 Sep 2011 @ 3:09 AM

  73. Hank #67, yes, bounding the fraction of cloud cover attributable to cosmic rays was the thrust of the Erlykin et al. paper, and I should have mentioned it, instead of trying to be funny.

    As for their calculation of the possible contribution of cosmic rays to global warming, it is unsurprisingly negligible for the posited 0.6% change in the mean intensity of cosmic rays over the past 50 years. It would be interesting to do the same estimate for the first half of the 20th century, though, given the 5% change Jeff Pierce mentioned above.

    Comment by CM — 29 Sep 2011 @ 3:40 AM

  74. J Gary Fox is suspicious about the relatively long time it took before the cloud study was conducted. “Why the delay in conducting the needed experiment? The costs of the tests were not that high, about $10 million US.”

    That’s actually a pretty large price tag, and there’s a lot of competition for funds at that level. I was recently on a review panel evaluating approximately 60 proposals in the $3 million-$6 million range. The proposals had already been screened once, so these 60 represented just the good ones. Going into the panel, we were told that the agency would probably be able to fund 2 or 3 of the 60. As it turned out, there were so many good proposals in that group that the agency did some soul-searching and managed to come up with funds for 4-5 of them.

    In general, the question “how come proposal X hasn’t been funded?” is not a very useful question. Lots and lots of good proposals don’t get funded. It doesn’t mean there’s some conspiracy at work.

    Comment by J — 29 Sep 2011 @ 9:59 AM

  75. It doesn’t mean there’s some conspiracy at work.

    Not to mention that the notion that Gavin, working as a modeler at NASA GISS, could have a substantial impact on the research program and funding priorities at a high-energy experimental facility like CERN, with its many european collaborators involving a large percentage of the experimental physics community and a bunch of high-profile research groups, is rather ludicrous on the surface …

    Comment by dhogaza — 29 Sep 2011 @ 11:55 AM

  76. Jeff Pierce#55: Sorry for the slow response. Yes, the sun’s been spitting flares in the past week — see for details, as well as stunning aurora photos. The current FD seems to have bottomed at -5% (from Oulu’s neutron monitor current records); from the Dragic et al results, that’s not enough to make a measurable change in DTR.

    Comment by muoncounter — 29 Sep 2011 @ 9:38 PM

  77. #72, Brian Dodge: Thanks for this analysis. Yes, it appears difficult to find connections between GCRs and temperatures in recent decades.

    I do think you are right that all clouds over snow will generally warm (there may be some exceptions to this depending on how “dirty” or how thick and aged it is). Interestingly, although the poles have the biggest fluctuations in cosmic rays, Marsh and Svensmark (2003) reported the biggest cloud changes with the 11-year solar cycle to be in midlatitude marine straticumulus clouds (although they did have a controversial correction to the ISCCP cloud data used in this paper in order to maintain the 11-year solar cycle).

    Comment by Jeff Pierce — 30 Sep 2011 @ 4:03 AM

  78. Nice article Jeff.

    What I’d like to see is a sensitivity calculation of particle nucleation and growth to all the variables that could affect it. It’s a very nonlinear process (or processes), strongly dependent upon sulfuric acid concentration, temperature, and the trace “contaminants”, as shown in the CLOUD study. But one of the primary controlling factors is preexisting particle surface area, which scavenges condensable gases before they have a chance to form new particles. And this surface area is largely governed by cloud formation and precipitation, which effectively removes particles to the surface, leaving very clean air behind. In my observations flying around the free troposphere, it is these regions, where preexisting particles have been scavenged, that are most likely to have newly formed particles present (other than concentrated industrial or urban plumes). So I have a hard time seeing how GCRs, which produce the ions that assist nucleation, play a controlling role when all these other processes are in play. Where rain/snow effectively scavenges the preexisting particles, nucleation tends to proceed; where it doesn’t, nucleation is more rare. At least in the free troposphere; there’s certainly a lot of evidence for nucleation occurring regularly over forested regions and in urban areas. But in these cases (e.g. the Finnish work) ion-mediated nucleation usually doesn’t dominate.

    Your thoughts?

    Comment by cbrock — 30 Sep 2011 @ 10:10 AM

  79. #78, cbrock: Thanks, Chuck! You definitely have a very informed perspective on aerosol nucleation and growth, so I’m glad you weighed in here. You are right that the global models that researches like me use don’t capture the nucleation near cloud outflow. I’ve always been curious about how important the near-cloud nucleation is for predicting aerosol indirect effects. It seems that Jan Kazil is making a serious attempt to look at this now with Graham Feingold. It would be nice if the 4 of us (and anyone else interested) could all chat when I’m in Boulder in November, especially since Jan is also an expert on ion-induced nucleation.

    My quick thoughts on your comment: I think you’re right that the 5-20% change in ion formation rate will play a secondary role to cloud scavenging in controlling nucleation near clouds (and then you still have issues with dampening in the nucleation-CCN-cloud connection). Furthermore, I think there might be a negative feedback loop for the effect of cosmic rays on near-cloud nucleation. An increase in cosmic rays would slightly increase nucleation, which would slightly increase CCN, which could slightly reduce precip, which would reduce aerosol removal, which would decrease nucleation. This is oversimplifying things, but its something to think about. I’m sure Jan and Graham would have more informed thoughts on this :)

    Comment by Jeff Pierce — 30 Sep 2011 @ 12:51 PM

  80. #60, Paul S: Sorry I forgot to respond before. Regarding your first set of questions about the various measurement sites, I don’t know for sure. I am not an expert on the cosmic ray measurements. muoncounter, can you weigh in here?

    Regarding your second question, yes, human emissions can definitely change the ability of cosmic rays to affect clouds. There are two basic competing effects (and some other complicating factors that I won’t touch on here): (1) Human-generated SO2 emissions have increased the amount of H2SO4 that forms in the atmosphere. The H2SO4 can increase the sensitivity of nucleation rates to cosmic rays and can increase the rate at which nucleated particles grow to become CCN. (2) Humans have increased the total amount of aerosol in general, so CCN concentrations are much higher. This reduces the sensitivity of CCN to changes in nucleation. Thus, the effect of cosmic rays on clouds through the clear sky mechanism may be different during pre-industrial times compared to today. However, my calculations show that there is a low sensitivity in both time periods.

    Comment by Jeff Pierce — 30 Sep 2011 @ 1:04 PM

  81. this has been a good thread. my thanks to all.

    Comment by Septic Matthew — 30 Sep 2011 @ 4:33 PM

  82. Yes, I agree with Matthew. Thanks everyone for great comments, questions and thoughts!

    Comment by Jeff Pierce — 30 Sep 2011 @ 6:47 PM

  83. Also, thank you Gavin for inviting me to write the post!

    Comment by Jeff Pierce — 1 Oct 2011 @ 8:28 AM

  84. To Jeff Pierce and comments:

    Excellent presentation of cosmic ray/cloud connections. Informative, challenging, and in the case of #69-#71….entertaining, said with tongue firmly in cheek.

    Comment by lucien locke — 2 Oct 2011 @ 6:35 AM

  85. Re the Dragic et al. paper.
    Most important issue is that there is no 1:1 relation between clouds and DTR. Sure, clouds have an important contribution to DTR, but there are other factors (only mentioned by Dragic). I used the data for a nearby station (Eelde, the Netherlands): only about 40% of the variation in DTR is ‘explained’ by variation in clouds.
    To calculate significance ‘t-statistics’ were used. Using data for Eelde, I found that for this station there is a random 29% chance to get 35 dates where the mean of DTR[d+4] – DTR[d] is greater then 0.38°C.
    Minor: the stations used in the paper are from Greenland to East-Siberian in the far east; a little bit more then European.

    Comment by HenkL — 4 Oct 2011 @ 7:04 PM

  86. Richard Alley, during his 2009 AGU Bjerknes Lecture, pointed out that paleoclimate records provide a test of the hypothesis that cosmic rays are a significant influence on climate.

    He said 40,000 years ago the Earth’s magnetic field weakened in what is called the Laschamps anomaly, to about 10% of its current level, which allowed large amounts of cosmic radiation to enter the planetary system.

    He displayed this chart

    A video of his lecture is here:
    The section of his lecture where he discusses this issue starts around minute 42:05 in the video.

    Quoting from his lecture: “its a really interesting hypothesis. There’s really good science to be done on this. But we have reason to believe its a fine tuning knob…. …We had a big cosmic ray signal [points to the chart] and the climate ignores it. And its just about that simple. These cosmic rays didn’t do enough that you can see it.”

    Comment by David Lewis — 10 Oct 2011 @ 9:07 PM

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