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  1. This is an excellent summary of the state of research in this area — or at least it appears so to this interested layman.
    The tone and level of detail are appropriate, and the links very useful.
    You may want to modify the story heading and subhead, both of which have “cosmic galactic rays” instead of “galactic cosmic rays.”

    Response: Thanks. Done. – gavin

    Comment by jre — 10 Dec 2004 @ 2:53 PM

  2. GCR may or may not be involved in cloud cover/climate, but fact is that there still is a high correlation between cloud cover (and thus temperature) and solar activity. Probably by changes in jet stream position, due to changes in UV absorption in the stratosphere.

    See: http://folk.uio.no/jegill/papers/2002GL015646.pdf

    Figure 1.
    Temporal variations from 1983â??1999, after removal of annual cycle in cloud cover data. (a) Black curve: Galactic Cosmic Ray Flux; Red curve: Solar Irradiance; Green curve: IR-Low Cloud Cover.
    Significance level of correlations: 67% for cosmic rays and low clouds, 98% for solar irradiance and low clouds. (b) Black curve: Galactic Cosmic Ray Flux; Red curve: Solar Irradiance; Green curve:Daytime Low Cloud Cover.
    Significance level of correlations: 30% for cosmic rays and low clouds, 90% for solar irradiance and low clouds.”

    Further, the sun cycle induces relative large changes in cloud cover in the US, see: http://www.gsfc.nasa.gov/topstory/20010712cloudcover.html

    And for Boston in particular: http://www.erh.noaa.gov/box/effects.htm

    The US and Boston figures are for mid-latitudes, tropical trends are opposite…

    Comment by Ferdinand Engelbeen — 12 Dec 2004 @ 7:14 AM

  3. Are you sure that the live links in the “References” section are working… I only get 404 errors!

    Response: Thanks for the heads up. We found, and fixed, one broken link. -mike

    Comment by Francis Massen — 12 Dec 2004 @ 6:59 PM

  4. Further, the sun cycle induces relative large changes in cloud cover in the US, see:

    I think he means “correlates with” cause and effect whilst likely are v. difficult to establish.

    Comment by Edward Teague — 17 Dec 2004 @ 8:01 PM

  5. I should add (after looking at the references he gives)that of course the US covers about 3.5% of the Earth’s surface and that Boston is slightly less than that.

    I speak of area not political influence or cultural history.

    Comment by Edward Teague — 17 Dec 2004 @ 8:09 PM

  6. The three references look at three different levels: global, regional and local. On all three levels there is a significant correlation between the sun cycle and cloud cover, less by GCR than by irradiation. For cause and effect: You never know, but I don’t think that cloud cover regulates the sun cycle… Globally, the variation of cloud cover during a sun cycle is around 2%, which can have a substantial influence on global temperatures.

    Page 3 of http://folk.uio.no/jegill/papers/2002GL015646.pdf gives a possible explanation for the influence. Further, the solar signal can be seen in the sea surface temperature of the oceans, the amplitude of the solar signal can be as much as 0.3 K for some solar cycles.

    For the tropics even higher: from http://www.aero.jussieu.fr/~sparc/SPARC2000_new/OralSess2/Hood/Node2.html :
    “During the past several years as the solar UV flux has increased toward the next solar maximum, the mean tropical temperature has also increased significantly by more than 0.5 K. An increase of similar magnitude occurred between 1986 and the 1990 solar maximum. These temperature increases can not be attributed easily to volcanic influences and are most probably solar in origin.”

    0.5 K for the tropics in only four years…

    Comment by Ferdinand Engelbeen — 18 Dec 2004 @ 11:58 AM

  7. In addition to my comment in #6, there is a recent investigation of different chemicals content in Antarctic ice cores, that makes a connection between solar variability and climate, in this case for wind speed around Antarctica. See: http://www.spaceref.com/news/viewpr.html?pid=15758

    That solar output has increased in the second halve of last century is confirmed by satellites: http://www.space.com/scienceastronomy/sun_output_030320.html . Although the direct heat increase is not enough to cause much climate change, the indirect influence of solar activity on cloud cover, wind and rain patterns may be large enough to have an important impact.

    Further, Svendsmake still defends his theory about the GCR-temperature connection, see:
    http://www.estec.esa.nl/wmwww/wma/spweather/Alpbach2002/Friis-Christensen.pdf

    Comment by Ferdinand Engelbeen — 1 Jan 2005 @ 5:43 AM

  8. Response to point 7: Your comment is interesting and I don’t think that we can resolve the issue here. The data in question here have all been synthesised from several satellite missions of which all show large differences in the actual level of solar output. At least one long-ish records (starting from the late 1970s) of the solar output (total solar irradiance, TSI) may indicate higher level of TSI in the last solar minimum in 1996 compared to that in 1986. Others TSI reconstructions do not indicate any such ‘trends’ (one may argue whether the difference between two such points consititutes a trend). It is interesting to note that there is a significant correlation between the TSI and the (Wolf) sunspot number. One critical point is then: if there is a trend in the TSI, why isn’t there one in the sunspot number? Furthermore, why isn’t there a trend in the GCR, which also follows the solar activity? And if there is a disagreement between the trends in TSI and the sunspotnumber, is it then justifiable to use the sunspot number or isotope records (that follow GCR) to reconstruct the TSI for paelo-climatic studies? The implications of such disagreement are quite profound, and I believe we may be looking at a very interesting topic for future research.

    I must admit that I don’t understand how Svensmark can explain how GCR can explain the recent global warming if there evidently is no trend in the GCR (Even in his own papers, the GCR records have been plotted, and they do not exhibit trend!). I think we should leave it up to Svenmark to explain this.

    Comment by rasmus — 3 Jan 2005 @ 5:04 AM

  9. In response to #8, indeed it seems to be difficult to have a clear picture of how the sun’s acticity best is described. Although all indications like sunspot (group) number, sun cycle length, TSI, AA index, GCR, 10Be, 14C all have a good correlations with each other on long term, short term differences make it rather difficult to decide what is the best indication for the sun-earth climate connection.

    Fact is that if there is a connection between solar activity (whatever by what mechanism) and cloud cover, then the small change in TSI of ~0.1% (1.3 W/m2 at the top of the atmosphere, halve of that absorbed at the surface) within a sun cycle (~0.25% or 4 W/m2 TOA on long term since the Maunder minimum) is increased with 2.8 W/m2 (2% of the ~140 W/m2 reflected by clouds) or ~7 W/m2 since the Maunder Minimum. That is some factor 4-5 over the original insolation alone, which is incorporated in current climate models…

    Response: Two points. First the radiative forcing of clouds is not just in the short wave, and depending on where they are, that can either be positive or negative. Secondly, if the potential cloud response is related to changes in circulation caused by the TSI or an ozone related change, then it isn’t an extra forcing at all – it is part of the feedback, and should already be incorporated in models. Only if the cloud change is directly forced by some cosmic ray induced process would this be an extra forcing, however, the physical evidence so far of an actual mechanism for this is underwhelming. – gavin.

    Comment by Ferdinand Engelbeen — 4 Jan 2005 @ 10:26 AM

  10. Gavin,

    Thanks for the response. As far as I know, but please correct me if I am wrong, current models include solar only/mainly as insolation alone. And consequently, cloud responses of the models are included in the same way for GHG warming as for solar warming.
    But solar has its highest direct influence in the tropics vs. GHGs more toward higher latitudes. And the highest variation of solar is in the stratosphere vs. GHGs in the lower troposphere.

    According to http://folk.uio.no/jegill/papers/2002GL015646.pdf
    “A physical mechanism connecting solar irradiance and low clouds might contain the following components: (1) Over the solar cycle the flux of ultraviolet (UV) radiation varies by several %, and even more so in the short wavelength component of the UV. This affects the propagation of planetary waves from the troposphere to the stratosphere, which in turn affects weather patterns in the troposphere [Haigh, 1996], including the strength and location of the summertime subtropical highs. Since the subtropical oceans are favoured regions for low clouds (Figure 2), especially in summer, such changes in weather patterns may conceivably affect low cloud cover in the manner seen in Figure 1.”

    Thus this is a direct negative feedback of (cooling) low clouds on solar changes in the stratosphere, not possible for CO2 (but may be partly applicable for other GHGs like methane, if they reach the stratosphere).

    The second possibility, as feedback to higher sea surface temperatures, seems also more sensitive for solar in the tropics than for GHGs in the higher latitudes…

    [Response: The point about the solar effect (through variation in the UV emission) on the stratosphere is an aspect of the solar-terrestrial link that I personally find most interesting. It is perhaps in the stratosphere (upper atmosphere) that we see the strongest signatures of the solar cycle. There have been published some papers by Shindell, Haigh and others that are worthwhile reading. When putting this in context with the recent global warming, then there seems to be some sticky points, namely that one would expect that an intensification in the UV emission (due to a more active sun) would result in a warmer stratosphere - not? There are empirical evidence for the exact opposite - a cooling stratosphere (Why does the stratosphere cool when the troposphere warms?). I think it's also fair to say that the ozone-related processes are strongly contaminated by other factors, such as man-made chemicals (CFCs and the 'ozone hole'). -rasmus]

    Comment by Ferdinand Engelbeen — 4 Jan 2005 @ 3:17 PM

  11. Please explain what the aa index is!

    [Response: Sorry! The aa-index is a magnetic activity index, and the reference to this is Mayaud, P.-N. (1972): The aa Indices: A 100-year series characterizing the magnetic activity. Journal of Geophysical Research, vol 77(34) 6870-6874. It is derived from from magnetic measurements near each of the poles (Greenwich and Melbourne observatories but superseded by observations from Abinger-Hartland and Toolangi). See also paper by Lockwood et al. and the site by J.H. Allen. rasmus-]

    Comment by Mats Almgren — 5 Jan 2005 @ 7:34 AM

  12. Rasmus,

    Takk for din reaksjon. I had the same thoughts about the change in temperature of the stratosphere. But despite the stratospheric cooling, the fingerprint of solar influences still is similar as in the past, until now. Maybe it is not the height of the stratospheric temperature which is important, but the temperature differences between the equator and other regions. For the general cooling of the stratosphere by increased GHGs in the troposphere, that may be less important. For the ozone depletion by CFC’s, that is relative highest near the poles. That should increase poleward flows in the lower stratosphere/higher troposphere. See: e.g. http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v382/n6592/abs/382616a0.html . But http://www.amath.washington.edu/research/articles/Tung/journals/interannual.pdf doesn’t support any change in planetary waves in recent decades (at least not in early winter)…

    How that relates to solar activity, with highest changed in the tropics remains to be seen…

    Comment by Ferdinand Engelbeen — 5 Jan 2005 @ 10:58 AM

  13. GCR’s, Clouds, and Climate, Oh My!
    If you were at a BBQ with a group of atmospheric scientists, and wanted to raise some hackles, there are several subjects that are notoriously easy to get people riled up… …Talk of Hockey Sticks, Inhofe, Crichton, Coulter, and you’re …

    Trackback by Head in a Cloud — 31 Jul 2006 @ 6:36 PM

  14. [...] DENIAL CLAIM #11: Cosmic rays (very high energy particles) striking the Earth’s atmosphere is the cause of global heating (Source: distillation of multiple people’s claims at Wikipedia.org). Debunking: According to this theory, cosmic rays are responsible for cloud cover – fewer cosmic rays means fewer clouds and less cooling in the summer (clouds reflect the energy) and more heating in the winter (as clouds hold heat in). Unfortunately, there doesn’t appear to be any statistically significant trend in the number of cosmic rays hitting the Earth, and the few experiments performed to date appear to be stricken with error or a failure to address key points. This could be an aggravating factor, but is highly unlikely to be the primary source of global heating. (Sources: No Link Between Cosmic Rays and Global Warming, Cosmic Rays and Global Warming, Recent Warming but No Trend In Galactic Cosmic Rays) [...]

    [Response: The interesting thing is that even if there is a decline in the high-energy GCR flux, then there is no trend in the GCR with more moderate energies on which Svensmark based his analysis and hypothesis. Thus, these moderate-energy GCRs should still be able, according to Svensmarks hypothesis, maintain a low cloud cover, regardless of the behaviour of the high-energy particles. Alternatively, the moderate GCR flux somehow ceases to influence the low cloud cover :-) -rasmus]

    Pingback by Anti-global heating claims - a reasonably thorough debunking « Scholars and Rogues — 23 Jul 2007 @ 10:21 AM

  15. [...] ray flux is of course appealing. (There is a useful explanation here, and some informed criticism here) There is a small chance that this completely explains climate change, but mostly it just adds a [...]

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    Pingback by Scholars and Rogues » Anti-global heating claims - a reasonably thorough debunking — 27 Nov 2007 @ 4:49 PM

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  18. [...] correlated with the solar cycle) has any significant impact on recent trends in global climate, see here and here and here. The other issue is that the actual mechanism for forming clouds via cosmic ray [...]

    Pingback by Cosmic Rays make clouds? - Bad Astronomy and Universe Today Forum — 11 Feb 2008 @ 1:54 PM

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    Pingback by Climate Change in Media: HT Reaches New Low « What’s with the Climate? — 6 Jul 2008 @ 5:35 PM

  23. [...] DENIAL CLAIM #11: Cosmic rays (very high energy particles) striking the Earth’s atmosphere is the cause of global heating (Source: distillation of multiple people’s claims at Wikipedia.org). Debunking: According to this theory, cosmic rays are responsible for cloud cover – fewer cosmic rays means fewer clouds and less cooling in the summer (clouds reflect the energy) and more heating in the winter (as clouds hold heat in). Unfortunately, there doesn’t appear to be any statistically significant trend in the number of cosmic rays hitting the Earth, and the few experiments performed to date appear to be stricken with error or a failure to address key points. This could be an aggravating factor, but is highly unlikely to be the primary source of global heating. (Sources: No Link Between Cosmic Rays and Global Warming, Cosmic Rays and Global Warming, Recent Warming but No Trend In Galactic Cosmic Rays) [...]

    Pingback by To Be or Not to Be » Anti-global heating claims - a reasonably thorough debunking — 27 Jul 2008 @ 3:21 PM

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