Do clouds disappear? (4)

Climate Change – News and Comments

Falsification tests of climate hypotheses

Warmer days and cooler nights when cosmic rays are scarce

Here’s a reminder of a climatic footnote to the 9/11 terrorist attacks on New York and Washington DC, ten years ago this weekend. With civilian aircraft grounded for three days, and without the contrails that usually criss-cross the skies of the USA, the difference between daytime and night-time temperatures at the surface increased. (See the Travis reference below.) Apparently like many other clouds (not all) the contrails reduce sunshine during the day and blanket the loss of heat at night. Take away those man-made clouds and the days become a little warmer and the nights a little cooler. In the jargon: the diurnal temperature range (DTR) increases.

(((Remark added 11 September. With comments coming in that cast doubt on that contrail story, I’ll repeat part of what I said in reply to Dahuang below. It doesn’t really matter what the reason was, for the post-9/11 increase in DTR, as long as everyone accepts that a loss of cloud was involved.)))

An echo of that mini-climatic event comes with the news that the DTR in Europe increases when there’s a big reduction in cosmic rays arriving at the Earth. With the implication that the skies are less cloudy at such times, it’s strong evidence in favour of Henrik Svensmark’s hypothesis that cosmic rays help to make clouds. The report comes from Aleksandar Dragić and his colleagues at the Institute of Physics in Belgrade. I’m grateful to Bengt Andersson for drawing their paper to my attention. It was published on 31 August and the full text is available here  It’s typical of the pathetic state of science reporting that I still seem to have the story to myself ten days later.

More than a year ago I began a succession of posts on whether or not observations in the real world support or falsify the Svensmark hypothesis. The most explanatory was the first – see

The focus was on the “natural experiments” in which big puffs of gas from the Sun block some of the cosmic rays coming from the Galaxy towards the Earth. The resulting falls in cosmic ray influx, called Forbush decreases, last for a few days. The game is to look for observable reductions in cloudiness in the aftermath of these events. The results are most clearly favourable to the Svensmark hypothesis for the Forbush decreases with the largest percentage reductions in cosmic rays. Scientists keen to falsify the hypothesis have only to mix in some of the weaker events for the untidiness of the world’s weather to “hide the decline”.

The Serbs avoid that blunder by picking out the strongest Forbush decreases. And by using the simple, reliable and long-provided weather-station measurements of temperature by night and day, they avoid technical, interpretive and data-availability problems that surround more direct observations of clouds and their detailed properties. The temperatures come from 184 stations scattered all across Europe (actually, so I notice, from Greenland to Siberia). A compilation by the Mount Washington Observatory that spans four decades, from 1954 to 1995, supplies the catalogue of Forbush decreases.

The prime results are seen here in Dragić et al.‘s Figure 5. The graphs show the increase in the diurnal temperature range averaged across the continent in the days following the onset of cosmic ray decreases (day 0 on the horizontal scales). The upper panel is the result for 22 Forbush events in the range 7−10%, with a peak at roughly +0.35 oC in the diurnal temperature range. The lower panel is for 13 events greater than 10%. The peak goes to +0.6 oC and the influence lasts longer. It’s very satisfactory for the Svensmark hypothesis that the effect increases like this, with greater reductions in the cosmic rays. The results become hard (impossible?) to explain by any mechanism except an influence of cosmic rays on cloud formation.

To be candid, these results are much better than I’d have expected for observations from a densely populated continent with complex weather patterns, where air pollution and effects of vegetation confuse the picture of available cloud condensation nuclei. Svensmark’s team has emphasised the observable effects over the oceans. Now the approach taken by the Belgrade team opens the door to similar investigations in other continents. Let a march around the world’s land masses begin!


USA: diurnal temperatures post-9/11

D.J. Travis, A. Carleton and R.G. Lauritsen, “Contrails reduce daily temperature range”, Nature 418, 601, 2002

Europe: diurnal temperatures after Forbush decreases

A. Dragić, I. Aničin, R. Banjanac, V. Udovičić, D. Joković´, D. Maletić and J. Puzović, “Forbush decreases – clouds relation in the neutron monitor era”, Astrophysics and Space Sciences Transactions, 7, 315–318, 2011.


23 Responses to Do clouds disappear? (4)

  1. Derek says:

    Excellent news, a way forward for the Svensmark hypothesis over land masses.

    This must really confound how the climate models “calculate” condensation rates.
    I seem to remember that NASA can not predict solar cycles too well….

    I have no doubt that this theory is part of earth’s climate system overall,
    but how big a part?
    Is it “controlling”, large, or insignificant?
    Is it a variable of just weather rather than climate?

    Also, how does the effect vary (in overall importance to the whole climate system) over time, in relation particularly to the 11 and 22 year solar cycles?


    NB – Please, Nigel, I am not political, except in the commonly left wing interpretation that “everything” is political.
    I find a lot of the people who try to demean what I try to discuss, or argue and use debating tactics against me, as usually happens elsewhere, are however.
    That does not make me political per-se I hope, more of a “target” for those that are politically motivated.

  2. matthu says:

    No comment yet from Wolfendale or Sloan?

    (I notice that the editor of ASST has not yet resigned – presumably that it because the result has stayed very much below the radar?)

  3. Bengt A says:

    Nice one!

  4. […] del blog de Nigel Calder [–>], “padrino” periodístico de Svensmark y su teoría de que los rayos cósmicos son una […]

  5. Bernd Felsche says:

    Anybody interested in finding and looking through 30+ years’ worth of global weather satellite images to reconstruct cloud cover data?

    Agricultural research stations may also have historical data on insolation near ground level onto a horizontal surface. When adjusted for solar time of day, it can provide an indication of atmospheric “transparency” during the day.

    Insolation data would be valuable for checking how sensible one’s guesses are of the effect of clouds seen in corresponding satellite images. If used for “calibration” of albedo models, they no longer provide a sensible validation of albedo as they cannot possibly falsify.

  6. dahuang says:

    Hi Nigel, as to the explanation of 911 issue, how do you think of this point of view? I am not sure whether it is for or against Svensmark hypothesis.

    “…It is shown that the increase of the average daily temperature range (DTR) over the United States during the three-day grounding period of 11–14 September 2001 cannot be attributed to the absence of contrails, a subject was debated in several previous studies. The present analysis suggests that the DTR is attributed to the change of low cloudiness. ”

    Hong, G., P. Yang, P. Minnis, Y. X. Hu, and G. North (2008), Do contrails significantly reduce daily temperature range?, Geophys. Res. Lett., 35, L23815, doi:10.1029/2008GL036108.

    • dahuang says:

      Click to access 2008GL036108.pdf

      A free copy of the Hong et al. (2008) paper.

      • calderup says:

        Thanks for that, Dahuang.
        It doesn’t really matter what the reason was, for the post-9/11 increase in DTR, as long as everyone accepts that a loss of cloud was involved.
        The lifelong journalist in me couldn’t resist the 9/11 connection, alhough being vaguely aware of latter discussions I did insert “apparently” into the contrail story.

  7. […] Nigel Calder the co-author of The Chilling Stars: A Cosmic View of Climate Change also posts on his blog Calder’s Updates. This morning ten years after the 9-11 event he reminds us of a climatic footnote to the 9-11 disastrous attack on America by islamic terrorists in his post Warmer days and cooler nights when cosmic rays are scarce […]

  8. […] 3a) News and Comments, 3c) Falsification tests. You can follow any responses to this entrance by a RSS 2.0 […]

  9. timetochooseagain says:

    Indeed the “Travis hypothesis” has been disputed by many other authors. The event in question does appear to be associated with a change in cloudiness. It just happens that this was a coincidental, natural cloud change from a particular confluence of air masses over the US:

    Click to access c026p001.pdf

    “Pictures taken shortly after the attacks show clear skies in New York, Washington, and Pennsylvania, and these transparent conditions were present across a large portion of America on 11 and 12 September 2001 (Fig. 1), while the days that followed showed increasing cloudiness. It is possible that the relatively transparent conditions for a few days after the attacks produced the observed jump in the DTR, not the lack of contrails.”

    “On 11 September, the country was experiencing unusually clear, cool, and dry conditions with dry polar air masses reported at 75% of the stations. September 12 had similar conditions, with dry polar air masses reported at 70% of the stations. September 13 was a
    day of transition across the country as the unusually clear pattern began to retreat, bringing in cloudier, more humid air. As a result, 42% of the stations reported either moist tropical, moist moderate, or moist polar air masses, while 46% of the stations reported dry polar. Concurrently, a sharp decrease in average daily temperature range was observed (Fig. 3). By September 14, much of the country was shrouded in clouds, with 44% of the stations reporting moist air masses and only 27% reporting dry polar air. This shift in air-mass pattern is illustrated in the unusually high
    average daily temperature range on September 11 and 12 with declining temperature ranges thereafter (Fig. 3).”

    “By controlling for the air masses present across the US, we found that the unusual temperatures on 11 and 12 September were a result of a particularly clear weather pattern, not a lack of jet contrails.”

    So what happened was that a particular pattern of air masses just occurred, that was associated with very little cloudiness in general. The lack of contrails was essentially coincidental.

  10. […] Nigel Calder writes: It was published on 31 August and the full text is available here  It’s typical of the pathetic state of science reporting that I still seem to have the story to myself ten days later. […]

  11. […] verkar styrka sambandet mellan kosmisk strålning och molnbildning ytterligare. Se här, här och här. Se även denna intressanta kommentar på […]

  12. […] Do clouds disappear? Warmer days and cooler nights when cosmic rays are scarce […]

  13. […] rays, wolken en temperatuur correleren op tijdschaal van luttele dagen? Ik niet want er stond niks.Nigel Calder brengt het nieuws de blogosfeer binnen en is ook verbaasd dat hij het nieuws 10 dagen voor zich […]

  14. […] Here’s another link providing some back ground […]

  15. Richard J says:


    I’ve been waiting at this bus stop for months, waiting for the ‘Whoosh- not missing just busy’ bus to arrive. Not cancelled I hope?

    • calderup says:

      Thank you for your patience, Richard.
      No cancellation, but unexpected delays for both scientific and personal reasons.
      Sooner or later the ‘bus’ will arrive, in one form or another, and I believe it’s worth the wait.
      Meanwhile I’ve tried to keep abreast of the main Svensmark-related news.

  16. Orson Olson says:


    There is an interesting discussion of clouds/albedo and their impact on climate going on over at Tallbloke’s Talkshop.

    I hope you enjoy checking it out!

  17. Kate RC says:

    Most interesting and encouraging. Thankyou.

  18. very interesting, I remember reading an article about jet contrails and how they help ‘seed’ clouds and can make it rain more then nature intended!

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