Do clouds disappear?

Falsification tests of climate theories

Do clouds disappear when cosmic rays get weaker?

or “Don’t you worry, my dear, we’ve seen no tigers”

The Sun makes fantastic natural experiments” Henrik Svensmark says, “that allow us to test our ideas about its effects on the Earth’s climate.” Most dramatic are the events called Forbush decreases. Ejections of gas from the Sun, carrying magnetic fields, can suddenly cut the influx of cosmic rays coming to the Earth from exploded stars.

According to the Svensmark hypothesis, cosmic rays seed the formation of low clouds, so there should be a reduction in the Earth’s low cloud cover in the aftermath of a Forbush decrease. During the past few years there have been repeated attempts to declare the hypothesis falsified, when various teams failed to find the expected decrease in the low cloud cover.

One morning in April 2008, I woke up to find that since midnight the BBC had spread all around the world the news that British physicists had more or less destroyed the Svensmark hypothesis. Violating a basic principle of objective reporting, the broadcasts went out before Svensmark himself had a chance to comment.

By lunchtime he and I had done our best to limit the damage – and the deception of the public – in brief radio and TV interviews. A remark from Svensmark went belatedly onto the BBC website, that the critic it quoted had “simply failed to understand how cosmic rays work on clouds”.

Two years later, critics still don’t understand it. But they go on telling the tale that Forbush decreases have no important effect on clouds, and the media go on echoing them. When Svensmark and his colleagues published in August 2009 a report that showed very clear effects, and explained why others had failed to see them, the BBC and almost everyone else ignored it. But not the scientific critics, who returned to the fray in December 2009 and February 2010.

A Scientific American headline on 9 February 2010

In my dictionary, kibosh means “kill off finally”. Svensmark commented to me, “It’s crazy. They’re making all the same mistakes that we did ten years ago, when we were first looking at the Forbush decreases.”

Scientific journals and smart journalists usually give only passing attention to negative results. Once you’ve confirmed that the Moon is not made of green cheese, that’s enough, thank you. But endless repetitions about Forbush make them the chief Popperian-style effort to falsify the Svensmark hypothesis, which is known to be the strongest challenger to the assumptions of the man-made global warming hypothesis.

2008: Sloan & Wolfendale + Kristjánsson v. Svensmark

The stir in April 2008 followed a report by Terry Sloan (Lancaster) and Arnold Wolfendale (Durham) in Environmental Research Letters. Their paper included a discussion of clouds at different latitudes, but I’ll leave that till later and focus on their main point about the Forbush decreases. They noted previous suggestions of an observable effect on clouds but concluded there was none.

Sloan & Wolfendale considered whether 24 Forbush decreases during 1984–2005 gave rise to changes in low cloud cover as recorded by the International Satellite Cloud Climatology Project (ISCCP). This project pools visible and infra-red observations of clouds by geostationary and polar-orbiting satellites. In most cases (black circles in the figure below) Sloan & Wolfendale compared the globally averaged low cloud cover in the month when the Forbush decrease occurred with the average of the three preceding months. For some large events (open squares) the timescales were shorter – clouds for one week after the event compared with those for 14 days before it.

Sloan & Wolfendale's graph (2008) of changes of low cloud cover (LCC) accompanying Forbush decreases. The expected disappearances (slope LCC CR) were certainly not evident in the data used here.

A reader unaware of the nuances of the subject might look at the Sloan & Wolfendale figure, see that on average there was no change in low cloudiness, and say, “Test failed.” Indeed, some people thought Svensmark was just being stubborn not to admit there and then that his theory was dead. Wasn’t Sir Arnold Wolfendale an ex-Astronomer Royal and the UK’s top expert on cosmic rays? Hadn’t he presided over talks at CERN in Geneva about experimental tests of the Svensmark hypothesis?

Soon afterwards, Jón Egill Kristjánsson (Oslo) reported another test of the Forbush effect. He and his colleagues used four types of cloud data from the Moderate Resolution Imaging Spectroradiometer (MODIS) microwave instrument on NASA’s Terra and Aqua satellites and looked for the impact of 22 Forbush decreases. “No statistically significant correlations,” they said, “were found between any of the four cloud parameters and [galactic cosmic rays].”

The BBC showed this graph, saying it cast “further doubt on the notion that cosmic rays are a major influence on the Earth’s climate”. With the cloud amount apparently increasing after the cosmic rays went to a minimum, a fair-minded onlooker might well say, “There you go, the Svensmark hypothesis has failed the test again.”

But back in Copenhagen, Svensmark had been re-investigating Forbush decreases for himself, together with his young colleagues Torsten Bondo and Jacob Svensmark. He not only found the impacts but knew exactly why neither Sloan & Wolfendale nor Kristjánsson & Co. could do so.

These investigators, he said, were like explorers returning from a jungle and reporting, “We saw no tigers, so there can’t be any there.” Clouds change a lot from day to day for purely meteorological reasons, whatever the cosmic rays are doing. Those variations can hide the cosmic rays’ effects as easily as undergrowth conceals the camouflaged coat of a tiger. Only by knowing how to watch for a tiger will you have much chance of spotting it before it eats you.

2009: Svensmark, Bondo & Svensmark

With the right tracking skills, the Copenhagen team confirmed all their expectations about the Forbush decreases. The first chance to try to put Sloan right came in October 2008, at a scientific conference in Oslo, where Svensmark showed some slides. But getting papers published in scientific journals has never been easy for his team, and another ten months were to pass before the Forbush paper finally appeared in Geophysical Research Letters in August 2009. It told of huge impacts of the Forbush decreases on clouds and on the aerosols that seed them.

Compare the Kristjánsson graph above with four of the Danes’ below, and you’ll see a quite different picture. The first of them shows a temporary shortage of fine aerosols, chemical specks in the air that normally grow until water vapour can condense on them, so seeding the liquid water droplets of low-level clouds. The remaining three graphs display the observable loss of the clouds that would have been seeded if the aerosols had survived to do their job. Three different kinds of satellite observations tell the same story.

First of 2 pairs

Combined data for the five strongest Forbush decreases since 1998 show a loss of fine aerosols from the atmosphere, especially about 5 days after the cosmic ray minimum (red curve). Within a few days after that, three different sets of data from satellites revealed the loss of low, wet clouds, with clouds over the oceans holding about 7 % less liquid water than they did before the events. Dates of the five Forbush minima, ranked in order of the downturn in ionization of the lower air, compared with the overall variation in the course of a solar cycle, were 31/10/2003 (119 %), 19/1/2005 (83 %), 13/9/2005 (75 %), 16/7/2000 (70 %) and 12/4/2001 (64 %).

In preparing for this successful hunt, the team’s first task had been to calculate the effects of many solar outbursts on the Earth’s space environment. They were then able to identify and put in rank order 26 Forbush events since 1987 that caused the largest reductions in the energetic cosmic rays that affect the air at low altitudes. The results of laboratory experiments by Svensmark’s team already gave them a clear idea of what the observable chain of events in the atmosphere should be, following those Forbush decreases.

Cosmic rays continuously promote the formation of micro-clusters of sulphuric acid and water molecules, but initially these are far too small to be detectable by remote observation. After growing routinely over a number of days the invisible specks floating in the air influence the normal colour of sunlight as seen from the ground, by scattering away its violet light. Conversely, a shortage of fine aerosols after a shortage of cosmic rays should make the Sun appear abnormally bright in at the violet end of the spectrum.

AERONET (AErosol RObotic NETwork) is a federation of networks led by NASA and CNRS. Here the solar monitor is on the right. NASA photo.

Ground-based stations of the world-wide AERONET programme monitor subtle changes in the colour of sunlight and, bingo, the Sun’s violet light intensified after the strongest Forbush events. Interpreted as a loss of fine aerosols, these fell to a minimum about five days after the lowest counts of cosmic rays.

Next, the impact of the Forbush decreases on clouds should become apparent. To trace them, the three sources of data used by Svensmark, Bondo and Svensmark were independent of one another. First, the Special Sensor Microwave/Imager (SSM/I) instruments of the US Defense Meteorological Satellite Program cover the world every three days, measuring the liquid water content of clouds over the oceans.

Defense Meteorological Satellite Program (DMSP) Image: USAF Research Laboratory

From the MODIS data (also used by Kristjánsson) the Copenhagen team took the liquid water cloud fraction (LWCF). Thirdly, the ISCCP data were of the same kind as those used by Sloan & Wolfendale, namely low clouds over the oceans detected by infra-red.

As the graphs above show, all of these observational data sets showed much the same pattern of events after the strongest Forbush decreases since 1998, namely a decrease in liquid water clouds that reached its lowest point six to nine days after the mimimum count of cosmic rays.

This was longer than some other experts expected. For example Sloan & Wolfendale stopped looking for any effect seven days after their largest events (less, really, because they started their count sooner). But knowing the wide range of opinions among aerosol chemists about the rate of growth of cloud condensation nuclei, Svensmark himself was not surprised by the result – just glad to be able to give those experts useful information about how small aerosols behave in the Earth’s atmosphere.

As for the magnitude of the impact on cloud cover, it was huge. A 7 % decrease in cloud water seen by SSM/I translates into 3 billion tonnes of liquid water vanishing from the sky. The water remains there in vapour form, but unlike cloud droplets it does not block sunlight trying to warm the ocean. After the same five Forbush decreases, the extent of liquid-water clouds measured by MODIS fell on average by 4 %, while ISCCP showed 5 % less cloud below 3200 metres over the ocean.

The four observational data series start from different years, and the wish to compare the aerosols and clouds fixed the time-frame for the results shown already, because AERONET was the Johnny-come-lately. But as the team had identified 26 strong events going back to 1987, they were able to plot their impacts throughout the life-span of each set of observations, as compared with the relative strength of each event.

When the observed impacts of relatively weak decreases in cosmic rays are included, the blue trend lines show, as expected, a decreasing effect, so the impacts begin to hide in the meteorological “noise”. The thin black lines above and below each point denote the uncertainty in the data.

The blue lines are statistical fits to all of the plotted data points. In all four cases the the impact increases as the decrease in cosmic rays gets bigger, so for the Svensmark hypothesis, test passed.

These graphs also show why other trackers failed to spot the tigers. Sloan and Wolfendale used the ISCCP data, for which the uncertainties (black error bars in the graphs) are particularly large. What’s more, most of their data points relate to monthly averages of cloudiness (ISCCP D2), which means that any Forbush effect lasting a week or so is likely to be smothered by three other weeks of quasi-random and unrelated changes in cloudiness.

For MODIS the error bars are smaller, but while Svensmark, Bondo and Svensmark selected only 13 Forbush events in the period 2000–2007, Kristjánsson et al. used about 22. “As a result,” the Danes concluded, “their data were dominated by weak events that would be plotted to the left of our data … in a region where uncertainties due to variations in meteorology are much greater than the [Forbush decrease] signal.”

From solar activity to cosmic ray ionization to aerosols and liquid-water clouds, a causal chain appears to operate on a global scale. Those were the closing words of the report by Svensmark, Bondo & Svensmark in Geophysical Research Letters. Confident that his hypothesis had survived this important falsification test, Henrik Svensmark hoped that any open-minded physicist should be quite impressed by the results.

2009-2010: the fight goes on

Open-mindedness is often in short supply in climate physics and Svensmark trod, not for the first time, on the toes of the supporters of the man-made global warming hypothesis. A loss of 4 or 5 % of low clouds may not sound very much, but strong Forbush decreases briefly boost the sunlight reaching the oceans by about 2 watts per square metre – equivalent to all the global warming during the 20th Century.

Although they are too short-lived to have a lasting effect on the climate, the Forbush decreases dramatize the cosmic climate mechanism that works more patiently during the 11-year solar cycle. When the Sun becomes more active, the decline in low-altitude cosmic radiation is greater than that seen in most Forbush events, and the loss of low cloud cover persists for long enough to warm the world. That explains the alternations of warming and cooling seen in the lower atmosphere and in the oceans during solar cycles. And the overall increase in solar activity during the 20th Century implies a loss of low clouds sufficient to explain most of the “global warming”.

So the critics have been keen to continue the battle and to say that Svensmark, Bondo and Svensmark’s Forbush results must be wrong. First back in the fray, in December 2009, was Arnold Wolfendale, this time in association with geographers at Sussex, Benjamin Laken (lead author) and Dominic Kniveton. For some reason they concentrated their attention on just one of the four data sets used by the Danes, the MODIS low cloud fraction LCF. These were their main complaints.

  • They thought the timescale concerning aerosol growth into cloud-condensation nuclei was unbelievable. Amazingly, Laken, Wolfendale and Kniveton relied on the say-so of a particle physicist at CERN, that it would be two days at the most, compared with the six to nine days observed. This is a subject on which Svensmark and his colleague Martin Enghoff have published a lengthy scientific review and they know there is a much wider range of opinion among experts about aerosol growth rates than Wolfendale’s hit-men imagine.
  • The five strongest events used by Svensmark and Co. were said to be “incoherent”, with only the second strongest showing the effect claimed, and that for extraneous reasons. Surprisingly neither the journal’s editors nor their referees asked for any statistical warranty for these arm-waving statements.Incoherent? Judge for yourself.

I happen to have to hand four of the five individual events used by the Danish team before conflation. They show cloud water, not low cloud fraction, but they are good examples of what the individual events look like.

Red curves are cosmic rays, the black, cloud water, the blue, cloud water over 2 days. The stars and bars show the natural variability in cloud water.

All are untidier than the conflated graphs, where random-looking meteorological “noise” tends to cancel out. Is there anything particularly odd about that second strongest event (second from the left above) as Laken, Wolfendale and Kniveton suggested? Well, there was a previous dip in cloud water unrelated to the cosmic ray changes, but so there was in other cases illustrated. In every case shown, the cloud water (blue) was lower than usual 5-10 days after the cosmic ray minimum (red).

Another falsification attempt came In February 2010.Sudden cosmic ray decreases: No change of global cloud cover” is its title, once again in Geophysical Research Letters. The lead author is Jasa Calogovic of the Hvar Observatory in Croatia, but it is the work of a Swiss-German collaboration of scientists from the University of Bern and EWAG led by Frank Arnold from the Max Planck Institute for Nuclear Physics in Heidelberg. It inspired the “Forbush Puts Kibosh on Theory” headline quoted near the outset.

At the risk of discourtesy to the distinguished authors, I can report that Svensmark laughed when he read the paper from Arnold’s group. Where his own team studied three different satellite data sets and 26 Forbush decreases, Arnold’s took just one data set (ISCCP) and only six events – those ranking 4th, 10th to 13th, and 26th, in Svensmark, Bondo and Svensmark’s assessment of effects on cosmic rays reaching the lower atmosphere. In the Danes’ plot of all their ISCCP results (see above) all but one of the Swiss-German selection have “strengths” between 33 % and 69 %, where any reduction in clouds is similar to the uncertainty. “Of course they couldn’t see anything,” Svensmark said to me.

Bringing the Earth’s magnetism into the story

Both Wolfendale’s and Arnold’s teams repeated a different complaint going back to Sloan and Wolfendale in 2008, about clouds at different latitudes. In promising to return to it later, I was saving the neatest rebuttal till last. Here, for example, is how Laken, Wolfendale and Kniveton expressed their concern.

An analysis of the latitudinal distribution of the [low cloud fraction] variations reveals that this decrease is predominately located at mid to low latitudes, whereas if the phenomenon were related to variations in the [cosmic ray] flux it should be predominately located at high latitudes.”

What this is all about is the influence of the Earth’s magnetic field on the influx of cosmic rays. As a shield of sorts, it works much better in the tropics than towards the magnetic poles. So with more cosmic rays coming in at higher latitudes, and varying more, shouldn’t there be a bigger effect on clouds there, than at at low latitudes?

The argument was most clearly illustrated by Sloan & Wolfendale, with a diagram that related not to sudden Forbush decreases but to long-term variations in cosmic rays over Solar Cycle 22 (1983-96) and to an earlier report on their effects on clouds by Nigel Marsh and Henrik Svensmark in 2000. I’ve replaced rather technical labels on the axes of the graph with simpler ones of my own.

From Sloan & Wolfendale 2008 with axis labels simplified.

The line NM is the variation in cosmic rays at different latitudes, which Sloan & Wolfendale say should be followed by any variation in low cloud cover if the Svensmark effect is real. The various symbols show the actual variations in the clouds according to an analysis of ISCCP data, which are obviously missing the target line completely.

Test failed? Not a bit of it. Here is the same graph with a red line added by Svensmark, showing how he computes that the cloud effect should vary with latitude. It fits the Sloan & Wolfendale data surprisingly well, when you remember how “noisy” the ISCCP data are.

A neat rebuttal from Svensmark, personal communication 2008. The added small diamonds linked by the red line are computations of relative changes in lower air ionization at various latitudes.

Test passed. We have come to the nub of the misconception, where the critics haven’t grasped an elementary point about Svensmark’s physics. For ten years he has said the clouds most affected by cosmic rays are low clouds. So the cosmic rays that matter are charged particles (mainly muons, heavy electrons) that penetrate low into the atmosphere. They’re generated mostly by very energetic protons from the Galaxy on which the Earth’s magnetic field has little influence. Hence the much reduced slope of the red curve, compared with Sloan & Wolfendale’s NM slope.

NM stands for neutron monitors, and there’s the blunder. Neutrons are very handy for showing changes in cosmic ray intensities, whether in a Forbush decrease or during a solar cycle. But as high-school students know, neutrons are uncharged. They don’t ionize the air or affect the clouds. To rely on neutrons to tell you what the clouds should do is as rash as expecting tigers to have smoke coming out of their heads.

The overriding importance of the muons is the reason why Svensmark’s team went to so much trouble to compute the ionization of the lower air for many Forbush decreases. None of the critics cited here used the same reckoning to lead them to the effects on clouds. This is what lay behind Svensmark’s remark to the BBC back in 2008, that Sloan “simply failed to understand how cosmic rays work on clouds”.


That said, it’s hard to avoid the impression that Svensmark’s critics don’t want to understand the physics, or to see the Forbush effects on clouds, because Mother Nature is not being politically correct. When the Sloan & Wolfendale report came out in 2008, the Institute of Physics in London put out a press release saying it refuted a TV programme, The Great Global Warming Swindle (which briefly mentioned the Svensmark hypothesis). In a press release from Lancaster University, Sloan said that seeing that documentary provoked his research, although he claimed he was “open-minded” about what he’d find. As for Wolfendale, he has criticized the editor of Astronomy & Geophysics for daring to publish an article by Svensmark in 2007.

And these two go on nagging at the issue, most recently in the CERN Courier in February 2010. In company with Anatoly Erlykin of Moscow’s Lebedev Physical Institute, they introduce a new argument, about an apparent decline in low clouds in recent years. (That will be the subject of a later “Falsification” note.) The authors also make rather rambling excursions through the possible roles of cosmic rays in lightning and the origin of life on Earth – perhaps in case the reiteration yet again of their shaky argument about geomagnetic latitudes might set their readers yawning.

Don’t you worry, my dear, we’ve seen no tigers.” With reassurances from big-cat experts like these, would you leave your gun at home when going into the jungle? Or stake the well-being of the Earth’s people, who have to cope with the ever-changing climate, on the belief that the Sun’s variations, amplified by the cosmic rays, don’t matter any more?

A last word from Svensmark, in a comment to a Swiss journalist when the report by Arnold’s group came out in February 2010: “The case for cosmic rays and their impact on clouds looks better than ever.


T. Sloan and A.W. Wolfendale, Environ. Res. Lett., 3, 024001, 2008

J. E. Kristjánsson et al. Atmos. Chem. Phys., 8, 7373–7387, 2008

H. Svensmark, T. Bondo and J. Svensmark, Geophys. Res. Lett., Vol. 36, L15101, 2009

Laken, B., A. Wolfendale, and D. Kniveton (2009), Geophys. Res. Lett., 36, L23803, 2009

M.A.B. Enghoff and H. Svensmark, Atmos. Chem. Phys., 8, 4911-4923, 2008

J. Calogovic et al. Geophys. Res. Lett., 37, L03802, 2010

N. Marsh and H. Svensmark, Phys. Rev. Lett., 85, 5004, 2000

A. Erlykin, T. Sloan, A. Wolfendale, CERN Courier, 24 February 2010

BBC reports April 2008 and

DTU press release on the Svensmark, Bondo & Svensmark paper 2009

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35 Responses to Do clouds disappear?

  1. Derek says:

    My apologies if there is an appropriate open thread / post to put such comments in, I have missed it so far.
    Please excuse me, however, I would like to post the following.

    I have just discovered you are now blogging by accident.
    Just yesterday I was watching again the swindle documentary by Paul Durkin (that changed so many people’s views, and lives) and thinking ALL the main points were already covered and “known” how many years ago..
    Your comment in the documentary about researching squirrels with climate change added to the funding reguest will go down in the annuls of the AGW scam.

    It is great to discover such a big name is now blogging.
    Thank you.


    • calderup says:

      That’s fine, Derek — you’ve commented in the right place, and thanks for your interest.
      By the way, the Swindle producer is Martin Durkin.

  2. Derek says:

    Oooops Martin Durkin, of course, my apologies.

    I took a lot of flack at the CPDN forum trying to discuss the documentaries points at the time – but that’s no surprise it is a climate modelling forum..
    That lead me to where I am now at “home” GWS forum, and a thread there I started because of this blog.
    You may find it interesting / relevant.

    • calderup says:

      Derek, I’m more interested in the physics than the politics, but since you raise the matter of the documentaries — Inconvenient Truth and Swindle I presume — I’m wondering whether to create a new Category for that kind of stuff. Meanwhile here are remarks about those documentaries in a talk I gave in London 18 months ago.

      Excerpts from a talk by Nigel Calder at the Savile Club, London, 2008.

      I must admit, poor little drowning bear cubs make dazzling propaganda, of a kind to which schoolchildren in particular are vulnerable. In that connection an English high court ruled that Al Gore’s sob story about the polar bears, in his movie An Inconvenient Truth, was groundless. It was one of nine misleading claims that the judge said must be pointed out to all teachers showing that film in school. Yet people still wring their hands about the polar bears, don’t they?
      [and later]
      Channel 4 … broadcast a film with the scandalizing title The Great Global Warming Swindle. Dozens of global warming scientists promptly weighed in with detailed complaints to the regulator Ofcom, running to about 200 pages. All they could extract from Ofcom were minor rebukes to Channel 4 about unfair treatment of three of the complainants. On a personal point, Ofcom rejected a claim by the Intergovernmental Panel on Climate Change (no less) that Nigel Calder had told lies in the Swindle film.
      Remember I mentioned the high court judge who identified nine misleading claims in Al Gore’s movie? Well, after a year of forensic scrutiny, Ofcom concluded that the Swindle film did not seriously mislead viewers, and affirmed that such challenging programmes should indeed be made.
      It’s notable that when lawyers look coolly at the evidence, they can be more objective than some people who call themselves scientists.

  3. Richard111 says:

    Hi, I was directed here by Derek. Lots of interesting stuff for me to read here. I have An Appeal to Reason, The Chilling Stars and Magic Universe, so I am already a fan. :)

    One small niggle, you seem to have a “Snapshot” thingy that I don’t get on other blogs. It does distract.

    Off to read more posts. Thanks for you efforts.
    Oh, What is “Theme Contempt”? Bottom of page, and a smiley.

    • calderup says:

      Richard, when you query ‘a “Snapshot” thingy that I don’t get on other blogs’, .do you mean the little mugshot by my name at the start of most items?
      I’m not alone in this and I took the idea from Lubos Motl of The Reference Frame.
      3 reasons for it:
      1 It’s more “open” than the geometric patterns or other symbols used as trademarks by bloggers and comment-makers.
      2 Professional writers like me formally assert “the moral right of the author” at the beginning of any book these days, and while I don’t want to copyright the posts and prevent others from quoting them, I do want to make it very clear that I wrote them.
      3. I expect to welcome other contributors from time to time and will include their mugshots too.

      There’s nothing sinister about Theme Contempt. It’s just the name of one of many themes (or top banners) offered by my WordPress hosts.

      Thanks for your interest


  4. John R T says:

    Nigel says, ¨It´s notable that when lawyers look coolly at the evidence, thay can be more objective than some people who call themselves scientists.¨
    Thank you, from the Commonwealth of Virginia, whose Attorney General wishes information on the work of a climate scientist.

  5. Richard111 says:

    No, not your picture. When my mouse pointer moves over any item on your web page with a link to another page I get a “Snapshot Preview” of that page. This triggers an “out of memory Line 1″ warning on my computer and everything stops for a while.

    I can switch the preview off and reload the page but that only works for that session. I will discuss this with my local PC Fixit expert and see if I can disable the feature on my computer. There are other sites with this feature but I keep clear of them.

    Now I must research this problem.


  6. Nigel, hi. :-) I found and rented the DVD of “The Great Global Warming Swindle”, saw it only yesterday. Just was looking through my local Blockbuster and there it was. I like to hear all sides of any argument so rented it. I live in Melbourne Australia. It all made so much sense and it’s hard to comprehend that the plain hard facts have been so distorted for vested interests. I now understand the issue.
    I felt so strongly about wanting to spread the word of the film and its message that I even came to WordPress and created a one page blog outlining (as best I could, I’m not a scientist) the error and facts behind it and a little of the political/social history to explain why people are screaming falsehoods to everyone, and having just tagged the page and published it, I clicked one of my tags and found you here through the tags list! At the time I was viewing the movie I was listening to you and wondering if one day I would ever get to find you on social media, I thought you were wonderful. And by some serendipidous turn of events I find myself right at your blog with no effort of searching. How fantastic is this informaiton age.
    Good work Nigel, I loved the film and hope the whole world gets to see it and hear it’s message. Looking after the environment is a good thing which nobody can really argue against, but being lied to about CO2 and global warming I will just not accept. Ever. Cheers.

  7. By the way Nigel, I saw the part in the film which mentioned that most warming is closer to the Earths surface than would be expected for greenhouse gasses causing it, and it was stated in the film (not by yourself) that it was a real ‘head-scratcher’. Or something like that anyway. I would suggest (my own personal view as a non-scientist) that IF humans WERE to be contributing to warming of the planet, and that warming was occurring closer to the surface than expected, if all that was being caused by humans, the cause would likely be retained heat from concrete and bricks and removal of vegetation over huge areas worldwide. Both of these things would cause the surface to get hotter. I know from living in a large city but on the green edge of it, that in the built up areas closer to the city centre it is always hotter longer from the heat retained in the roads and buildings than it is further out where I live where there are more trees everywhere and it’s greener. The more concrete and brick and road and buildings butted-up to the curb, the hotter is is by a few degrees all day. Cities and spreading urban development globally will be the likely cause of a hotter planet and also bare earth caused by huge areas of forests being daily removed in places like Brazil etc (several football fields per day for palm oil plantations etc), plus vegetated areas generally for development and farming and building. But I think mostly the concrete and buildings taking over and just retaining daily heat over extended periods of time like open-air ovens. After a hot day do what I do; hold your hand close to the road or a brick wall and feel the radiated heat coming from it. This is after the sun has gone down and the air is cool. I think if anyone wanted to blame a human activity for global temperature changes, it would be at buildings and concrete and hard surfaces. Not carbon emissions. But there’s no money or sense in ripping out roads.

  8. Danica Barff says:

    Awesome images! I appreciate the post so much! ;)

  9. Arijigoku says:

    It’s great to read your blog. The amount of detail given in this article in particular, puts the likes of the BBC to shame. It is sad that Svensmark’s critics are politically motivated but in the end the theory will be stronger for having passed their tests. Keep on going everyone.

  10. Bengt A says:

    Thank you so much for this update on cosmic rays. Really appreciate your comment on Calogovic, a paper I couldn’t get a grip on!

    One common argument against Svensmarks hypothesis is that there seems to be almost no trend in solar activity during the 20th century. Every time you are in a discussion and you mention the importance of solar activity and comsmic rays the AGW proponents go ‘no trend, no trend!’

    Are they right? Would be great with a blog post on this issue!

    • calderup says:

      Bengt, I think you must mean the “no trend since the 1980s” argument from Lockwood and others. It’s what I call “recently lazy Sun” story, already advertised as one of the topics I’ll be dealing with under Falsification Tests. Not sure when I’ll post it. But in brief, with a lazy Sun you expect global warming to stop, and that’s exactly what’s happened.

      Thanks for your interest.

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  12. Terry Sloan says:

    Sorry I have only just seen this piece.
    Henrik Svensmark is wrong to assume that most of the ionization at cloud forming height is caused by cosmic ray muons. There is a significant contribution from the so called soft component of cosmic rays. The ionization from muons and the soft component then produces a latitude dependence of the ionization which follows roughly the shape of the neutron monitor (NM) data. In our paper only the shape of the distribution was used (not the absolute level) to show that the distribution was mainly flat with less than 23% attributable to a shape like the NM data. Hence less than 23% of the dip in the globally averaged low cloud cover, reported in the original Marsh and Svensmark paper, could be caused by cosmic ray ionization. This is now borne out by the following solar cycle (peaking in 2000) where there is little sign of a dip in the cloud cover. If changes in cosmic rays cause significant changes in cloud cover we should have seen a dip in 2000 similar to the one seen in 1990 (see ).
    There is another argument which shows that it is inconsistent to postulate that most of the ionization comes from muons and at the same time that these cause the dip in cloud cover seen in 1990. It goes like this.
    Let us suppose that Henrik is correct and the change in cloud cover seen in 1990 is caused by the solar modulation of ionization from muons. This has been measured to be 2-3% (Ahluwalia, JGR 102 (1997) 24229). The dip in cloud cover at the 1990 solar maximum shown in the Marsh and Svensmark paper represents a fractional change in cloud cover of 4.5%. For a 2-3% change in ionization from muons to produce a 4.5% change in cloud requires that the change in cloud cover varies roughly as the square of the change in ionization rate. Theories of this process would predict that such a variation would be more like a square root behaviour rather than a square. Hence it is inconsistent to postulate
    that changes in ionization from muons alone cause the change in cloud cover seen in 1990.
    None of this says that there is no effect of cosmic rays on clouds. However, such an effect can only be a minor one.

    • calderup says:

      Thanks for your comment, Terry.

      1) Concerning muons versus the soft component, most of the low clouds that matter in the Svensmark hypothesis are oceanic clouds ~1 km above sea level. There, most of the ionization is indeed caused by cosmic ray muons. The CRC Handbook of Chemistry & Physics tells me that at sea level the soft component contributes about one third of the ionization and at low altitudes scarcely more. In the same elementary reference book I see that at sea-level the flux (hard and soft) increases by about 7.5% from the Equator to ~latitude 40 and then flattens out. This is very like the observed variations of low clouds in your NM plot. So the neutron monitors featured in that plot are an extremely poor guide either to the magnitude or the the shape of latitudinal variation in low-altitude ionization. The main reason for the muted latitudinal effect is that nearly all low-altitude muons are created by primary cosmic rays so energetic that the geomagnetic field has no effect on them. See Fig. 6 on page 60 of The Chilling Stars. If you want to check this, the CORSIKA program of the Karlsruhe Institut für Kernphysik is available at — but be warned, doing this physics is time-consuming. By the way CORSIKA takes full account of the soft component as well as the muons.

      2) Concerning cloud behaviour in “the following solar cycle” (i.e. Cycle 23 peaking ~2000) the ISCCP D2 IR low cloud data that you cite have well-known problems arising from the changing population of weather satellites and changes in viewing angle that affect the low cloud assessments. See for example Amato T. Evan, Andrew K. Heidinger and Daniel J. Vimont, “Arguments against a physical long-term trend in global ISCCP cloud amounts”, Geophysical Research Letters, Vol. 34, L04701, 2007. When those problems have been sorted out, I expect that the downward trend in low cloud cover will disappear and the de-trending will also reveal a variation in low cloud cover in Cycle 23 very similar to that in Cycle 22. We’ll see, when the physics is done.

      3) On your last point, about proportionality, the Ahluwalia data show a 4% fall in the muon count at the time you mention, not 2-3% as you suggest. See Fig. 2 in Svensmark, Physical Review Letters, Vol. 80, pp 5027-30, 1998. The effect on clouds may indeed be proportional to the square root of the ionization density, but if I write Δ(LCC)=k.Δ√(muon change), a 4% muon change could give a 4.5% change in LCC if k=2.25. The existence of a constant k would be unsurprising in view of the complex atmospheric chemistry involved in translating ionization into cloud condensation nuclei. But in any case, uncertainties about the ISCCP data, mentioned in (2), and questions, for example, about the atmospheric distribution of sulphuric acid molecules, mean that it would be rash to try to establish a power law from a single pair of data.

  13. Terry Sloan says:

    Several points.
    The soft component is generated by pi-zero decay and is the same over both land and sea.

    I have been studying the simulations and data and the latidude dependence of the solar modulation of cosmic ray ionization resembles that of neutron monitors. The modern simulations give a bigger soft component than is given in the CRC handbook.
    (I will send you a plot – I do not know how to put it on here).

    Concerning solar cycle 23 – if you use the data through until 2009 you can see that there is little sign of a dip. Henrik’s detrending only used data just beyond 2000 and this made it look like a dip. Have a look at the link to the ISCCP web site – the plots are there. There is not much sign of s dip in solar cycle 23. However, we will see when they have recalibrated.

    The Ahluwalia paper gives 3.6% as the fall in the muon rate in
    solar cycle 22. This looks anomalously large compared to other solar cycles so is probably a statistical fluctuation. Howver, let us take this value. Calculus shows us that if a change of 4.5% in cloud cover comes from a change of 3.6% in ionization one needs cloud cover to vary as the power 4.5/3.6=1.25 whereas simple square root behaviour would would require a value 0.5 here. Your constant k does not enter since we are discussing fractional changes i.e. relating Delta(LCC)/LCC and Delta(Ionization)/Ionization (i.e. assuming LCC=k Ion^power).

  14. Max_B says:

    The following paper was published last year in GRL, and has concerned me for some time. Does it not have some impact in this debate? Not just on Svensmark’s muons, but also on historical measurements of Be-10 & C-14…?
    i.e. Does a warmer less dense atmosphere leads to less GCR strikes making less Be-10 & C-14. Whereas a colder denser atmosphere leads to more GCR strikes making Be-10 & C-14. This seems important, as a link between these light radio-isotopes and paleoclimatic temp reconstructions has been made by Svensmark:
    “Sudden stratospheric warmings seen in MINOS deep underground muon data” Osprey, S.M. et al.,
    here’s a link to the press release:

    Here are three important parts of the press release:

    “What they observed was a strikingly close relationship between the cosmic-rays and stratospheric temperature – this they could understand: the cosmic-rays, known as muons are produced following the decay of other cosmic rays, known as mesons. Increasing the temperature of the atmosphere expands the atmosphere so that fewer mesons are destroyed on impact with air, leaving more to decay naturally to muons. Consequently, if temperature increases so does the number of muons detected.”

    “What did surprise the scientists, however, were the intermittent and sudden increases observed in the levels of muons during the winter months. These jumps in the data occurred over just a few days. On investigation, they found these changes coincided with very sudden increases in the temperature of the stratosphere (by up to 40 oC in places!).”

    “Now we can potentially use records of cosmic-ray data dating back 50 years to give us a pretty accurate idea of what was happening to the temperature in the stratosphere over this time. Looking forward, data being collected by other large underground detectors around the world, can also be used to study this phenomenon.”

    I’m no scientist, but I do follow Svensmarks hypothesis closely, and would welcome any comments as to this paper’s possible impact on it.

  15. Douglas McCormack says:

    Hi, Is there any news of the initial results from the Cloud 9 experiment at CERN? If I remember rightly, Jasper Kirkby anticipated results very early on in the project and proposed publishing their provisional findings by mid-year 2010 – I’ve heard nothing from the CERN site!

  16. Jeff (of Colorado) says:

    Perhaps I need to buy a copy of The Chilling Stars to answer this question, would the Cosmic Rays of a Super Nova be the right kind of rays to cause the oceanic clouds you have mentioned? More specifically, whenever Betelgeuse explodes, could it cause those clouds? Given the delay between light and cosmic rays from an exploding star, what is the delay in arrival and subsequent time period of increased cosmic rays?

    While Betelgeuse may not explode for many tens of thousands of years, an
    explosion soon and any subsequent cooling would hit during what is looking like Solar Minimum. What a Pyrrhic victory for your theory, sort of……..

    • calderup says:

      So, Jeff, what will happen when Betelgeuse blows up as a supernova? Nothing sudden or dramatic, I’m glad to say, for the sake of the people who suffer when the clinate cools.
      You’ll find no direct answer to your question in The Chilling Stars, but a useful starting point is the event about 2.8 million years ago, described in Chapter 7, “Children of the supernovae”. (There was some subsequent dithering about the date but the team involved reverted to 2,8 million years, as note in the Postscript to the 2008 edition.)
      A supernova exploded close enough to strew the Earth with detectable quantities of a radioactive form of iron, iron-60, made by the dying star. According to the researchers at the Technological University of Munich who found the surviving iron-60 atoms atoms in ferromanganese deposits from the Pacific Ocean floor, the supernova must have been no more than about 100 light-years away from the Solar System.
      Generating the cosmic rays takes time. The accelerators in a supernova remnant produce them for a few hundred thousand years. That’s why the Munich team linked their supernova to iciing in the North Atlantic 2.75 million years ago and the replacement of African forests by the grassland that played a key role in human evolution.
      The massive red giant star Betelgeuse, in Orion’s shoulder, is due to go supernova ‘some time soon’, which in astronomical terms could mean today or in 100,000 years’ time. The closest estimate of the distance to Betelgeuse (from ESA’s Hipparcos astrometric satellite) is 427 light-years (or 131 parsecs). That is much farther than the 2.8 million-year event although still among the close supernovae expected to produce spikes in the cosmic-ray count. On the other hand, while new supernovae like Betelgeuse may come ‘on stream’, the cosmic rays from other events of the past half-million years are fading.
      So don’t expect any sudden or dramatic effect, Jeff, from Betelgeuse that could settle the climate argument. The quiet Sun will probably be of more hel in that regard.
      There is a related post at

      • Jeff (of Colorado) says:

        Thank you for the explanation and the link! Most informative!

  17. aaron says:

    Another missed factor is that aerosol concentrations are already high near land. Areas with high average concentrations should be avoided to see the effect. This will leave areas over the oceans, where the effect would be most aparent. Not only will the effect be greatest there, the effect on temperature is greatest too, since albedo is low absent clouds.

  18. [...] vor.….2011.504.html…uds-disappear/ Deutsch liest man sowas nur in nicht-mainstream Blogs: [...]

  19. [...] From Nigel Calder: 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 link [...]

  20. James Kress says:

    Another effect of ionizing radiation, not mentioned here, is the impact it has on IR absorption by the species that dominate the AGW discussion. They will be ionized by the radiation and their IR absorption spectra will change. I’ve done detailed, high level TDDFT calculations and been able to show that the IR spectra of the ionized species shift so that their absorption of IR radiation is minimized or eliminated.

    • calderup says:

      Not sure that’s very effective, James. The ionization of greenhouse molecules will be relatively rare and short-lived, won’t it?

  21. Andrew McRae says:

    “…If we compare the times of these transits with changes in the climate of Earth, the claimed correlations not only disappear, but we also find that they cannot be resurrected for any reasonable pattern speed.”

    Will be interesting to see who responds to that paper.

  22. Andrew McRae says:

    In the infamous Wikipedia, Pierce2009 is referred to as evidence that cosmic rays cannot create large enough particles to affect cloud forcing. In usual warmist deception style, when you actually check what that paper studied it turns out the paper was a model *simulation* result, not an actual observation.

    These days Pierce seems quite happy to admit the science isn’t settled and that CLOUD could lead to his models being changed.

    I have to say after looking at the data that there is no evidence that GCR flux modulation has led to any warming in the 20th century at all, indeed the trend for all the neutron count data we have available since 1957 goes in exactly the opposite direction than would be predicted. There is a very slight upwards trend, which should have led to a bit of cooling, not warming. The GCR humps don’t always line up with temperature swings either. Presumably the amount of GCR change over the last two decades is small compared to the flux change over the last thousand years, but I can’t find any data about that.

  23. Max_b says:

    Svensmark apparently gets a pretty good fit over the last 20 odd years when he plots Huancayo/Haleakala Neutron data (as a proxy for muon’s), against tropospheric air temperature (HadAT2), or ocean sub-surface water temperature (SODA).

  24. [...] až devět dnů. Ale Sloanův tým přestal hledat po sedmi dnech. Sloanovy argumenty podrobně vyvracel na svém blogu Svensmarkův spolupracovník Nigel [...]

  25. [...] Blandar man molndata från en hel månad eller två så försvinner denna nedåtpeak av molnmängden i det statistiska bruset. Hela historien finns här. [...]

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