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Revisiting Svensmark & Friis-Christensen (1997)

Posted by Ari Jokimäki on February 15, 2010

Lately I have been putting together stuff with intention to write a thorough review of the situation with the role of the cosmic rays in the climate. For that, I read for the first time the original Svensmark & Friis-Christensen (1997, “SF97” from hereafter). To my surprise, I found out that their whole thing seems to be based on false cloud trends. Some of you might have read my previous writing of ISCCP problems. It turns out that SF97 use ISCCP data to show a correlation between clouds and cosmic rays.

At one point, they say this about cloud cover:

“In Fig. 2 it is seen that a pronounced variation (corresponding to 3%-4%) takes place during this period with a maximum around 1986-1987, close to the minimum in solar activity.”

Their Figure 2 then shows that situation with the changes in cosmic rays and there indeed seems to be good correlation between the two in the short interval they are presenting. Both increase roughly from 1984 to 1987 and then decrease from 1987 to 1990.

Among others, Evan et al. (2007) have studied the problems in ISCCP cloud data. They noted that addition of satellites to the measurement network causes decrease in the measured cloud cover due to the changes in the satellite viewing angle. They listed some points in time when there had been remarkable changes in the satellite network. One of the changes is the launch of satellite GOES 7. It happened in February 1987 and fits well to the strong decrease in the ISCCP cloud data at that time. Evan et al. also showed how the trends change if one uses only the regions where viewing angle problem does not affect the data much. They presented it in their Figure 3. Figure 1 here shows the Fig. 2 of SF97 and Fig. 3 of Evan et al. Note that the cloud cover changes are little different in these two because SF97 only used data taken over oceans.

Figure 1. Figure 2 from SF97 (top panel) and Figure 3 from Evan et al. (bottom panel). The data from regions affected less by the viewing angle problem has been highlighted with red between the time period with ISCCP data (about 1984-1990) used in SF97.

When we look at the data highlighted with red that presents the time period where SF97 showed the correlation (shown in top panel of Figure 1 above), we notice that the cloud trends between that time have disappeared almost completely. What follows is that the correlation presented in SF97 is most likely not real but a result of ISCCP viewing angle problem.

After this, SF97 show the situation with other cloud data in their Figure 4, but that image is very unclear. It is difficult to estimate if the other cloud data supports the correlation or not. I first thought that this was just due to scanning the original paper to electronic format, but Laut (2003) has also noted the blurred appearance of the figure, so the problem was already in the original publication. However, it can be seen from Laut’s discussion that the other cloud data don’t support the correlation (putting the blurred appearance of SF97 figure and its presentation as if it would support the correlation in not so pleasing light), so the correlation presented in SF97 seems to rest on the ISCCP data alone.

SF97 also show that the correlation is less near the equator and they think it supports their view. If the apparent correlation would be due to ISCCP viewing angle problem, then the geometry of the problem would also cause the correlation to appear less near the equator because at the equator there is generally less affected areas than elsewhere.

So, there you have it. It seems in a strange way quite amusing to think that the whole of this cosmic ray issue might have been resting on the ISCCP viewing angle problem in the original paper and the later works have just been stamp collecting the apparent correlations here and there. In this light it is not surprising that we keep finding lot of problems with the cosmic ray hypothesis.


Evan et al. (2007), “Arguments against a physical long-term trend in global ISCCP cloud amounts”, Geophys. Res. Lett., 34, L04701, doi:10.1029/2006GL028083, [abstract, full text]

Laut (2003), “Solar activity and terrestrial climate: an analysis of some purported correlations”, Journal of Atmospheric and Solar-Terrestrial Physics, Volume 65, Issue 7, May 2003, Pages 801-812, [abstract, full text]

Svensmark & Friis-Christensen (1997), “Variation of cosmic ray flux and global cloud coverage—a missing link in solar-climate relationships”, Journal of Atmospheric and Solar-Terrestrial Physics, Volume 59, Issue 11, July 1997, Pages 1225-1232, [abstract, full text]


3 Responses to “Revisiting Svensmark & Friis-Christensen (1997)”

  1. Bengt Andersson said

    You seem to be wrong in several ways.

    1. In more recent work of Svensmark looks for a correlation between cosmic rays and low cloud cover, not total. So your critic of SF97, though it seems to be valid, is outdated. Today, year 2010, not even Svenmark states that there is a correlation between cosmic rays and total cloud cover.
    2. In the work of Marsh and Svensmark (2000) you can find a correlation between low cloud cover and cosmic rays. They are not only using ISCCP but also the MODIS to “bridge” a step change in the ISCCP data set. There has been a lot of discussion about this recalibration of the satellite record and AGW proponents has declared Marsh and Svensmarks results as bogus due to this adjustment. In my opinion Evans (2007) confirms the problems that Marsh and Svensmark noticed and tried to solve by using alternative satellite records.
    3. The ISCCP data set from recent years have been used to debunk Svensmark hypothesis. Due to the problems shown in Evans (2007) this debunking is very questionable. The decline in recent years of the low cloud cover (that does not correlate with cosmic rays) could very well be an artifact from problems with viewing angles.
    4. There are independent measurements that show that there is a real correlation between clouds and cosmic rays, e.g. Harrison and Stephenson 2006. (
    5. Laut (2003) is totally irrelevant and is debunked by Svensmark. (

  2. Ari Jokimäki said

    1. First, my criticism is for the SF97, like I specifically stated. Second, the ISCCP problem shows in low cloud cover too, like Evan et al. (2007) said.

    2. Marsh & Svensmark (2000) made a “correction” but only to part of the data. They only fixed the part that didn’t agree with their results. Like I pointed out, I summarized the ISCCP problem recently, and it concerns the whole of ISCCP data, not just a brief time period in 1990’s. I have to wonder, when Marsh & Svensmark realized that there might be a problem in the data, why they didn’t check the whole of the data instead of just shifting the part that didn’t match their results to such that it matched their results.

    3. The ISCCP problem has to do with whole of ISCCP data, not just recent years. It has been shown here that the apparent correlation with cosmic rays in 1980’s, as presented by SF97, is based on faulty data and seems to vanish completely when the problem is accounted for.

    4. That’s not a global analysis, only regional – showing a weak effect. There is lot of research saying that the effect of cosmic rays to the climate is very weak, not significant.

    5. Svensmark doesn’t seem to say anything about the messiness of the graph, which was my point, to which I then noted that Laut had also noticed it. The DMSP data of late 1980’s doesn’t seem to support the ISCCP trend in that time (ISCCP dives strongly while DMSP shows a slight increase, this can be seen in the Svensmark’s reply you linked to). In fact, DMSP seems to fit rather nicely to the trend of regions with less problems in Evan et al., which shows a slight increase between 1987 and 1989 just like DMSP seems to do. That is why the messy outlook of the Figure in SF97 seems strange, especially as the figure is particularly messy in the parts where DMSP data is presented.

  3. Ari Jokimäki said

    There is an older blog article making the connection with ISCCP problems and cosmic rays:

    It’s curtains for cosmic rays – Nexus 6 (2007)

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