There is a fairly weird paper entitled Suggestive correlations between the brightness of Neptune, solar variability, and Earth’s temperature by Hammel and Lockwood. Why is it weird? Various reasons, which I’ll try to explain here as best I can, but it really needs someone who knows more about it. These are more notes in case anyone out there feels interested to look.

First off, none of their correlations are significant, a fact which does rather disappoint them: Although correlations between Neptune’s brightness and Earth’s temperature anomaly–and between Neptune and two models of solar variability–are visually compelling, at this time they are not statistically significant due to the limited degrees of freedom of the various time series. but they don’t let that put them off: Nevertheless, the striking similarity of the temporal patterns of variation should not be ignored simply because of low formal statistical significance. Notice the word “formal” they have put in there… they are trying to say that we shouldn’t let a formality like lack of significance get in the way of a nice idea. Thats the abstract; within the article text they rather cutely say Low formal statistical significance does not mean the correlations we find are in fact spurious, only that we cannot demonstrate otherwise. What would science be like if all referees let people get away with stuff like that? Later they just about manage to struggle up to 20% sig, but that appears to be based on some rather odd stuff: “We assume four degrees of freedom for the decades long Neptune data set, based on the number of zero crossings in the residual plots in Figure 4.” I don’t understand why thats a valid method of counting DOF (this is after they have removed a 2nd-order poly from the various datasets). Also they have selected a lag of 17 years between the datasets in order to maximise the correlations, and the sig tests they are using don’t account for this.

Second point is the solar irradiance data they use, which shows a rising trend from 1960; and a rising trend from 1980; and looks like nothing I recognise, though they source it to Foukal 2002.

Their reasons for 11-y filtering of solar; and for 11-y filtering of Earth but not Neptune temps; are not terribly well explained.

[Update: I continue to poke at this. So, the paper refs The nature of Neptune’s increasing brightness: evidence for a seasonal response by Sromovsky et al. which happens to be online. That paper says the combined disk-averaged variation from 1972 to 2002 is consistent with a simple seasonal model having a hemispheric response delay relative to solar forcing of 30 years.H&L say oh yes, but its not consistent with pre-1970 data. So look again at H&L and indeed there is a break: their Neptune data is two series, with a break between 1965-ish and 1970. I can’t quite tell what the difference is, but one obvious question is why S et al didn’t use the earlier data? Is it consistent with the later? S et al. note the earlier measurement but say the nominal B filter (Lockwood and Thompson 2002) spans a wavelength range from 390 to 500 nm (half-maximum points), which is about five to six times the width of the b filter and is much more heavily weighted toward shorter wavelengths, with a peak response near 412 nm… and it will take someone who knows these things (hello Stein? Jon?) to work it out.

The other interesting point is that S et al. note the strong latitudinal variation in the brightening – they ignore this in constructing their theory though .

An another maybe interesting paper is, L&J 2006 which says The apparent relationship between Neptune’s brightness variation and the 11-year solar cycle seen in cycles 21 22 (1972 1996) has apparently now faded away. – a lesson on troubling yourself about stat sig perhaps, since L now seems to be removing the 11y cycle entirely. Who knows what next years theory might be? -W]

[Update: Tamino looks at the use of the Foukal TSI record in this study and concludes that it cannot validly be used -W]

[Uupdate: some RSS problems may now be fixed… odd non-std CR’s -W]


  1. #1 uBeR

    It looks like WCR beat you to it, but with a different spin on it…

    [Yes, oddly enough WCR is so short of space it didn’t find space to mention the lack of significance in the correlations> Or maybe the lack of sig wasnt considered sig? Who cares about stats anyway! -W]

  2. #2 guthrie

    Can you explain a little bit more what filtering is? I can see that doing something over 11 years for the earth and 17 for Neptune is a bit silly sounding, even when I don’t know exactly what it is that is being done, but it would be nice to know.
    Also why on earth do they get away with trying to maximise the correlation by using different sets of years anyway?

    [Sorry, I may have mislead you. The 17 years is a lagged correlation (not the filtering). There is nothing intrinsically wrong with looking at correlations at different lags, but… it affects the statistics. If you pick 2 time series, and test for sig corr, then the stats are fair. If you take 2 series and go through picking the best lag, then the stats are no longer fair – you will get more false sigs. But since they appear to have picked an arbitrary 4 DOF, this may all be moot (they have 4-5 decades smoothed with an 11-y filter which sounds like 4-5 DOF to me; they remove a second-order poly which presumably removes 2 more; so they have little left.

    As for the filtering: they are rather unclear on this. Some 9all) of their time series have an 11-year filtering/smoothing applied to them, “to remove the solar cycle” -W]

  3. #3 Andrew Dodds


    Given that there are 8 other planets, and multiple solar proxies, and multiple measurements you can make on the other planets, surely they should be able to come up with something a bit better than that..

    Have to admit that I didn’t realise that you could get published for observing a lack-of relationship. This could make an academic career so much simpler.

    Basic neptune info.. (Note: ‘Great dark spot has vanished’!).

    Springtime on Neptune (at least in the south):

  4. #4 Nathan Rive

    If there was any doubt that it can be easy to get past the peer review process, check out these choice quotes from a recent article in Energy Policy:

    “Cars with backseats are purchased solely to get lower insurance rates, and only dogs use these backseats.”

    “After you retire, privacy turns into loneliness, and a need for communication forces you to realize that you have misplaced your life values.”

  5. #5 Ian

    There was an interesting post on this general issue – AGW on earth and supposed solar-induced changes in some other bodies in the solar system – at Bad Astronomy a while back:

  6. #6 Eli Rabett

    FWIW, the solar energy input at Neptune is less than the radiative emission from the planet probably mostly from gravitational infall, but maybe from icy comets striking the planet.

    [I didn’t know that… but presumably H&L did. Can comets explain the bright bands? -W]

  7. #7 Eli Rabett

    Sure look what happened when s-l hit jupiter. persistence is another issue, but n is a lot colder.

  8. #8 maksimovich

    the bright bands?


  9. #9 Eli Rabett

    Spring. The whole damn thing is spring

    [Possibly. But H&L do have a reply to that: the early data don’t fit the seasonal model of S (OTOH the early data is possibly not homogeneous – they don’t really address that). Also they put some faith in the (not very sig) decadal correlations between N and Earth -W]

  10. #10 inel

    Hi William,

    Completely off-topic, I came by to see if you had written about the latest paper by Lockwood and Frohlich, and ended up here, on the wrong (i.e. G.W. Lockwood) page!

    Well, Mike Lockwood and Claus Frohlich have a paper that you might be interested to hear about, if only as an update to the infamous IoP seminar a month ago. This paper was mentioned by Alan Thorpe, but not yet published back then. You can read more on ‘No solar hiding place for greenhouse sceptics‘, with a link to Nature that I cannot access, but I expect you can :-)

    [Sadly I don’t have premium access, but someone lese does. I’ll write a little post on it -W]

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