I am so close to deleting my ResearchGate profile

Yesterday, it a fit of procrastination, I updated my ResearchGate profile, adding recently published papers.

I wish I hadn’t bothered.

Today I have been deluged (and I exaggerate only slightly – OK, perhaps more than slightly) with requests for copies of one of these papers.

This paper isn’t available only in the University of Bergen library in the bottom of a locked filing cabinet stuck in a disused lavatory with a sign on the door saying “Beware of The Leopard”.

Nor does it languish behind Elsevier’s monstrous paywalls.

It is in an open-access journal, available to read by anybody who cares to click on this link. Except that ResearchGate does not provide that link nor any other, instead it encourages readers to “request full-text” from me. Why? To encourage me to upload a copy of my paper to halt the requests. Why? I have no idea – I cannot see that it serves any useful purpose to host a copy of an open-access paper on ResearchGate.

While I am gratified that so many people are interested in reading my work, ResearchGate could have lightened the load on my email by simply linking to my paper.

Posted in Uncategorized | Tagged | 6 Comments

CFC concentrations not emissions affect ozone

Steve Goreham has written something for WUWT. That is enough to know it is going to be bad. How bad? This bad:

Another year has passed and that stubborn Ozone Hole over Antarctica refuses to go away. Data from the National Aeronautics and Space Administration (NASA) shows that the Ozone Hole for the fall maximum season grew 22 percent from 2014 to 2015. World consumption of Ozone Depleting Substances has been reduced to zero over the last three decades, but the Ozone Hole is as large as ever. Did humans really save the ozone layer?

CFC emissions and ozone hole area

CFC emissions and ozone hole area

Goreham argues that the persistence of the ozone hole after CFC emissions reduced suggests that the ozone hole is natural. In reality, it shows that CFC are persistent pollutants.

Contrary to Goreham’s argument, CFC emissions do not directly affect ozone, rather atmospheric CFC concentrations do. CFC concentrations integrate emissions since CFC emissions began, less cumulative  degradation of CFC. Atmospheric CFC concentrations are available from the Carbon Dioxide Information Analysis Center.

Southern hemisphere CFC concentrations

Southern hemisphere CFC concentrations

CFC concentrations are falling now that emissions have (mostly) ceased, but due to the long atmospheric lifespan of these gases, concentrations have only fallen slightly. CFC12 concentrations, for example, have fallen by less than 5%. Thus, if the ozone hole was driven by CFC12 alone, we would expect it to have have decreased by about 5%, rather than shrinking to zero as Goreham naïvely expects.

With the long atmospheric lifespan of CFCs, Goreham will have many more opportunities to show his willful ignorance.

Posted in Fake climate sceptics, WUWT | Tagged , | 13 Comments

You don’t have to explain everything

So many papers present interesting palaeo-data and then add a badly done analysis that attempts to prove that the palaeo-data correlate (if you squint hard enough) with the Carriaco Basin record, NGRIP or the solar insolation reconstruction. This is not a good state of affairs: no amount of correlation-by-eye or bodged spectral analysis will ever provide evidence of anything.

I don’t know why authors feel compelled to do this. Perhaps they think they cannot publish their record without making the paper “sexy” by explaining the record in terms of climate forcings or correlations with other records.

It doesn’t have to be this way. Wilhelm et al have a new millennium-long flood record under review at Climate of the Past Discussion in which they explicity decline to try to explain the record with external forcings with simplistic analyses.

… external forcing such as solar activity, and volcanic eruptions largely varied over the last millennium (e.g. Servonnat et al., 2010; Delaygue et Bard, 2011; Gao et al., 2012; Crowley and Unterman, 2013) and their non-linear combination also with the greenhouse gases may result in different time-space temperature patterns and, thereby, in different flood responses during these two periods. In order to explore forcing-dependent impacts on the climate–flood relationships, deeper analysis utilizing for example advanced statistics or simulations is required.

I just hope the reviewers won’t require them to test for correlations with forcings.

Posted in Palaeohydrology, Peer reviewed literature | Tagged | 1 Comment

Doubling down on nutations

Kelsey et al have replied to Eric Wolff’s comment on their Climate of the Past Discussion Paper which I discussed yesterday. Wolff is concerned that the paper’s opening statement that “The existence of a ~1470 year cycle of abrupt climate change is well-established” does not reflect recent literature, citing multiple papers to make this point.

Kelsey’s response is “Please see references from highly ranked publications referenced in this article” followed by a list of papers (one of which, as Wolff points out in his subsequent reply, does not exist). This is not a response that indicates she is open to input from reviewers.

But what about these nutations which Kelsey et al think are, together with sunspots, driving the DO cycles. Nutations are wobbles in the Earth’s orbit caused by the gravitational pull of the Sun and the Moon on the Earth’s equatorial bulge. This wobble will cause a redistribution of insolation over the Earth, just like the obliquity and precession components of Milankovitch cycles. The key question is by how much? Is it enough, in conjunction with sunspots, to cause the DO cycles? The paper does not explore this critical question.

For reference, the obliquity cycle changes the angle at which the Earth’s angle tilts from 22.1° and 24.5°. The latitudinal component of the 18.6-year nutation is ±9.2″ (i.e. 9.2/60/60 = ±0.0025°). This causes the Tropic of Cancer (where the Sun is directly overhead at noon on the summer solstice) to move by a few hundred metres. It should be fairly obvious that insolation does not vary appreciably over such short distances. Nutation will also be linked to some changes in tidal amplitude, but it is really hard to imagine an 18.6-year cycle having much effect on millennial timescales.

I had expected A. M. Kelsey to be a retired engineer. Actually, she is a PhD student at the University of Queensland studying the palaeoecology and palaeoclimatology of Fraser Island in southern Queensland. Her coauthors are her supervisors – who I think are somewhat remiss for allowing her to submit this paper.

Why am I interested in this dubious paper? Three main reasons:

  • If nutations and sunspots caused DO cycles then our climate is far more sensitive to forcings than anybody thinks it is.
  • Climate change deniers will probably use it to argue our climate is only sensitive to sunspots and nutations and that greenhouse gas forcings are somehow insignificant.
  • The open peer review process at Climate of the Past gives a window onto how peer review copes with “interesting” papers.
Posted in Peer reviewed literature | Tagged , | 1 Comment

Numberology or Physics?

A new paper by Kelsey et al at Climate of the Past Discussions is attempting to explain the apparent 1470 year periodicity of the Dansgaard–Oeschger and Bond cycles with sunspot cycles, lunar cycles and the anomalistic year.

I predict there are going to be quite a few comments. Eric Wolff has already left one pointing out that the paper’s opening sentence “The existence of a ~1470 year cycle of abrupt climate change is well-established” is not well supported by the recent literature and revisions to the ice-core chronology.

Wolff writes “I leave it to others to assess whether the periodicity in astronomical cycles proposed by the authors could be expected to have any climatic effect, and specifically the one that is observed at D-O timescales.”

Indeed. Certainly the authors don’t address this critical problem in the paper.

The authors seem to be more interested in showing that the cycles they derive from the anomalistic year – “the time Earth’s rotation and revolution (RRA) relative to the perihelion, i.e. the time for perihelion to occur over the same geographic longitude on Earth” – have counterparts in the 14C record. It is not obvious that this is expected.

Posted in Peer reviewed literature | Tagged , | 1 Comment

You cannot smooth your way to significance

Imagine you have three 73-year long instrumental climate records that you want to correlate with solar activity in the last century. The instrumental records are noisy so you smooth them with a five-year moving average, and then you note that the correlation can be improved by lagging one of the records by two years behind the solar signal. Should you be excited by a correlation of -0.47, the strongest of the three correlations?

The authors, Czymzik et al, of a new paper in Climate of the Past Discussions were. They claim that the correlation of -0.47 has a probability of less than 0.0001 of occurring by chance if there is no relationship between the instrumental record and solar activity. A correlation this strong and a p-value so low would be impressive evidence of the importance of solar forcing in the last century, except that they are probably data processing artefacts.

Lets start by looking at the effect of smoothing the data with the moving average. I’m going to take two time-series of 73 random numbers, smooth them with a five-point moving average, and then find the correlation between the two time-series. I’m going to repeat this many times to find the distribution of correlations expected by chance with this data processing.


x5<-running(x, width=5, fun=mean)

  y5<-running(y, width=5, fun=mean)


quantile(res, prob=c(0.025, 0.975)) 


The 95% significance interval of the correlation of the time series processed with a moving average is ±0.375 (by comparison, the 95% significance interval on the original time series would be ±0.230). The observed correlation of -0.47 has a p-value of about 0.01, two orders of magnitude less extreme than reported by the paper, but still significant at p = 0.05. The smoothing has induced strong autocorrelation in the data, so the test that the authors use, which assumes that the observations are independent, is extremely liberal. By ignoring the induced autocorrelation, assuming they still have 73-2 degrees of freedom, the authors have generated a seriously misleading idea of how strong their evidence is. And I’ve not finished yet.

Next I want to consider how allowing for different lags (correlating this year’s climate data with solar data from the last year (lag 1) or the year before (lag 2)) affects the p-value. Allowing for lags is not absurd – a recent paper in Environmental Research Letters found a three-year lag between solar activity and the North Atlantic Oscillation in a climate model run. Czymzik et al test for correlations at lags from -5 to +5. Making the assumption that only lags 0-3 are physically reasonable, I modified the above code to output the maximum correlation at these lags. This is to be generous, the results would be much worse if I considered all 11 lags.

  y5<-running(y, width=5, fun=mean)
  c(c0, c1, c2, c3)[which.max(abs(c(c0, c1, c2,c3)))]


quantile(res2, prob=c(0.025, 0.975))


Now the 95% significance level is at ±0.447 and the p-value of the best correlation reported is 0.035. The other two correlations are not significant (p > 0.1). So rather than having three very highly significant correlations, Czymzik et al have one marginally significant correlation.

But even this is optimistic, we also ought to consider multiple testing (three instrumental records, two versions of each) and the effect of autocorrelation in the raw data. If we take these into account, it is unlikely that any of the correlations with instrumental records reported by Czymzik et al are statistically significant.

The second part of Czymzik et al reports the correlation between flood frequency reconstructed from the sediments of the lake Ammersee in southern Germany and cosmogenic isotopes to try to infer the role of solar activity. Czymzik et al finds high correlations: 0.36 with 14C production rate, and 0.45 with 10Be concentations. The significance of these correlations is almost certainly over-estimated but it is unclear how exactly they were calculated: I don’t dispute that they are significant. I do find it strange that the authors have chosen to correlate their flood frequency record with the isotope production rate/concentration rather than estimates of total solar irradiation (Steinhilber et al 2012) or solar modulation (Muscheler et al 2007). The problem with the isotope data is that concentration and production rates are affected by both the solar magnetic field (which varies with solar activity) and the geomagnetic field. The geomagnetic field mainly varies on long timescales, giving trends in the isotope data that were removed by Steinhilber et al and Muscheler et al. I cannot think of a good reason not to use these reconstructions of solar activity (but I can think of a bad reason).

Czymzik et al is in open review at Climate of the Past Discussions. I’ll keep an eye on the reviewers’ comments to check they cover the points I raise here (and some problems with the spectral analysis).

There are some good papers looking for evidence of solar activity on palaeoclimate records. This is not one of them.

Posted in Peer reviewed literature, solar variability | Tagged | 4 Comments

Estimating unbiased transfer-function performances in spatially structured environments

Mathias Trachsel and I have a paper in open discussion at Climate of the Past Discussions developing methods for estimating the performace of transfer functions in spatially autocorrelated environments. The paper began life as a blog post a couple of years ago which proposed the methods. The paper uses lots of simulated species data, with known spatial properties, to test how well the methods work.

Abstract. Conventional cross-validation schemes for assessing transfer-function performance assume that observations are independent. In spatially-structured environments this assumption is violated, resulting in over-optimistic estimates of transfer-function performance. H block cross-validation, where all samples within h km of the test samples are omitted is a method for obtaining unbiased transfer function performance estimates. In this study, we assess three methods for determining the optimal h. Using simulated data, we find that all three methods result in comparable values of h. Applying the three methods to published transfer functions, we find they yield similar values for h. Some transfer functions perform notably worse when h block cross-validation is used.

We think the methods perform fairly well – certainly we would recommend using them rather than ignoring spatial autocorrelation in strongly spatially structured calibration sets. Examples of how to run the tests will be in a vignette in the next version of the palaeoSig R package.

Trachsel, M. and Telford, R. J.: Technical Note: Estimating unbiased transfer-function performances in spatially structured environments, Clim. Past Discuss., 11, 4729-4749, doi:10.5194/cpd-11-4729-2015, 2015.

Posted in transfer function | Tagged | Leave a comment