Lizards aren’t getting hotter faster than the planet after all, says retraction

EcographyA paper that raised alarms by suggesting lizards were warming even faster than the planet has been retracted after the authors employed the wrong method to measure temperatures.

Some scientists thought that, because of the way lizards retain heat to regulate their cold-blooded bodies, they might be more sensitive to temperature changes. Well, not in this case. The paper has been retracted from Ecography because the scientists erred in calculating the “radiative conductance of the animal” — basically, how much heat it can get rid of — such that the “broad-scale” conclusions of the study are invalid.

The notice for the aptly named paper “Lizards could be warming faster than climate” reads:

The above article, published online on 6th of February 2015 in Wiley Online Library (, has been retracted by agreement between the authors, the journal Deputy-Editor in Chief Nate Sanders, the Nordic Society Oikos and John Wiley and Sons Ltd.

The retraction has been agreed for the following reasons: an error of parameterization affected the results and therefore invalidated the broad-scale conclusions presented in the article. The article concluded that the operative temperature of a model lizard in the Iberian Peninsula should have increased 0.7°C more than air temperature during 1955–2000. Unfortunately, there was an error in the calculation of operative temperatures. Radiative conductance of the animal was calculated using air temperature (as in Bakken and Gates 1975, Campbell and Norman 1998, and Sears et al. 2011). However, instead of air temperature, Porter et al. (1973) and Bakken (1985) used body temperature. Using body temperature is more appropriate because the amount of thermal radiation emitted by a body is dependent on its temperature according to the Planck’s law. The authors tested if changing air temperature to skin temperature in the calculation of operative temperature changed the conclusions. It was found that when operative temperatures were calculated with body temperature it did not increase at a higher rate than air temperature, thus invalidating the conclusions in the study. Following the identification of the error in parameterization, the authors requested the retraction of the article. The authors and the editorial board of Ecography thank Professors Michael Kearney, Raymond Huey, and Warren Porter for bringing the issue to their attention.

When reached by email for a statement, author Francisco Ferri-Yáñez at the Museo Nacional de Ciencias Naturales, CSIC and Laboratorio Internacional en Cambio Global CSIC-PUC shared his side of the story:

I am a Phd student in the laboratory of Miguel Araujo and first author of the retracted article.

The brevia arose from a side project in which we took advantage of a dynamic downscaling of the climate of the Iberian Peninsula of the last 60 years to estimate the operative temperature of an ectotherm during that time period. The aim was to examine how the geographical patterns of air temperature and operative temperature and its relation with lizard distribution varied in space and time. Those analyses would be published in a more extensive article. After the examination of the results we found, quite unexpectedly, that operative temperature tended to increase more than air temperature. Miguel Araujo and I felt that this pattern stand on its own and that it was more convenient to publish it separately and that a brevia would be an appropriate format for it. Not many journals accept brevias, we first sent it to Frontiers in Ecology and Environment where it was rejected, and then decided to submit it to Ecography, where it was finally accepted.

Soon after its publication, we received an e-mail from Professor Michael Kearney (which included Raymond Huey and Warren Porter) expressing his concerns about the equations used to calculate operative temperature. In particular, he expressed most concern for the fact that we used Air temperature to estimate radiative heat loss while he considered that we should have used body temperature. Using skin temperature (which can be replaced for body temperature, when considering a small organism, which was the case) is computationally more challenging as you need as an input the same variable that you want to calculate, this problem can be solved by approximating a steady state solution using an iterative procedure. Fortunately, Professor Kearney was also kind enough to provide an R-script which calculated operative temperature doing just that.

After reviewing the sources of the equations for operative temperature provided in Bakken 1975, I noticed that indeed, the original formulation used surface temperature to calculate the radiative exchange. In other posterior reformulations of operative temperature air temperature was used, considering that when the difference between air and skin temperature is not very large, the error is neglegible.

I then recalculated the operative temperature for the whole period using the script provided by Professor Kearney and found that contrary to our previous result operative temperature it did not increase faster than air temperature. After repeating the analysis, we concluded that the results of the article did not hold. We then had to decide if we needed to send a corrigendum, an erratum or to retract the brevia. In this case, the publication of the brevia was done because of the pattern found, and as we concluded that this pattern was not real the appropriate course of action would be to retract the article.

We contacted the journal’s managing editor, who said she didn’t have anything to add to the note.

With reporting by Shannon Palus

Hat tip: Rolf Degen

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5 thoughts on “Lizards aren’t getting hotter faster than the planet after all, says retraction”

  1. This merely identifies one of the problems with science: publishing only papers that show positive and not negative results. Instead of retraction, I think it would have been better for them to publish the update, showing that they had recalculated, and found no effect.

    Publishing only positive results can skew the scientific literature. This is an issue that goes beyond this particular paper. Anyways, my 2 cents.

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