Tuesday, June 15, 2010

Butterflies 'fly early as planet warms...then again probably not

ABC provided extensive coverage (see HERE) of a Biology Letters paper titled "Early emergence in a butterfly causally linked to anthropogenic warming" in March. A comment challenging the claims of the paper has now been published online by Biology Letters. Will ABC now update their coverage?

The comment includes the following statements:
"I have obtained the same data used in this study as Kearney et al. and am unable to confirm the results for the historical observation data. I count 239 observations made in Oct-Dec from 1942 to 2009. The annual data show a wide range of earliest observation dates (Figure 1), and at face value the use of 5 year or 10 year averages appears to be a convenient statistical method that hides the very wide spread of observation dates."
"Using this "opportunistic" data to establish emergence is like dating a volcanic eruption based on collection dates of samples housed in a museum. The historical trends identified simply reflect variation in the time collectors have ventured out to observe and collect butterflies. "
"There remains considerable temporal bias in the data, with over 50% of total observations post dating 1990. There is also a considerable bias in observation locations, with the vast majority collected in Melbourne's east and none in the vicinity of Laverton, the weather station that was used to characterise temperature change over the whole of the study area (Figure 2)."
"The paper does not mention well documented Urban Heat Island effects over Melbourne that encompasses Laverton that have clearly affected temperature at this station over the period of study (see Morri and Simmonds, 2000 and Torok et al., 2001). Close examination of other stations in the study area shows a wide variety of temperature trends (Figure 2). It seems the authors have chosen one station that favours their theory without adequately explaining why others should be rejected. "
"Based on these points, I believe that the authors' conclusions remain unsupported by the data presented."

Copies of figures that accompany the Biology Letters comment appear below. 
Figure 2 below. Location of H.Merope observations (black dots)-note concentration east of Melbourne CBD and absence of observations near Laverton. Extent of urban development around Melbourne indicated by pink shading. Creeks and rivers shown as blue lines. Topographic contours at 50 m intervals (brown lines) provide an indication of topographic variability over study area, marked by the black outline. Selected  weather stations shown as red squares with corresponding historical April-October mean temperature  readings obtained from the Australian Bureau of Meteorology shown around the outside-note variation in temperature trends across the study area, including some negative.

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