Is the Report Linking the Extinction of Frogs with Global Warming a Scientifically Balanced Conclusion?

I read the media reports linking global warming to the extinction of frogs with considerable skepticism. (e.g. in the Washington Post). I was even more surprised when I read the first author’s comments on the Nature paper that the media reports are based on.

As written on this weblog (see What is the Relevance of a Tropical Average Surface Temperature Change to Organisms in the Tropics?), large scale surface temperature averages, even if they were robust, are not what frogs experience in their immediate environment ). The Nature article is contrary to this perspective.

The article By Juliet Eilperin, Washington Post Staff Writer,
is headlined

“Warming Tied To Extinction Of Frog Speciesâ€?

And includes the statements

“Rising temperatures are responsible for pushing dozens of frog species over the brink of extinction in the past three decades, according to findings being reported today by a team of Latin American and U.S. scientists.â€?

and

“….the new study documents for the first time a direct correlation between global warming and the disappearance of around 65 amphibian species in Central and South America.â€?

The lead author, J. Alan Pounds, of the Nature article which is the basis for the news article, is reported in the Washington Post article as stating

“”Disease is the bullet killing frogs, but climate change is pulling the trigger,” Pounds said. “Global warming is wreaking havoc on amphibians and will cause staggering losses of biodiversity if we don’t do something first.”

and

“’There’s a coherent pattern of disappearances, all the way from Costa Rica to Peru,’ Pounds said in an interview. ‘Here’s a case where we can show that global warming is affecting outbreaks of this disease.’”

In the Nature abstract , it says,

“As the Earth warms, many species are likely to disappear, often because of changing disease dynamics. Here we show that a recent mass extinction associated with pathogen outbreaks is tied to global warming. Seventeen years ago, in the mountains of Costa Rica, the Monteverde harlequin frog (Atelopus sp.) vanished along with the golden toad (Bufo periglenes). An estimated 67% of the 110 or so species of Atelopus, which are endemic to the American tropics, have met the same fate, and a pathogenic chytrid fungus (Batrachochytrium dendrobatidis) is implicated. Analysing the timing of losses in relation to changes in sea surface and air temperatures, we conclude with ‘very high confidence’ (> 99%, following the Intergovernmental Panel on Climate Change, IPCC) that large-scale warming is a key factor in the disappearances. We propose that temperatures at many highland localities are shifting towards the growth optimum of Batrachochytrium, thus encouraging outbreaks. With climate change promoting infectious disease and eroding biodiversity, the urgency of reducing greenhouse-gas concentrations is now undeniable.”

In the Nature news release , which is titled “Dead frogs linked to global warming”, it says,

‘Pounds hopes his team’s findings will ram home the global-warming message. ‘We have to reduce concentrations of greenhouse gases very soon if we are to avoid massive losses of biodiversity.’”

This claim, however, is not scientifically sound as it does not explore the relative role of other reasons for the extinctions and loss of biodiversity. This is hardly how balanced scientific work should be performed.

As Tom Stohlgren has informed me (Dr. Stohlgren is an internationally respected ecologist who studies invasive plant species), chytrid fungus (an invasive disease) is by far the number one cause of amphibian decline in the world. According the ISI Web of knowledge, Dr. Stohlgren found that there are over 90 peer-reviewed publications on the role of chytrid disease in amphibian decline.

Possible reasons for the increase for the prevalence of chytrid disease and its role in the decline in frog populations include the effect on the local weather of landscape change in the region where the frogs live. We have shown in several papers that landscape change in Costa Rica has had a major effect on the climate of this region, including the rain forest. These papers are

Nair, U.S., R.O. Lawton, R.M. Welch, and R.A. Pielke Sr., 2003: Impact of land use on Costa Rican tropical montane cloud forests: 1. Sensitivity of cumulus cloud field characteristics to lowland deforestation. J. Geophys. Res. – Atmospheres, 108, 10.1029/2001JD001135.

Lawton, R.O., U.S. Nair, R.A. Pielke Sr., and R.M. Welch, 2001: Climatic impact of tropical lowland deforestation on nearby montane cloud forests. Science, 294, 584-587.

Ray, D.K., U.S. Nair, R.O. Lawton, R.M. Welch, and R.A. Pielke Sr., 2006: Impact of land use on Costa Rican tropical montane cloud forests. Sensitivity of orographic cloud formation to deforestation in the plains. J. Geophys. Res., 111, doi:10.1029/2005JD006096.

These studies, which the authors acknowledge in the Nature paper but do not accept their conclusions, indicate that a local human intervention is a major contributor to altering the immediate environment of the frogs. Since tropical landscape continues unabated (e.g. see Table 1 in Pielke Sr., R.A., J.O. Adegoke, T.N. Chase, C.H. Marshall, T. Matsui, and D. Niyogi, 2005: A new paradigm for assessing the role of agriculture in the climate system and in climate change. Agric. Forest Meteor., Special Issue, in press. ) this certainly must be affecting the viability of frog populations.

For further discussion of the Nature paper, the weblog published by the worldclimatereport is worth reading (Jumping To Conclusions: Frogs, Global Warming and Nature)

We need to move beyond the over simplistic view of global warming as being the dominant cause of the demise of the frogs (or other enviromental threats). The spectrum of risks to frog population (their vulnerability), including global warming, need to be presented and assessed for their relative importance. This was not done in the Nature study. Moreover, reporters need to more objectively assess whether a paper was used to advance an agenda (in this case as clearly stated by the lead author), or is actually a balanced scientific study. We certainly should be concerned about declining populations of amphiphians, but we do not serve those who are seeking to alter this decline but focusing on just one possible environmental explanation.

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