On the Potential Extinction of High-Elevation Species

In his highly-hyped 26 April 2007 testimony before the Select Committee of Energy Independence and Global Warming of the U.S. House of Representatives entitled "Dangerous Human-Made Interference with Climate," NASA's James Hansen stated that life in alpine regions is "in danger of being pushed off the planet" in response to continued anthropogenic-induced global warming. Why? Because that's what all the species distribution models or SDMs predicted at the time. However, a set of new-and-improved models has raised some serious questions about this overly zealous contention.

The concept behind the newer models, described by Randin et al. (2009), is such that "the mean temperature interpolated from local stations at a 20-meter resolution contains more variability than expressed by the mean temperature within a 50-km x 50-km grid cell in which variation in elevation is poorly represented." Or as they described it in another part of their paper, "climatic differences along elevation gradients, as apparent at 25-m x 25-m resolution allow plant species to find suitable climatic conditions at higher elevation under climate change," whereas "models at a 10 x 10' resolution [10 minutes of latitude x ten minutes of longitude, which correspond to 16-km x 16-km cells in the Swiss Alps, where they carried out their analyses] reflect the mean climatic conditions within the cell, and thus provide imprecise values of the probability of occurrence of species along a thermal gradient."

In testing this "local high-elevation habitat persistence hypothesis," as they described it, the group of Swiss, French and Danish researchers of Randin et al. assessed "whether climate change-induced habitat losses predicted at the European scale (10 x 10' grid cells) are also predicted from local-scale data and modeling (25-m x 25-m grid cells)." In doing so, they found that for 78 mountain species modeled at both European and local scales, the "local-scale models predict persistence of suitable habitats in up to 100% of species that were predicted by a European-scale model to lose all their suitable habitats in the area."

In discussing their findings, Randin et al. suggested that the vastly different results they obtained when using fine and coarse grid scales might help to explain what they called the Quaternary Conundrum, i.e. "why fewer species than expected went extinct during glacial periods when models predict so many extinctions with similar amplitude of climate change (Botkin et al., 2007)." In addition, they noted that "coarse-resolution predictions based on SDMs are commonly used in the preparation of reports by the Intergovernmental Panel on Climate Change," which are then used by "conservation planners, managers, and other decision makers to anticipate biodiversity losses in alpine and other systems across local, regional, and larger scales."

In light of this large-scale usage of coarse-grid analyses of species responses to climate change, it is important that both public and private policies are not based on the findings of such studies. All they do is provide a pseudo-scientific basis for folks such as NASA's James Hansen to feed their faulty predictions to decision makers at the highest levels of government, all in the guise of what they portray to be sound science, which they clearly are not.

Additional References
Botkin, D.B., Saxe, H., Araujo, M.B., Betts, R., Bradshaw, R.H.W., Cedhagen, T., Chesson, P., Dawson, T.P., Etterson, J.R., Faith, D.P., Ferrier, S., Guisan, A., Hansen, A.S., Hilbert, D.W., Loehle, C., Margules, C., New, M., Sobel, M.J. and Stockwell, D.R.B. 2007. Forecasting the effects of global warming on biodiversity. BioScience 57: 227-236.