Volume 11, Number 16: 16 April 2008
In a paper recently published in Global Ecology and Biogeography, Javier Seoane and Luis Carrascal of the Museo Nacional de Ciencias Naturales in Madrid, Spain, write that "global climatic change has been proposed as one of the most likely environmental processes governing population trends," stating more specifically that "it has been hypothesized that species preferring low environmental temperatures, which inhabit cooler habitats or areas, would be negatively affected by global warming as a consequence of the widely accepted increase of temperature during the last two decades," while additionally noting that "this effect is assumed to be more intense at higher latitudes and altitudes because these areas seem to be changing more rapidly." Hence, they devised a study "to assess whether population changes agree with what could be expected under global warming (a decrease in species typical of cooler environments)," focusing on birds.
Working in the Spanish portion of the Iberian Peninsula in the southwestern part of the Mediterranean Basin, the two researchers determined breeding population changes for 57 species of common passerine birds between 1996 and 2004 in areas without any apparent land-use changes. This work revealed, in their words, that "one-half of the study species showed significant increasing [our italics] recent trends despite the public concern that bird populations are generally decreasing," while "only one-tenth showed a significant decrease."
In discussing their findings, Seoane and Carrascal state that "the coherent pattern in population trends we found disagrees [our italics] with the proposed detrimental effect of global warming on bird populations of western Europe." And they are not the only ones to have come to this conclusion. They note, for example, that "one-half of terrestrial passerine birds in the United Kingdom exhibited increasing recent trends in a very similar time period (1994-2004)," citing Raven et al. (2005); and they note that "there is also a marked consistency between the observed increasing trends for forest and open woodland species in the Iberian Peninsula and at more northern European latitudes in the same recent years," citing Gregory et al. (2005). Likewise, they write that "Julliard et al. (2004a), working with 77 common bird species in France, found that species with large ecological breadth showed a tendency to increase their numbers throughout the analyzed period."
In further commenting on their findings, Seoane and Carrascal say that in their study, "bird species that inhabit dense wooded habitats show striking patterns of population increase throughout time." Noting that "this is also the case with those bird species mainly distributed across central and northern Europe that reach their southern boundary limits in the north of the Iberian Peninsula," they speculate that "these short- to medium-term population increases may be due to concomitant increases in productivity," citing the thinking of Julliard et al. (2004b) and the empirical observations of Myneni et al. (1997), Tucker et al. (2001), Zhou et al. (2001), Fang et al. (2003) and Slayback et al. (2003), whose work figures prominently in establishing the reality of the late 20th-century warming- and CO2-induced greening of the earth phenomenon, which has produced, in the words of the Spanish scientists, "an increase in plant growth or terrestrial net primary production in middle latitudes of the Northern Hemisphere since the 1980s, particularly in forest environments."
It should be clear from these several observations that the supposedly unprecedented warmth of the last two decades has not led to what Seoane and Carrascal call "the proposed detrimental effect of global warming on bird populations of western Europe." In fact, it appears to have done just the opposite, with a little help, we might add, from one of man's and nature's very best friends: the contemporary rise in the air's CO2 content.
Sherwood, Keith and Craig Idso
References
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Gregory, R.D., van Strien, A.J., Vorisek, P., Gmelig Meyling, A.W., Noble, D.G., Foppen, R.P.B. and Gibbons, D.W. 2005. Developing indicators for European birds. Philosophical Transactions of the Royal Society B: Biological Sciences 360: 269.
Julliard, R., Jiguet, F. and Couvet, D. 2004a. Common birds facing global changes: what makes a species at risk? Global Change Biology 10: 148-154.
Julliard, R., Jiguet, F. and Couvet, D. 2004b. Evidence for the impact of global warming on the long-term population dynamics of common birds. Proceedings of the Royal Society B: Biological Sciences 271: S490-S492.
Myneni, R.C., Keeling, C.D., Tucker, C.J., Asrar, G. and Nemani, R.R. 1997. Increased plant growth in the northern high latitudes from 1981 to 1991. Nature 386: 698-702.
Raven, M.J., Noble, D.G. and Baillie, S.R. 2005. The Breeding Bird Survey 2004. British Trust for Ornithology, Thetford, UK.
Seoane, J. and Carrascal, L.M. 2008. Interspecific differences in population trends of Spanish birds are related to habitat and climatic preferences. Global Ecology and Biogeography 17: 111-121.
Slayback, D., Pinzon, J. and Tucker, C. 2003. Northern hemisphere photosynthetic trends 1982-1999. Global Change Biology 9: 1-15.
Tucker, C.J., Slayback, D.A., Pinzon, J.E., Los, S.O., Myneni, R.B. and Taylor, M.G. 2001. Higher northern latitude NDVI and growing season trends from 1982 to 1999. International Journal of Biometeorology 45: 184-190.
Zhou, L., Tucker, C.J., Kaufmann, R.K., Slayback, D., Shabanov, N.V. and Myneni, R.B. 2001. Variations in northern vegetation activity inferred from satellite data of vegetation index during 1981 to 1999. Journal of Geophysical Research 106: 20.069-20,083.