Background
In his 26 April 2007 testimony before the U.S. House of Representatives' Select Committee on Energy Independence and Global Warming, NASA's James Hansen stated that life in alpine regions is in danger of being "pushed off the planet" in response to global warming that encourages upward migration on mountains.

What was done
In a study that comes to bear on this contention, the authors revisited areas of twelve mountains having summits located between elevations of 2844 and 3006 meters in the canton of Grisons, Switzerland, where in 2004 they made complete inventories of vascular plant species that they compared with similar inventories made by other researchers in 1885, 1898, 1912, 1913 and 1958, following the ascension paths of the earlier investigators "as accurately as possible," and where mean summer temperature increased by at least 0.6°C between the time of the first and current study.

What was learned
The upward migration rates detected by Holzinger et al. were on the order of several meters per decade; and their data suggested that vascular plant species richness increased by 11% per decade over the last 120 years on the mountain summits (defined as the upper 15 meters of the mountains) in the alpine-nival ecotone. This finding, in their words, "agrees well with other investigations from the Alps, where similar changes have been detected (Grabherr et al., 1994; Pauli et al., 2001; Camenisch, 2002; Walther, 2003; Walther et al., 2005)."

With respect to the prediction of "the extinction of a considerable number of high-alpine species" within "the context of climate warming," they say that this "outstanding threat for species to become out-competed 'beyond the summits' can neither be confirmed nor rejected with our data."

What it means
Once again, the "outstanding threat" put forth by James Hansen before the Select Committee on Energy Independence and Global Warming of the U.S. House of Representatives remains unconfirmed by yet another major study of the subject.

References
Camenisch, M. 2002. Veranderungen der Gipfelflora im Bereich des Schweizerischen Nationalparks: Ein Vergleich uber die letzen 80 Jahre. Jahresber nat forsch Ges Graubunden 111: 27-37.

Grabherr, G, Gottfried, M. and Pauli, H. 1994. Climate effects on mountain plants. Nature 369: 448.

Pauli, H., Gottfried, M. and Grabherr, G. 2001. High summits of the Alps in a changing climate. The oldest observation series on high mountain plant diversity in Europe. In: Walther, G.R., Burga, C.A. and Edwards, P.J. (Eds.) Fingerprints of climate change - Adapted behaviour and shifting species ranges. Kluwer Academic Publisher, New York, New York, USA, pp. 139-149.

Walther, G.R. 2003. Plants in a warmer world. Perspectives in Plant Ecology, Evolution and Systematics 6: 169-185.

Walther G.R., Beissner, S. and Burga, C.A. 2005. Trends in the upward shift of alpine plants. Journal of Vegetation Science 16: 541-548.