Background
Various researchers, such as Gonzalo-Turpin and Hazard (2009), have periodically stated that alpine ecosystems are "threatened by global warming" and that the many species that comprise them "are at risk of extinction," while NASA's James Hansen, whose language is a bit more dramatic, has stated that life in alpine regions is in danger of being "pushed off the planet" by rising temperatures, as it has "no place else to go." So are these claims correct?

What was done
Working within the Swiss Alps, Stocklin et al. studied the consequences of the highly structured alpine landscape for evolutionary processes in four different plants (Epilobium fleischeri, Geum reptans, Campanula thyrsoides and Poa alpina), testing for whether genetic diversity within their populations was related to altitude and land use, while seeking to determine whether genetic differentiation among populations was more related to different land use or to geographic distances.

What was learned
The three Swiss scientists determined that within-population genetic diversity of the four species was high and mostly not related to altitude and population size, while finding that genetic differentiation among populations was pronounced and strongly increasing with distance, implying "considerable genetic drift among populations of alpine plants."

What it means
Based on their findings, as well as the observations of others, Stocklin et al. note that "phenotypic plasticity is particularly pronounced in alpine plants," and that "because of the high heterogeneity of the alpine landscape, the pronounced capacity of a single genotype to exhibit variable phenotypes is a clear advantage for the persistence and survival of alpine plants." Hence, they conclude that "the evolutionary potential to respond to global change is mostly intact in alpine plants, even at high altitude."

This result makes it much easier to understand why -- even in the face of significant 20th-century global warming -- there have been no species of plants that have been observed to have been pushed off the planet in alpine regions, as has been demonstrated to be the case by a number of pertinent studies, including those of Walther et al. (2005), Kullman (2007), Holzinger et al. (2008), Randin et al. (2009), and Erschbamer et al. (2009).

References
Erschbamer, B., Kiebacher, T., Mallaun, M. and Unterluggauer, P. 2009. Short-term signals of climate change along an altitudinal gradient in the South Alps. Plant Ecology 202: 79-89.

Gonzalo-Turpin, H. and Hazard, L. 2009. Local adaptation occurs along altitudinal gradient despite the existence of gene flow in the alpine plant species Festuca eskia. Journal of Ecology 97: 742-751.

Holzinger, B., Hulber, K., Camenisch, M. and Grabherr, G. 2008. Changes in plant species richness over the last century in the eastern Swiss Alps: elevational gradient, bedrock effects and migration rates. Plant Ecology 195: 179-196.

Kullman, L. 2007. Long-term geobotanical observations of climate change impacts in the Scandes of West-Central Sweden. Nordic Journal of Botany 24: 445-467.

Randin, C.F., Engler, R., Normand, S., Zappa, M., Zimmermann, N.E., Pearman, P.B., Vittoz, P., Thuiller, W. and Guisan, A. 2009. Climate change and plant distribution: local models predict high-elevation persistence. Global Change Biology 15: 1557-1569.

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.