Reference
Pauli, H., Gottfried, M., Dullinger, S., Abdaladze, O., Akhalkatsi, M., Alonso, J.L.B., Coldea, G., Dick, J., Erschbamer, B., Calzado, R.F., Ghosn, D., Holten, J.I., Kanka, R. Kazakis, G., Kollar, J., Larsson, P., Moiseev, P., Moiseev, D., Molau, U., Mesa, J.M., Nagy, L., Pelino, G., Pusca, M., Rssi, G., Stanisci, A., Syverhuset, A.O., Theurillat, J.-P., Tomaselli, M., Unterluggauer, P., Villar, L., Vittoz, P. and Grabherr, G. 2010. Recent plant diversity changes on Europe's mountain summits. Science 336: 353-355.
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" (i.e., driven to extinction) in response to global warming that encourages the upward migration of plants on mountains. But is this really the case?
What was done
As part of a massive program designed to address this and other related questions, a team of 32 researchers documented plant species occurrences on 66 mountain summits distributed across 17 study regions that included all major mountain systems of Europe in 2001 and again in 2008, over which intervening period the climates of the studied regions are known to have warmed. And in the 20 April 2012 issue of Science, they report their findings.
What was learned
Pauli et al. found that the number of all species recorded across all 66 summits increased from 821 to 869 (~6%) over their study period, while the number of endemic species (i.e., those that were long-time residents of the mountain tops) rose from 201 to 203 (~1%). And this was the case, even though the availability of water in some of the regions significantly declined over the study period.
What it means
Although mountaintop warming throughout all of Europe between 2001 and 2008 did indeed lead to upward migrations of several plant species, those at the tops of the mountains were not "pushed off the planet."