Background
The CO2-induced global warming extinction hypothesis claims that as the world warms in response to the ongoing rise in the air's CO2 content, many species of plants and animals will not be able to migrate either poleward in latitude or upward in elevation fast enough to avoid extinction, as they strive to escape various debilitating stresses imposed by rising temperatures.

What was done
The authors investigated this climate-alarmist contention by resurveying (in July/August 2003) the floristic composition of the uppermost ten meters of ten mountain summits in the Swiss Alps, applying the same methodology used in earlier surveys of the same mountain tops by Rubel (1912), which was conducted in 1905, and Hofer (1992), which was conducted in 1985. Hence, their analysis covered the bulk of the Little Ice Age-to-Current Warm Period transition (1905-2003), the last portion of which (1985-2003) is claimed by climate alarmists to have experienced a warming that was unprecedented over the past two millennia in terms of both the rate of temperature rise and the level to which the temperature rose.

What was learned
Whereas the mean increase in species numbers recorded by Hofer (1992) for the time interval 1905 to 1985 was 86%, Walther et al. report that "species numbers recorded in 2003 were generally more than double (138%) compared to the results by Rubel (1912) and 26% higher than those reported by Hofer (1992)." Put another way, they say "the rate of change in species richness (3.7 species/decade) was significantly greater in the later period compared to the Hofer resurvey (1.3 species/decade)." Most important of all, they say "the observed increase in species numbers does not entail the replacement of high alpine specialists by species from lower altitudes [our italics], but rather has led to an enrichment [our italics] of the overall summit plant diversity."

What it means
In spite of the apparent reasonableness of the global warming extinction hypothesis, whereby high-altitude species are expected to be "squeezed out of existence" by other species migrating upwards from lower mountain levels to escape the stress of increasing temperatures, Walther et al. find no sign of this dire consequence over an entire century of warming in the Swiss Alps, in harmony with the similar findings of other researchers that we describe in more detail in our major report The Specter of Species Extinction: Will Global Warming Decimate Earth's Biosphere?

References
Hofer, H.R. 1992. Veranderungen in der Vegetation von 14 Gipfeln des Berninagebietes zwischen 1905 und 1985. Ber. Geobot. Inst. Eidgenoss. Tech. Hochsch. Stift. Rubel Zur 58: 39-54.

Rubel, E. 1912. Pflanzengeographische Monographie des Berninagebietes. Engelmann, Leipzig, DE.