What was done
Because "heat hardening" of leaf tissue can occur within hours or even minutes when critical high-temperature thresholds are surpassed (Alexandrov, 1977), the authors used solar-powered portable field heat tolerance test equipment described by Buchner and Neuner (2001) to monitor the variability of heat tolerance in a number of alpine plants, including herbaceous and rosette plants, cushions, dwarf shrubs and shrubs, throughout diurnal cycles, seasonal cycles, and in a controlled in situ heat treatment (+3°C) provided by infrared lamps throughout two seasons (1998, 1999) at three sites at a minimum of weekly intervals, obtaining more than 4000 individual measurements of heat tolerance and simultaneous recordings of microclimate parameters.

What was learned
Buchner and Neuner report that "heat tolerance increased under warmer microsite conditions and in warmer years," while "long-term artificial heating by +3°C led to a significant (P less than 0.01) increase in heat tolerance by +0.6°C."  In their diurnal studies, heat tolerance changes greater than 1.5°C occurred on 18% of summer days at a velocity of 0.4-2.2°C per hour, with an amplitude ranging from 4.8 to 9.5°C.  Of particular interest was the observation that in the summer of 1998, which was significantly warmer than the colder summer of 1999, the heat tolerance of most of the plants was also significantly higher.  In addition, they report that "the higher the mean maximum leaf temperatures at a particular growing site, the higher the mean heat tolerance in leaves."

What it means
The University of Innsbruck scientists say that because "the year 1998 has been one of the warmest years in the Northern Hemisphere since the beginning of systematic worldwide climate registrations ? that year may thus serve as a good indication of the potential response to global warming."  In this regard, they note that "under the warmer conditions of 1998, all species investigated had a higher heat tolerance and showed sufficient heat hardening to overcome high temperatures."  To this observation we would add that any future concomitant increase in atmospheric CO2 concentration would likely also enhance earth's plants' abilities to survive higher maximum temperatures (Taub et al., 2000).  Consequently, earth's vegetation may be far less threatened by rising temperatures than what climate alarmists typically claim.  See also, in this regard, our major report The Specter of Species Extinction: Will Global Warming Decimate Earth's Biosphere?

Reference
Alexandrov, V.Y.  1977.  Cells, Molecules and Temperature.  Springer, Berlin, Germany.

Buchner, O. and Neuner, G.  2001.  Determination of heat tolerance: a new equipment for field measurements.  Journal of Applied Botany 75: 130-137.

Taub, D.R., Seeman, J.R. and Coleman, J.S.  2000.  Growth in elevated CO2 protects photosynthesis against high-temperature damage.  Plant, Cell and Environment 23: 649-656.