What was done
Among a number of other things, the authors explored the concurrent effects of elevated atmospheric CO2 concentration and temperature on photosynthetic CO2 fixation in cotton (Gossypium hirsutum L. cv. Coker 100A-glandless), using "intact plants and biochemical measurements to directly determine how environmental change impacts specific physiological mechanisms important to plant productivity."

What was learned
Over a four-day period of intensive experimentation, Crafts-Brandner and Salvucci observed that "net photosynthesis of cotton leaves at ambient levels of CO2 was inhibited at leaf temperatures above about 32°C."  At a leaf internal CO2 concentration 4.3 times greater than ambient, however, net photosynthesis did not begin to decline until leaf temperatures rose above 40°C.  Viewed another way, the net photosynthetic rate of cotton leaves exposed to ambient air declined by approximately 77% as leaf temperature rose from 32 to 40°C, while that of leaves exposed to the CO2-enriched air actually rose by about 9%, indicating that the increase in atmospheric CO2 concentration more than compensated for the dramatic decrease in photosynthetic rate that would have occurred in its absence in response to the 8°C increase in temperature.

What it means
The ongoing rise in the air's CO2 content would appear to have the capacity to totally thwart the adverse growth effects of any increase in air temperature it might possibly be causing, as we describe in detail in our major report The Specter of Species Extinction: Will Global Warming Decimate Earth's Biosphere?.