This must be the most counter-factual article I have ever read

The opening assumptions are wrong: Greater warmth PROMOTES plant growth (as anybody who has visited the tropics knows) and warmer seas should produce MORE evaporation/rain (and hence more soil moisture). And the innovative aspect of the article -- causing an unenclosed space to preserve an unusually high concentration of CO2 -- sounds a very approximate and hard-to-control procedure, given the speed of gaseous diffusion etc. Talk about false premises! Editorial summary given below followed by the journal abstract. The article is of course from the now sadly misnamed "Science" magazine. The findings can only have been arrived at via one of those famous "models", which will give you any result you want -- dependant only on the assumptions plugged in. And you can be assured that the assumptions were very "Green"

Plant Productivity Benefits of High Carbon Dioxide Busted

Although rising CO2 levels may reduce global crop yields through the effects of higher temperatures and decreased soil moisture, arguments have been made that direct fertilization effects will more than offset these losses. Long et al. (p. 1918; see the Perspective by Schimel) present a critical analysis of data on which the Intergovernmental Panel for Climate Change base their projections that elevated CO2 will have a fertilizing effect. The original estimates came from experiments conducted in the 1980s in greenhouses and sheltered enclosures. More sobering figures are derived from open-field studies in which increased CO2 levels enhanced crop yields ~50% less than in enclosure studies.

Food for Thought: Lower-Than-Expected Crop Yield Stimulation with Rising CO2 Concentrations

Stephen P. Long et al.

Model projections suggest that although increased temperature and decreased soil moisture will act to reduce global crop yields by 2050, the direct fertilization effect of rising carbon dioxide concentration ([CO2]) will offset these losses. The CO2 fertilization factors used in models to project future yields were derived from enclosure studies conducted approximately 20 years ago. Free-air concentration enrichment (FACE) technology has now facilitated large-scale trials of the major grain crops at elevated [CO2] under fully open-air field conditions. In those trials, elevated [CO2] enhanced yield by 50% less than in enclosure studies. This casts serious doubt on projections that rising [CO2] will fully offset losses due to climate change.

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