Commercial greenhouse operators raise CO2 levels to 1200 ppm, three times atmospheric levels. (drtimball.com)
Commercial greenhouse operators recognize this when they artificially increase the concentrations inside their greenhouses to over 1000 ppm. (firstthings.com)
Schmitt and Happer say our current CO2 levels are «low by the standards of geological and plant evolutionary history,» they pine for the days when «Levels were 3,000 ppm, or more,» and note that commercial greenhouse operators boost CO2 levels to» 1,000 ppm or more to improve the growth and quality of their plants.» (treehugger.com)