I very much doubt it. Firstly, double from what? 10 ppm to 20 ppm or 50% to 100%? A slight difference you understand. The base temperature is what? Do you get the same results at zero degrees and 200 degrees when doubling CO2? What's the margin of error for the measuring equipment? Is biomass too included in experiments or only gases? When doubling up on co2, what gas is being replaced? Keeping pressures constant?
This claim can be scientifically tested and CO2, focusing on a single molecule, is narrow visioned. The fact is burning hydrocarbons is polluting, plus their products aka plastic. It's also a finite resource. Keep using until alternatives are found, but we should be seeking alternatives.