From the CO2Science archive: Percent Dry Weight (Biomass) Increases for Helianthus annuus [Sunflower]. It’s that time of year again (around Ontario at least) when the sunflowers are at their cheery best, all tall and bright and photogenic. And with all that extra CO2 in the air they will continue to brighten our autumns for many years to come. From 1984 to 2017 there were 31 experiments looking at the growth response to an extra 300 ppm CO2, reporting an average increase of 42.5%. 600 ppm yielded an average increase of 31.8%, although that was based on only 4 experiments, and 5 experiments at 900 ppm yielded a growth increase of 70.2%. If the sunflowers this year seem a bit taller and brighter, you can thank your SUV.