What was done
Noting that "the size and growth rate of a seedling is critical for its competitiveness and survival," the authors studied the developmental history of well watered and fertilized sunflower (Helianthus annuus L., cv. Sanluca) plants for the first 15 days after their initial imbibition of water while growing in pots of washed quartz sand in growth chambers maintained at atmospheric CO2 concentrations of either 200 or 1000 ppm.

What was learned
As soon as the cotyledons started to rapidly expand at 4 DAI (days after imbibition), the expansion rate in the CO2-enriched air was about 20% faster than that in the CO2-reduced air; and from that point in time, Lehmeier et al. report that "seedling growth was near exponential, with a 2-2.5 times higher rate at elevated CO2," due largely to an increased unit leaf rate of net carbon assimilation (+120%) and an increased rate of leaf expansion (+60%). By the end of the experiment at 15 DAI, these phenomena had resulted in a 2.5-fold increase in seedling biomass in the CO2-enriched air compared to the CO2-reduced air.

What it means
Getting off to a good start in life applies to plants as well as people; and elevated CO2 appears to help sunflower plants considerably in this regard. If it does the same for other plants, and knowing that the health and well-being of plants is essential to the health and well-being of all higher organisms, one could say that elevated CO2 helps people in this regard too.