From the CO2Science.org archive: Velvet grass, or common velvet grass, is of all things velvety and common. So common that, while imported to North America from Europe as forage, it grew like a weed and is now considered a pest. It has spread across the Northern Hemisphere and into Australia and other Southern Hemisphere settings. Alas it seems to like extra CO2. From 1991 to 2007 there were 11 experiments showing that an additional 300 ppm CO2 boosted velvet grass’ growth by an average of 38.5 percent. If only we could train cows to eat the stuff.