Breaking: CO2 helps plants grow, and some of those are species we don't like

Weeds From Hell in a Greenhouse World | OnEarth Magazine

The problem in this case isn’t related to the global warming that CO2 is helping to cause, but rather has to do with how the gas affects the weed's growth. Carbon dioxide acts as sort of fertilizer, making yellow starthistle grow like… well, it’s already a weed, so perhaps a "super-weed" is the right term.
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"The take home message," he says, "is that there are a bunch of species that are going to benefit in the future, and there’s reason to believe that in many cases they're the species we don’t like. Poison ivy benefits immensely from increased CO2; it’s more competitive, and it produces worse toxins." His research, along with other studies, "suggests that our costs for managing the landscape to be the way we like it are going to go up."