Green hybrids?

I was recently exposed to a tv ad for a car that was so fuel-efficient that it made leaves go flying back onto trees, making the trees green again. That was nice, but I started thinking: "How does fuel-efficiency help the trees? By reducing emissions, right? Emissions like carbon dioxide? Didn't I learn back in elementary school that the ol' exhale stuff is good for trees? Did science reverse itself (yet again) and decide that CO2 actually hurts trees? How did I not hear about that? That ranks right up there with Pluto not being a planet, as newsworthy scientific discoveries go. It must be an oil company conspiracy that silenced those brave scientists who made that discovery.

SRS