I'll bite, though I probably shouldn't. The problem with *trees* cleaning up the CO2 is that you'd have to bury them when they died to sequester the CO2. Otherwise, as the tree rots, or is burned, or whatever...the CO2 is going to release straight back into the atmosphere.
jcotton writes "Here's your chance to name something much bigger than a street after yourself. TierneyLab hereby promises to name Saturn's mysterious hexagon after the reader who comes up with the most entertaining explanation for this 15,000-mile wide feature at the planet's north pole. NASA says it looks like clouds are whipping around. The New York Times, science times and space.com all report."