Here's my problem with this. I did a calculation for how many trees I'd need to plant in order to remove the CO2 produced on a flight from Grand Rapids, MI to Baltimore. The site says I'd need to plany one tree (at a cost of $11 and change, which they can conveiniently collect right now since I asked). I'm pretty sure a tree isn't going to clean up the 600+ pounds of CO2 produced by that flight in, say, the same time it took to produce that CO2. So really, to have a zero sum, I'd need to plant something on the lines of acres of trees.
Michigan State University's Center for Integrative Toxicology, says this:
It is estimated that an acre of trees uses four and a half tons of CO2 a year
Doing some real quick math, that's about 25 pounds a day per acre.
Something smells funny...