planting trees to offset cars CO2

I thought it would be a cool idea to encourage/require people to plant trees to offset the CO2 that any car they buy would put out.
Here’s an article about the overall concept: http://en.wikipedia.org/wiki/Carbon_offset

So when you buy a new car, you pay into a fund for planting the trees. Here’s a program that does this:http://treesftf.org/about/cooling.htm
Also a local electric auto company has a similar program: http://zaptrees.org/ourmission.htm

Anyway I wanted to find out how many trees would offset the CO2 output of a car. In round numbers it is 200 trees.
A car with average mileage and average MPG puts out about 10000 pounds of CO2 per year.
A tree absorbs about 50 pounds of CO2 per year (Carbon Sequestration http://en.wikipedia.org/wiki/Carbon_sequestration)
These are very rough numbers, there are lots of issues, like what species of tree, where it is planted, etc.

To find out how much CO2 you put out, see the Personal CO2 emissions calculator:
http://www.epa.gov/climatechange/emissions/ind_calculator.html