there are probably better implementations for solar https://www.youtube.com/watch?v=H901KdXgHs4
I would think the tree idea is the way to go but I wonder how many trees per car it would take for neutrality. The problem is that developing nations will be pissy if we tell them they can't do what "westernized" have done to "modernize" unless an economically feasible alternative is developed/provided.
I'm not sure what the tree to car ratio is either but if you have a yard and it is not a challenge to throw a baseball with your son or daughter then it needs more trees. :)