On a related note, here is a discussion about how many trees it would take to solve climate change: https://earthscience.stackexchange.com/questions/2639/how-ma...
The number of trees needed (1.2T) is pretty close to the estimation of the accepted answer in your link (1.5T). The difference is, the up-to-date study has found that there is enough space for the trees. Now we just need to plant them :)