[selcuka]

Are you sure? There are currently 3 trillion trees on earth and they only absorb about 20% of greenhouse gas emissions (~9.5 GT of CO2) per year [1]. Apparently not all trees absorb the same amount of CO2 as in your assumption. Adding 1 more trillion trees would have a negligible effect.

[1] https://www.pnas.org/doi/10.1073/pnas.1710465114

[somenameforme]

It's not just the absorption as any stroll anywhere near a forest should tell you. They somehow cool areas dramatically, not just through shade, and change local systems substantially. Anyhow, if you want papers, there was one just recently discussed here. [1]

It's expected that planting a trillion trees (amounting to global land coverage of ~8%) which is analogous to pre-industrial times, would reduce overall heating by some 25% (!!) by itself. This also opens the door to yet another not poorly understand feedback system - CO2 increases greenery which increases trees which decreases temperatures far more than previously expected.

[1] - https://news.ycombinator.com/item?id=44221489