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