Well......
Plant a trillion trees. So that's about 143 trees per person on the planet.
Still. It's supposedly possible, the space is available and according to a study it could reduce CO2 levels substantially
A way to fight climate change? Plant a trillion trees - The Boston Globe (https://www.bostonglobe.com/news/nation/2019/07/04/way-fight-climate-change-plant-trillion-trees/G4ujnMxBjJtSjRYWDyx8YM/story.html?outputType=amp&__twitter_impression=true)
Have a read and see what you think.