“All solutions presented in Drawdown are not just hypothetical. They are real, well-understood technologies and processes that can be scaled around the world. The breakthrough research required for the book has resulted in dozens of new scientific papers, and there are 20 more solutions coming that could create an even greater reduction in greenhouse gases.”

http://www.drawdown.org/

Below are the top 10 solutions in order of greatest impact (as of 2018)

(…further solutions, summarized by rank)