If there is just one thing you want to do, and you still want to have done the best you could ever have done for the health of this planet: stop breeding.
All details see vhemt.org , and a study from July 2017 pointing to the impact each new-born will have (considering CO2 emissions only).
Oh and think first before you object that Asia and Africa should stop breeding first, if you happen to sit on a fluffy couch in the "first world". Your unborn child would have wreaked much more havoc on this planet than the average, less pampered homo sapiens.