I was thinking about this yesterday and came up with this question: How many trees would I have to plant, and how long would they have to live to offset my (average Western European) lifetime CO2 contribution?
I don't recall where, but I recently saw something about the net effect on long-run global temperature being muddled if the tree's dark foliage absorbs more heat than baseline for the environment.
I'm not sure if that's just an asterisk indicating that the short-run effect may be a wash, or if it's clear enough to rule out some environments/tree species in favor of other choices.
Those tree planting drone companies probably require software engineering.