Ask HN: Is genetically modified trees to capture CO2 possible?

Probably be better to grow Wolffia (or duckweed) in vats. Under optimal conditions they can double in size daily, and they are human and livestock edible and can be composted to convert into fertilizer or they could be sterilized and used to feed fish or serve as a food source for lake or ocean farming.

Further, they seem to grow best in slightly acidic highly carbonized water, so you could extract CO2 from the air (by refrigerating the air into a liquid) and dump it into the Wolffia vats for them to convert into plant material.

Worst case, you could burn the Wolffia for nearly direct conversion of CO2 into raw carbon to be buried in old abandoned mines and such.

The problem is that currently growing Wolffia is difficult, and scaling that up to meet the needs of the near future would be an inordinate task, but if someone is up to it then godspeed.