If you want to suck up some co2 then detonate a few nukes near...

If you want to suck up some co2 then detonate a few nukes near the coast when the prevailing wind is toward the ocean. The phytoplankton bloom would be far greater than anything you could achieve with a timber plantation. Then there are eco friendly building materials that absorb co2.

As you correctly pointed out, agriculture, like any enterprise, should turn a profit to justify itself.

Billy