Trees are not as effective as grasslands for carbon sequestration.

https://phys.org/news/2018-07-grasslands-reliable-carbon-tre...

Regardless, Ag can never be part of a carbon negative initiative. I am curious as to how this will go..

A trillion tons of anything has a LOT of volume. Even assuming that we could somehow convert/compress a trillion tons of CO2 to 10 times the density of water (that is denser than solid iron would be) it would still take up 100,000,000,000 cubic metres = 100 cubic kilometres = 24 cubic miles = quite a sizable mountain