USFS studies, and US data on overall arable land. I broke it out in a prior thread exhaustively, but it’s been covered in other areas too. Here is one [https://www.nrs.fs.usda.gov/pubs/gtr/gtr_wo059.pdf]
The US emits a truly massive amount of fossil carbon. [https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emis...], “Total emissions in 2022 are 6,343.2 Million Metric Tons of CO₂ equivalent”. Yes, that is 6 billion metric tons of co2 equivalent a year. 6 trillion kg. Or about 20,000 kg per person in the US, every year.
Currently (since ~ 1990), US forested land is estimated to offset ~ 13% of fossil co2 emissions. Forests cover 36% (!) of US land area, and have been slowly increasing since ~ 2000.
Pretty much all the rest is either 1) waterways, 2) cities, 3) non-arable land like steep mountains and deserts with no ready source of water.
So even with a back of the envelope, easy math, if we changed all our farmland to grow forests, we’d roughly double the amount of carbon we could sequester - which would still be ~ 25% of the amount of fossil carbon we’re emitting, every year.
And then we would still need to DO something with all that wood, because burning it or letting it rot just releases all it’s co2 back into the atmosphere.
