There's lots more information on this available, but this really has nothing to do with OP, because fundamentally OP is not about how many people Earth can feed, but rather what quality of life do we want for those people. Well I read about the new rice which took 10 years to develop and bring into production. I don't know. They sacrifice taste for looks and ship-abality. Nutrition is not calories alone.
Organic gardeners know that the soil matters greatly, and is also rapidly depleted.
We are depleting the world's top soil quickly. We are also depleting the world's oceans. Acid rain is caused mostly by burning minerals like coal which contain some sulfur. This produces Sulfur Dioxide, which later falls to earth as acid rain. More consumption means more energy needs to be produced.