You've really got to distinguish between different types of agriculture when discussing efficiency, and specify the metrics you are optimizing for. Row crops/g

You've really got to distinguish between different types of agriculture when discussing efficiency, and specify the metrics you are optimizing for. Row crops/grains, fruits, vegetables, and meat all have different growing conditions, footprints, and shipping concerns. A tonne of wheat costs 0.05 tonnes of CO2 to ship from Kansas to New York, requires 0.6 acres to grow, and contains ~3,500,000 calories. A tonne of tomatoes costs 0.3 tonnes of CO2 to ship from California to New York, requires 0.06 acres to grow, and contains ~180,000 calories. The lowest-hanging fruit, so to speak, in food production is reducing beef production to pasture-raised beef on lands that can be sustainably ranched but are not suitable for other forms of agriculture. After that comes producing more (of some types of) vegetables locally, particularly ones that are mostly water and consumed for nutrients rather than calories, and eating fresh foods in-season. Any plan that tries to get rid of grains or other staples produced on massive scales in monoculture fields in the parts of countries best suited for them runs afoul of the "we need to produce enough food for 10 billion people for at least the next two centuries" constraint of agricultural planning.