Is there potential to afforest any of the world’s 11bn acres of arid and semi-arid lands, by desalinating and distributing seawater? Energy economics do not work in the most extreme deserts (e.g., the Sahara). Buy $60-120/ton CO2 prices may suffice in semi-arid climates. The best economics of all use waste water from oil and gas, such as in the Permian basin.