Megaprojects: Terraforming The Sahara | Answers With Joe
Rather than cover the Sahara with solar panels, why not put a much smaller number on the coast, and use the energy to desalinate sea water and pump it into the desert to allow trees and crops to grow? Maybe even slowly refill Lake Megachad.
As for the Amazon, there's plenty of phosphorus in seawater, so a similar plan might work there too.
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