Funny thing about that - I suspect doing either of those would be 10x harder than terraforming Mars. Why? Because there are no Martians to complain about the ecological havoc your changes are making, or to complain that you are depriving them of their livelihood, or possibly destroying culturally significant land forms. I can only imagine the ecological impact reporting that would have to be done in Australia, and I imagine the countries that own the Sahara have their own equivalent.