Keith, There will likely be a race between fossil fuel depletion and the successful deployment of the sustainable energy technologies you describe. Some professionals in the business believe that we are in the last decade of increasing flows of fossil fuel; (Hubbert Peak). After that, no amount of drilling, mining...will produce greater flows. Also, oil will be used for chemical purposes even when alt energies come on stream. Best guess is coal replacing oil & gas as energy source for a few decades. They better clean up the power plant technology, and fast.
A secondary constraint is fresh, clean water. With ample energy, desalinisation and purification are possible. Waste sink overload is third. It entails atmospheric as well as ground water & soil toxification. Nanotech & the like may help; it's too soon to tell. Steve -- http://magma.ca/~gpco/ http://www.scientists4pr.org/ Anyone who believes exponential growth can go on forever in a finite world is either a madman or an economist.--Kenneth Boulding
