I agree entirely Ugo, I meant to have a number 4. A much, much more vigorous drive towards viable alternatives is the best option. And that's where energy efficiency comes into its own - enabling activity at a much lower level of energy consumption produced from alternative sources.

How about a number 5. Cut the global population to a level that is sustainable? This would eliminate all of out current energy shortage, water shortage, land-water-air pollution problems?

4. Use our resources to develop renewable energy and/or nuclear, so that we won't need fossil fuels any more.

Hopefully you are proposing following this option in the context of attempting to minimize our current exchange income in terms large scale exchange media like dollars and euros rather than maximizing it (consistent, of course, with the constraint of producing adequate levels of total income). If we do not find a way to substantially decouple the production of pychic income from the consumption of natural resources, then carbon free techno-fixes are not going to get us out of trouble.

If the alternatives to carbon based energy are more expensive than fossil fuels then even the OECD countries may have difficulty producing the constant increases in current exchange income in dollars, euros, etc. that are need for 'healthy' functioning of the financial system, let alone allowing countries like China and India to catch up to us as fast as possible. We need to reduce our total demand on the earth's resources and not just to reduce carbon emissions.