Global warming is reversible - but not with current patterns of land and energy use. It will take *more* than 15 years to confirm that global warming is occuring but that is not a reason to avoid action now. Solar energy will be *more* viable if we invest money in it. But it will never provide the same amount of energy as fossil fuels. That may not matter if we use energy more efficiently than we do now. That is where I believe our efforts should be concentrated - energy efficiency. Nuclear energy will be viable (including politically viable) if/when 'the oil runs out'. In any case - define 'viable'. New technology, economies of scale, better efficiency and supply/demand issues can rapidly change the unviable to the viable. As for previous changes in power sources. It is virtually impossible to learn from the past in this situation because we have never had a problem like this before. In any case, those previous changes were often unexpected. One day all of a sudden civilisation gave us iron, coal, trains, electricity, radio, internal combustion engines, rockets, computers. Nobody....NOBODY....knows what will be next. How on Earth can anyone know what will be viable in 5, 10 or 20 years time? References: Precautionary Principle Post-normal Science Monte. ok it may take 15 years but considering we know it has happend, and the possible effects of our emmisions its surly best to do somthing now before the "possible" damage becomes proven and also irrivercable. Also using less fossil fules will save oil reservs for use in plastics because when oil runs out plastics such as ployethane (more commly called polothene) cannot be made, the we will have alot of problems.