Alzo, today we seem no closer to realising the dream of unlimited supplies of energy from nuclear fusion than we were thirty years ago. According to one scientist, who has worked on nuclear fusion, the nail in the coffin of nuclear fusion will prove to be the lack of sufficient supplies of the necessary hydrogen isotope tritium. For further information, see the forthcoming second edition of "The Final Energy Crisis" edited by Sheila Newman (http://candobetter.org/sheila).
Hazards of nuclear fission
In regard to nuclear fission, it is obviously a more viable source of energy that just may, if we are extremely careful, provide a bridge towards a more sustainable future whilst stocks of Uranium and Thorium last, however it has a very considerable environmental cost. If we increase the scale of nuclear power generation to the extent necessary to fill the gap power the environmental risks we currently face will be multiplied many times. The Chernobyl disaster. which could have been far worst if not for the quick thinking of those courageous workers on the spot is one illustration. On top of the hazards of nuclear fission electricity generation, even more environmental threats are posed by mining of uranium, enrichment, reprocessing and disposal of nuclear wastes. A likely consequence of the expansion of uranium mining in Central Australia is that the Eastern seaboard stands to be exposed to clouds bearing poisonous radioactive uranium and other toxic metals blown from the mine tailings dumps (see David Bradbury's film "Blowin' in the wind" for a graphic illustration of this threat). In the past, the long-term containment of tailings from mining operation has been problematic and, more often than not, fails in the longer term (as Jared Diamond has illustrated in describing past mining operations in Montana in Chapter 2 of "Collapse" pp35-41). I don't hold out any greater hope that the mining companies will do any better a job containing the mountains of tailings from the planned expanded Uranium mines.
Practical limitations of nuclear fission
Another problem with nuclear fission is that it can only be used to generate electricity. In order to operate transport or run factory machinery or mine milling equipment, the electricity has to be either somehow stored chemically, or transported directly as electricity using power lines, transformers and other expensive infrastructure. In the former case, energy is lost, in creating, for example, hydrogen from water, and the containment of hydrogen necessitates the fabrication of particularly strong and well-sealed containers. In the latter case, large quantities of non-renewable resources, particularly copper, are required, and it is expected that the world's production of copper will begin to decline next year (http://www.sciam.com/article.cfm?chanID=sa003&articleID=000CEA15-3272-13C8-9BFE83414B7FFE87).
Practical limitations of other 'renewables'
The other "lots of possible energy sources" are essentially derived from solar energy or geothermal energy. All require the use of equipment, the manufacture of which now requires non-renewable rare metals, petroleum-derived plastics and fossil fuel energy. The problems in building renewable energy generators, on a scale necessary to indefinitely meet global society's demands, as well as to provide the necessary additional energy to build replacement generators and infrastructure, without reliance upon fossil-fuel energy, appear to be overwhelming. It seems unlikely that this can be done on a scale anywhere near the scale we have been able to do thus far relying on our finite endowment of fossil fuels.
Applying the precautionary principle
So, I would suggest that it would be extremely imprudent to continue to consume natural resources at our current rate, let alone to increase our rate of consumption, and to go on trashing the world's ecology as we are doing now on the assumption that we can find an easy replacement to so much of that conveniently packaged solar energy captured over tens of millions of years that we have found buried under the ground. It would be far more prudent to assume that our current practices are unsustainable, and to begin now to reduce those levels of consumption.
Those who are consuming the most whilst contributing the least to society, such as property speculators and financial advisers should be amongst the first to be made to do so.