Look here for an excellent and exhaustive appraisal of our global energy future.
The link goes to a lecture by California Institute of Technology Professor Nathan S. Lewis, who tallies current energy usage, likely world energy reserves and future demand, based on likely population growth. You can download a 16-page text, complete with a PowerPoint or you can stream an audio feed of the whole nearly hour-long lecture.
Or you can read on for some highlights.
Prof. Lewis has calculated, perhaps alarmingly, that we have ample fossil fuel reserves to continue spewing CO2 into the atmosphere for somewhere between 200 and 2,000 years. More specifically, he says:
"We need to consider both the estimated total reserves (i.e. quantities of fossil energy with 90% confidence that such supplies exist), from both conventional and unconventional sources, and the estimated resource base of the various fossil fuels: oil, gas, and coal. From simple arithmetic of dividing the total reserve and/or resource base by the current burn rate of each type of fossil energy, it can be seen that we have between 40 and 80 years worth of oil reserves globally at our current burn rate of oil, and we have between 50-150 years of oil if the resource base is included. We have between 200-500 years of reserves of natural gas, and between 207-590 years of gas reserves, not including the natural gas potentially available as methane clathrates in the continental shelves. Similarly, we have between 200-2000 years of coal.
"The conclusions of this calculation are that we have an abundant, relatively inexpensive global resource base of fossil fuels. There are, of course, different geopolitical and regional factors that are certainly going to come into play (and which have historically done so) that will affect pricing of energy, but globally, we have an abundant inexpensive resource base of fossil fuels that will last us for hundreds of years, if we choose to exploit it. Furthermore, at some additional cost, one type of fossil fuel can be convereted into another, so that a limited global supply of one fossil energy resource (for example, oil) could be compensated for in principle by additional consumption of another fossil fuel (for example, coal). And so one can conclude that renewables will not play a large role in primary power generation unless or until some technological breakthrough is achieved, or unless/until some unpriced externality becomes introduced into energy pricing. This is a controversial conclusion to some audiences, but I believe that the numbers presented herein support the conclusion analytically."
One "unpriced externality" could be a climate change crisis of sufficient proportions to bring humankind to its senses.
Lewis goes on to canvass no-carbon energy alternatives (including carbon sequestration measures), but he begins here:
"One option that ... must be included prominently in any discussion of carbon-free power, is nuclear power, either from fission or possibly in the future from fusion. Currently about 400 nuclear power plants exist globally. The IPCC projections included an expansion of nuclear power in arriving at the quoted energy mix overall. However, it is possible to consider a much larger contribution of nuclear power to address the carbon-free power need. Nuclear power plants typically do not scale well because of heat dissipation, and their size is now about 1 GW. To produce 10 TW of power would require construction of 10,000 new nuclear power plants over the next 50 years, i.e., one every other day somewhere in the world for the next 50 years. I will leave the reader to decide whether or not that is a viable option, but it is technically possible in principle as an approach to obtain the required level of carbon-free power."
It gives you some sense of the scope of the challenge that lies before us. And regardless, the entire lecture is well worth the read.