What will happen when the gas runs out, when the deepest oil well of the Arabian peninsula finally runs dry, when the giant drills of the offshore platforms reach nothing but dry rock? Will we face a future of blackouts and electricity rationing, or will we find a way to avert the doomiest scenarios and continue living lives in which energy consumption is crucial to everything we do.
Think of the electricity you use in a day. You are woken by the clock radio buzzing into life, and you turn the bathroom light on as you climb into your power shower. After dressing you head downstairs, where you turn on another radio, put some bread into the toaster and turn on the kettle, getting the milk from your fridge to put in your tea. After breakfast you head to work, where the lights are burning - and on go the computer and desktop fan.
Those are just the most obvious of personal uses and the day has barely even begun. How can we possibly sustain such a level of usage? In short: renewable energy sources.
There is no longer any doubt that renewable energies will play a large part in the future of mankind. If politicians show sufficient will and intelligence, and invest in a raft of new technologies, then we should be able to maintain our electricity supply and, as a beneficial side-effect, avert the disaster of rapid global warming.
But as with the debate about nuclear power in the 1980s, it will not be environmental arguments that win the day, but economics.
Nuclear power lost out not because of the vexed question of radioactive waste but because the truth finally emerged that it was a very expensive way to keep the lights on.
When oil and natural gas begin to run out - and, more importantly, when demand exceeds supply - their prices will escalate and the cost of using them to generate electricity will become prohibitive. Continuing to use coal or, worse, increasing the quantity we burn will be more and more unacceptable, because it will add to the excessive quantities of carbon dioxide in the atmosphere. Those factors make both renewables and nuclear more and more competitive.
The renewables revolution has begun already, because researchers are anticipating the moment when renewables become economic. Although there are a range of renewables already in use, the contribution to world energy production - hydropower aside - remains relatively minor, at less than 1%. But there is a large selection of new renewables under research and development.
Hydropower is already one of the largest and most established forms of renewable energy, providing 19% of the world's electricity. Of the others, geothermal is a long established and growing energy resource, and wind power is already a mainstream technology. A variety of other smaller technologies are also already economic, the best of which involves using methane from landfill sites. Across the world a mixture of other fuels from specially grown trees, forest offcuts, pig slurry, straw and even chicken litter are generating power. And there are others that are, as yet, underexploited but with great potential: solar is growing fast, and tidal, ocean currents and wave power are also undergoing rapid development. Further ahead, though not before 2020, lots of other possibilities exist - the prospect of the hydrogen economy and completely clean energy production has led to much excited speculation.
In Europe, money is being poured into wave and tidal power. Undersea turbines, working on much the same principle as wind turbines, are already in operation in the UK and Norway. Their potential is huge, particularly because all along the Atlantic coast with its large tides, and many inlets and islands, there are countless sites for exploiting the power of the sea. And unlike the winds, tides are completely predictable.
Wave power has great potential in exactly the same areas, and although the technical difficulties already encountered in its development means it has been expensive, there are many companies confident they can make it work.
There is a race among developed countries to become leaders in these new technologies because of their vast potential to create jobs and exports.
Geothermal technology is increasing in regional importance, particularly in countries that do not have a wind, tidal or wave resource. This heat is as inexhaustible and renewable as solar energy and comes from hot rocks near the earth's surface. Water is pumped into the hot ground and used on its return to the surface to create electricity and for district heating. The main geothermal areas of this type are located in New Zealand, Japan, Indonesia, Philippines, the western coastal Americas, the central and eastern parts of the Mediterranean, Iceland, the Azores and eastern Africa.
But while all that sounds very exciting, leading environmental groups and engineers to take on the challenges of developing energy technology, mainstream organisations such as the World Energy Council still see fossil fuels dominating the agenda in 2020. That is mainly because the worldwide demand for electricity is escalating so fast they cannot see renewables catching up with the demand. The council is first to admit it could be wrong. It all depends on how quickly the oil and gas begin to run out.
And then there is the nuclear question. It is not only the renewable industry that sees opportunities in the coming energy crisis and in our fears about the devastating effects of global warming. The nuclear industry rightly claims it provides a reliable source of energy that does not produce the carbon dioxide that fossil fuels do. But nuclear power is still dogged by the old, familiar problems: it takes a long time to take a nuclear power station from the drawing board to production; nor has anyone yet come up with a satisfactory method of disposing of nuclear waste. Neither of those disadvantages are attached to the new renewables.
Currently there are 444 nuclear reactors worldwide, producing 16% of the world's electricity. Some countries rely on nuclear power for most of their electricity. France is the top of the list, generating 75% of its electricity in nuclear power stations. But most of the countries that have a lot of reactors - particularly in North America and Europe, with Japan also on the list - have stopped building new ones or have curtailed their programmes. As a result the closure programme is exceeding the rate of new building.
But that does not mean there will be no nuclear revival. The nuclear industry is looking to expand into the growing economies of Asia, particularly in China, South Korea and India. China has just ordered four new stations and may confirm another four before Christmas. There are said to be plans to build two a year but even that expansion would only account for a tiny part of the massive need for power in that vast and fast-growing economy. Even the fourfold increase in the rate of Chinese nuclear expansion which the industry hopes to see by 2020 would provide less than 20% of the country's power. Other solutions are needed.
The nuclear industry's other hope for a big push is the United States, not only because it is the world's largest economy but also because it is the one most dependent on oil and gas, and the one that wastes most of both. The energy crisis, when it comes, is going to hit first, and worst, the US. It is from there that the political push to make the world change course may come.
The current administration does not give the world many reasons to hope. President George Bush was the man who repudiated the Kyoto protocol, which was designed to reduce greenhouse gases. Kyoto was one of the drivers of the renewable revolution and the fact that it has stalled because of the objections of the US and indecision of Russia has slowed progress towards their greater use.
Despite his links to the oil industry, Dick Cheney, the vice president, pushed hard at the start of Bush's four-year term for a revival of the nuclear dream. So far nothing has happened, partly because of continued public resistance in the US and partly because of the lack of private investment. But the main barrier still remains the large capital cost of building a new nuclear power station. If you forget the costs of the pollution caused by fossil fuels (which is what the US does in its energy planning) then new coal or gas stations are far cheaper.
But part of America's charm is its diversity of view. In August, California announced a plan to subsidise solar power for one million homes by surcharging consumers about 15 pence a month. The state aims to rival Japan and Germany in being a world leader in solar power.
This debate about whether nuclear power is a viable energy source for the future has also started to grip Europe. Despite the heat being generated in the debate, expansion does not seem a viable option, mainly because of public resistance. Instead, many of the countries of western Europe have invested heavily in wind power, particularly Portugal, Spain, France, Denmark and Germany.
In the UK, where nuclear stations are closing on a regular basis as they reach the end of their lives, about 20% of electricity still comes from reactors. However, there would be serious obstacles to building a new station, as a minority demands. It is estimated it would be 2020 before a new station could be finished, even if planning began now. By that time wind power will be producing about 15% of the UK's power, replacing the lost nuclear production.
The opponents of the nuclear option say the future lies in the new breed of renewables, the potential of which is only now being fully understood. Although there is still room for more hydropower, it is the new technologies that hold out most hope.
The new generation of energy, then, is likely to lie with forces as old as the earth itself: the elemental powers of the wind, waves and sun. The very things that have shaped so much of our past will also, with the application of the human factor of technology, help shape our future.