Since readers have been the unwitting passengers (or guinea-pigs?) on this voyage into the future, it might be helpful to try to set out here what we do know about it: where we can be reasonably confident, and where we really have to acknowledge that we are making judgements that I hope are right, but may turn out to be wrong. The surprising thing is that there are some very important areas, including demography and technology, where we know quite a lot, yet others, such as shifts in political and social attitudes, where we are in the dark.
Start with demography. We know that the 5.5 billion or so people on earth now will have increased to about 8.5 billion by 2020. We know that almost the entire rise will take place in the developing world. And we know that the age structure of developed countries will change so that there will be a much higher proportion of elderly people than there are today. The rich world will be old; the poor world will be young.
Can we feed another 3 billion people? Probably, but the food will tend to be in the wrong place. The farmers of North America and Europe can crank out a lot more food - at the moment they are being paid not to produce it - but the population growth will be mainly in Africa, the Indian sub-continent and China. Land and, more important, water for irrigation are already quite tight, so even assuming a continued rise in crop yields, it will be difficult for these regions to feed themselves. They will have to develop products to export to help to pay for imports of food, and we will have to buy them.
Will there be sufficient other resources, for example energy? Here we can be reasonably confident, for the supply of most natural resources appears adequate for at least one more generation. There will only just be enough oil, but as the price rises substitutes will be developed. Rising energy demand will, however, lead to greater use of fossil fuels which will in turn increase global warming. While we are likely to see only the very early consequences of that by 2020, it will have become a greater concern to the world.
We can predict the technologies that might be in everyday use in a generation because they exist in some form now. It takes the best part of a generation from discovery to popular use: the integrated circuit, which brought both the fax and the computer down to a price and size suitable for home use, was invented as far back as 1958. What is much harder to judge is which technologies will be commercially successful and so enter all our lives. The Boeing 747 and Concorde were developed at the same time: one has revolutionised inter-continental travel; the other is a quirky example of what technology can - and cannot - achieve if enough resources are put into it.
We can already see, to take one extreme example, that housing technology will hardly change. A generation from now we will be living in similar homes to those of today, though they will be equipped with even more electronic gadgetry. Homes are home are homes, and the nicest ones seem to have been built at least 100 years ago. (That is not just a British fad: the most expensive flats in Paris are turn-of-the-century buildings in the 16th arrondissement.)
To move up one stage, electro-mechanical technology will continue its incremental advance - but change will only be gradual, for the basic laws of physics apply. So we will be driving in cars that are much the same as today's, though safer and more efficient. We will be riding around in trains that look very much like the ones we will travel in to Paris later this year and go a little faster. And we will travel in aircraft that are merely a development of what we have already.
The revolution will come in communications and electronics, where the technologies of fibre optics and data compression will combine to race ahead. This will have a string of economic and social effects. For example, it will make communications very cheap indeed. We do not need to make heroic guesses about technology to say that in 25 years' time it will cost less than 10p in today's money to phone Australia . . . on a video phone. The technology exists now.
Cheap communications will change the world in much the same way as cheap air travel has done. Anyone whose work is largely screen-based can choose where they live. Countries with educated and numerate workers will be able to get into the new export market of 'white-collar' services. The Financial Times has much of its software written in India; workers in Ireland process US companies' insurance claims.
The hardest part is seeing the social implications of technological change and predicting what will become socially and politically acceptable. To what extent, for instance, will technology be used to cut crime? Few people would quarrel with video cameras monitoring shopping malls, or even city centres, but we might feel uncomfortable if this became the norm for suburban streets. Should there be a national DNA register for all criminals? Should it be extended to cover parking offenders? Or everyone?
It is the interaction between economic, technical and social change that presents the greatest puzzles. If electronic technology enables a significant minority of the population of the developed world to choose their location, the relationship between governments and people is bound to change. Governments will be rated on their performance not just by the people who elect them, but by would-be migrants. Countries will find themselves competing against each other in much the same way that US states do today.
At least in social questions it is possible to see the issues reasonably clearly, whatever judgement we make about the ways in which governments (and, more important, electorates) respond. When we move one stage further in the argument - to the political shape of the world a generation from now - however, even the issues seem unclear. And the better guide to what is to come may not be economics, but history.
Take the relationship between China and Japan, the most important political issue in East Asia. In overall economic terms, China will inevitably outstrip Japan, but Japan will remain far richer per head and have access to more sophisticated technology - technology China will need. It ought to be an ideal economic relationship. But you look back into the tangled history of these ancient cultures and ask how close an economic union these countries actually want.
Closer to home, look at the relationship between Britain and the European Union. It is extraordinary how ancient distrusts repeatedly threaten closer economic co-operation in petty ways: how uncomfortable we felt about BMW taking control of Rover; how the French sought to exclude UK airlines from Orly; how Germany is banning imports of British beef.
But history does provide a guide of sorts. Europe has a common culture which is quite different from that of North America, and that culture is the product of centuries during which the European peoples have lived together, quite often in harmony. It preceded the nation state - indeed several European nations are quite recent inventions. If Europe is seen as a collection of peoples, some long organised into nations, others not, it is possible to hazard a guess at how the political union of Europe might proceed. It surely feels more like a common cultural and economic entity than a common political one.
And the United Kingdom? Well, it is worth observing that these islands may make more sense split into the separate nations they once were than pretending that the present UK is the only appropriate constitutional model. But there we really do leave the worlds of economics and technological development far behind.
Paradoxically, it is much easier to see what will happen to world population or electronic technology than to predict whether it will take one generation or more for a lasting settlement to be reached in Northern Ireland, project how the former Yugoslavia will resolve its civil war or whether Western Europe, perhaps the most secular area in the world, will rediscover religion. But here we are in the realm of politics and psychology: beside these imponderables, even the arcane science of economics looks easy.
* 'The World In 2020', by Hamish McRae, is published today by HarperCollins, pounds 20.
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