Daniel Franklin, the executive editor and business affairs editor at the Economist, is a tentative chap for a prognosticator. As well as editing this round-up of seers' views of the four decades ahead, he and his co-editor John Andrews are also responsible for the Economist's annual publication on the coming year "The World in ". Perhaps it's this workaday familiarity with the imperfections of futurology that makes Franklin so keen to distance himself from any great likelihood of being right.

In his introduction to these 20 essays by his colleagues he says that, while identifying the trends that are transforming the world right now is eminently possible, foreseeing how they may shape the world in 2050 is "absurdly ambitious. History is littered with prophecies that turned out to be utterly wrong." He then cites just two of these clunkers: the radical journalist HN Brailsford writing in 1914: "My own belief is that there will be no more wars among the six Great Powers", and the Economist Irving Fisher predicting a stock market rise a week before the 1929 crash.

Indeed, throughout the whole of Megachange, the impossibility of predicting the future is a strange and persistent lament, ever encouraging the reader in search of experts prepared to boldly go there to chuck the book into the nearest bin. But for all that, the examples of failed anticipation listed here are remarkably few  excepting Matt Ridley's bizarrely tendentious rant in the concluding essay, of which more anon.

To counter Franklin's rather nutty point about Brailsford in 1914 it is sufficient only to observe that between the publication of The Battle of Dorking in 1871 and the beginning of the first world war some 400 novels anticipating conflict between Britain and Germany were published in English alone  so many predictions of the coming Armageddon that they constitute an entire sub-genre of late Victorian and Edwardian scientific romance called "invasion literature".

As to Irving Fisher, it seems strange that Franklin alludes to him only as "an American economist", when in fact Fisher was the first star economist of the 20th century; and while Fisher's neo-Keynsian response to the great depression was discredited by his own failure to anticipate the crash, his later work on the foundations of the quantity theory of money made him one of the founding fathers of the Chicago school of economists, those scourges of union-orchestrated wage inflation, to whom we owe so many of the blessings of Reaganomics.

Of course, there were other economists who understood long before 1929 that capitalism would always be subject to periodic crises of an increasing severity  preeminent among them was a certain ticket-holder at the British Library, one K Marx  but while several of the contributors to this volume pour scorn on Marxian millenarianism (possibly because they have no real understanding of dialectical materialism), none is prepared even to acknowledge the foresight of other prophets  Vico, Spengler, Toynbee  who understood history to have, at best, a rather vicious circularity.

So, instead of a steely-eyed look ahead, Megachange offers us a straightforward survey of the world as it is today, together with a lot of future hedging. Thus the text is bedizened with these qualifiers: "it may well be", "probably", "possibly" and indeed "likely" appear so often that the casual reader might well be lulled into thinking these Economist stalwarts are genuinely sceptical about their claims  but don't be fooled. Franklin sets out their stall thus: "there is every chance that the world in 2050 will be richer, healthier, more connected, more sustainable, more productive, more innovative, better educated, with less inequality between rich and poor and between men and women, and with more opportunity for billions of people." To which clap-happy optimism one might well cry out "Praise the Lord!" were it not the case  as Anthony Gottlieb skilfully deduces in his essay "Believe it or not" on the future of religion  that rising prosperity and equality inevitably does away with silly old superstitious deism.

At the core of the Economist posse's thinking lie  suitably enough  two simple statistical projections. One is demographic: the slowing down of global population growth takes the form of a baby-boomer bulge that rolls around the earth from west to east (with the exception of China) and from north to south. The implications of this are that while the western economies slow down over the next half-century, those of Asia and Africa speed up as they have, proportionately, more people in their workforces.

In tandem with this demographic charger pulling Helios's chariot across the skies is that other great workhorse: growth. Say what you will about those nags War, Pestilence, Famine and Civil Disorder, the stats are indisputable: the world's economy just keeps on growing; indeed, apart from a miserable little glitch in 2009, it has grown every year since 1945. Therefore, following that fine piece of reasoning, post hoc, ergo propter hoc, it will continue to do so, with the redistributed population alone assuring its more equitable distribution.

Lest I make the Economist writers sound too simplistic, let me point out that they also adduce all sorts of other factors to explain how the 9 billion earthlings of 2050 will be living happily with an average income of $20,000 per annum (by today's standards). As any fool knows, along with growth, what capitalism does best is innovation  and there will be innovations aplenty. Biotechnology will heal us, information technology will connect us, and there will even be new gizmos in the political science marketplace, leading to more genuinely democratic and free societies: greater public-spiritedness  fostered by Twitter, Facebook and their descendants  will be matched by bloated governments being slimmed down, and their economically wasteful social security functions being devolved into public-private partnerships. Whoopee!

As for that methane-emitting elephant in the room, global warming, worry ye not! In "Feeling the heat", an otherwise exemplary description of the current parlous state of global ecology, Oliver Morton looks forward to a mid-century in which good old human can-do still manages to muddle through: "The challenge is not to solve a problem," he says, "but manage a panoply of risks at every level from that of the farm and city, up through the state and region to the globe itself."

Actually, I think Morton is quite right to dismiss the "big problem  big solution" to global warming that's been enshrined by the unachievable targets of Kyoto and Copenhagen, but although he also honestly sets out the unknowable future course of such warming, he shies away from considering in hard environmental terms what the International Panel on Climate Change's upper range of temperature forecasts will mean  and not just for business, but you, me, and most pertinently, the Sudanese woman dragging her way through desertification to the nearest empty well.

While Morton is relatively sober about global warming, its impact hardly intrudes on the Panglossian prognosticators that surround him in this book. For them, the world in 2050 is pretty much business as usual, ie: bigger, faster and more profitable. I suppose it's hardly surprising that those who write for a magazine called "The Economist" are so sold on the notion that sheer quantity is itself a sufficient measure of the good life. In this rabid utilitarianism  which understands the price of everything but the value of nothing  they are the unlikely bedfellows of that arch-moderniser Josef Stalin, whose mantra it was that "Quantity has a quality all of its own". However, if you ask me, that quality is largely  bullshit.

And then there's Matt Ridley. Ridley, author of The Rational Optimist and the former non-executive chairman of that great capitalist success story Northern Rock, gets to make the plenary speech at this convocation of anti-Cassandras. There's something almost insulting in allowing him this space, given that under his watch Northern Rock was bailed out with a liability to the British taxpayer of £3,287 per household (figure courtesy of an institution beloved by all economists, the Office of National Statistics), and Ridley doesn't disappoint, filling it up with the kind of pop-eyed and factually threadbare climate change scepticism that has already been thoroughly discredited by George Monbiot in the pages of this newspaper and elsewhere. Ridley also gives a long list of some recent prophesies of doom that have failed to materialise  from the millennium bug to a mad cow pandemic.

I suppose it isn't that surprising that Ridley should be the figurehead on this particular ship of fools: the Economist was no better than any of the mainstream economics pundits at spotting the looming iceberg of 2007-8, and it's presumably some residual conscience about this that underpins all their hedging. But while quantifiers almost always make lousy futurologists there are qualifiers who are often very good at it indeed. Think of EM Forster accurately foretelling the internet and the worldwide web in his short story "The Machine Stops" (1909), or Edgar Allan Poe, who foretold genetic engineering even before the discovery of genes themselves  or for that matter, HG Wells, who managed  by dint of sheer prolificity  to predict just about everything. So if you want to know what the world might actually be like in 2050 you'd do better to browse in the science fiction and fantasy section of your local online retailer, which is where Megachange properly belongs.

Will Self is professor of contemporary thought at Brunel University; his new novel Umbrella will be published by Bloomsbury in August.

The authors of this book are often humble in the face of their own predictions  perhaps, as the preface notes, because history is littered with false prophecy. But through a delicate process of analysis  and a large amount of guesswork  the Earth is imagined 38 years from now; the idea being to illustrate the rapid growth, or "Megachange", we are currently experiencing, and to hypothesise about where this will lead us.

The various contributors, who are all part of the Economist's "extended family", believe that there will be too many people, too little food and a warmer planet; but there will be more jobs, food substitutes and a solution to global warming (even if that solution is finding life on other planets). The book speaks matter of factly about our prospects, and is punctuated with graphs and tables enabling the reader to glide through difficult topics with relative ease. Megachange is not exactly groundbreaking, but it is an intriguing and at times uplifting set of essays on why we shouldn't completely fear for our children.