When science fiction writers envision possible futures for the world, their cultures' serious expectations about the real or probable future unavoidably shape those visions. Consider, for example, the many novels of the 1950s and 1960s set in worlds recovering from a nuclear war, such as Andre Norton's Star Man's Son, Edgar Pangborn's Davy, or John Wyndham's Re-Birth.

In more recent decades, one of the most prevalent such visions, and the focus of as many fears as nuclear war, has been environmentalism and its predictions of global ecological catastrophe. The Skeptical Environmentalist: Measuring the Real State of the World offers an invaluable assessment of how well founded those fears really are.

The Skeptical Environmentalist - Bjorn Lomborg Its author, Bjorn Lomborg, a professor of statistics at a Danish university, describes himself as "an old left-wing Greenpeace environmentalist". In 1997, reading an interview with Julian Simon in Wired Magazine ("The Doomslayer" by Ed Regis), he saw Simon's claim that environmentalist fears are not supported even by the actual governmental statistics that environmentalists cite to support their views.

Lomborg organized a seminar to assess Simon's claim by careful review of the actual statistics — it was exactly the sort of project that's best suited to teach research and analysis skills to students. In his own words, "we expected to show that most of Simon's talk was simple, American right-wing propaganda". Much to his and his students' surprise, the great majority of Simon's claims were supported by the evidence.

The Skeptical Environmentalist documents that conclusion. Most of its content is a straightforward review of factual evidence on a wide range of topics: resource exhaustion, pollution, human health and prosperity, and future threats of global warming and mass extinctions.

The evidence on most of these points shows that conditions grew steadily better during the late 20th Century, the very period when environmentalists often claimed that they were getting steadily worse. For example, the proportion of people starving in Third World countries has decreased over recent decades; in fact, despite massive Third World population growth, the actual number of people starving has fallen from 920 million in 1971 to 792 million in 1997. Certainly this isn't ideal, but it doesn't represent catastrophic failure of the food production system. And similar lessons can be drawn for most other issues.

Interspersed with these masses of data are occasional theoretical analyses, often turning on economic principles. There are historical perspectives, such as a discussion of Stanley Jevons' The Coal Question, originally published in 1865, which predicted that English industry would soon end when the coal mines ran out. (Every futurist ought to read Jevons — not because of what he got right, but for the cautionary effect of seeing what he got wrong. For example, Jevons mentioned solar energy but dismissed petroleum on the ground that, since it was not used as fuel at the time, it never would be an important fuel.)

And Lomborg gives pointed criticisms of leading environmentalists, such as Lester Brown of Worldwatch Institute, and Paul Ehrlich. While sharing environmentalist goals, Lomborg does not believe that either science or the environment is served by biased interpretations of the evidence, and still less by wild claims that derive from no factual evidence at all — and he cites many examples of both.

Libertarianism need not be hostile to the environment; private property rights and the framework of common law offer the best way to protect the environment, and free markets in fact embody the same diversity and decentralization that ecologists praise in the nonhuman world. Libertarians do have many disagreements with environmentalism as a movement. Often these come down to appeals to conflicting theoretical and philosophical perspectives. But Lomborg presents the factual evidence to show that the libertarian perspective is a better model of the real world. And that same evidence will be well suited to the needs of science fiction writers, libertarian or otherwise, who want to envision more plausible and realistic futures as settings for their stories.

Bjørn Lomborg's The Skeptical Environmentalist caused an almighty stink when it was published in Denmark in 1998, and the English translation looks set to do the same over here. Lomborg's beef is with the litany of doom espoused by certain environmental activists. We've all heard the main points many times: natural resources are running out; the world's population is too big and growing at an alarming rate; rivers, lakes, oceans and the atmosphere are getting dirtier all the time. Forests are being destroyed, fish stocks are collapsing, 40,000 species a year are going extinct and the planet is warming disastrously. The world is falling apart, in other words, and it's all our fault.

Nonsense, says Lomborg. These are just scare stories put about by ideologues and promulgated by the media. There is little evidence that the world is in trouble, he claims, and a good deal more that suggests that we've never had it so good. Air quality in the developed world has improved markedly over the last 100 years. Human life expectancy has soared. The average inhabitant of the developing world consumes 38% more calories now than 100 years ago, and the percentage of people threatened with starvation has fallen from 35% to 18%. The hole in the ozone layer is more or less fixed; the global-warming threat has been much exaggerated. And though we worry incessantly about pollution, the lifetime risk of drinking water laden with pesticides at the EU limit is the equivalent of smoking 1.4 cigarettes. In short, the world is not falling apart; rather, the doom-mongers have led us all down the garden path.

Environmental intervention is also unconscionably costly. Implementing the Kyoto Protocol on carbon dioxide emissions is likely to cost $161-$346bn, and the average temperature of the Earth will probably be about the same in 2100 with Kyoto as in 2094 without it. In other words, Kyoto will buy us six years. In contrast, several million deaths could be prevented each year by securing clean drinking water and sanitation for everyone at a one-off cost of $200bn. To think that our politicians would abandon Kyoto and spend the saved money on wells and drains would be naive in the extreme, but the figures should give every concerned individual pause for thought.

"Lomborg" is the dirtiest word in environmental circles at the moment. Henning Sørensen, former president of the Royal Danish Academy of Sciences, maintains that his fellow countryman is wrong, dangerous and lacking the professional training even to comprehend the data he presents. These are strong words. Sørensen was referring specifically to Lomborg's opinions on mineral resources, but this book contains sufficient biological nonsense to add ignorance of at least one more discipline to the charge sheet.

For example, long-term growth in the number of species on Earth over the last 600m years - itself a disputed issue, though you wouldn't know it - is accredited to "a process of specialisation which is both due to the fact that the Earth's physical surroundings have become more diverse and a result of all other species becoming more spe cialised". Eh? One really has to look further than a UN Environment Programme Report to understand such complex issues. And surely only a statistician could arrive at a figure of 0.7% extinction of all species on Earth in the next 50 years, when respectable estimates of total diversity range from 2m to 500m species (not 2m-80m, as Lomborg claims). Having said this, I prefer Lomborg's absurdly precise estimate to Paul Ehrlich's outrageous 100% extinction by 2010.

My greatest concern, however, is with Lomborg's tone. He is clearly committed to rubbishing the views of hand-picked environmentalists, frequently the very silly ones such as Ehrlich, whom professionals have been ignoring for decades. This selective approach does not inspire much confidence: ridiculing idiots is easy. Who better to manipulate data in support of a particular point of view than a professional statistician? And who to trust with the task less than someone who argues like a lawyer?

The reader should be wary in particular of Lomborg's passion for global statistics: overarching averages can obscure a lot of important detail. The area of land covered with trees may not have changed much in the last 50 years, but this is mostly because northern forests have increased in area while the biologically richer tropical ones have declined. If you want to see how the global trend translates into one particular local context, go to northern Scotland and gaze over the immense plantations of American conifers that have replaced our biologically unique native peatlands. And to balance the books, the area of these noisome tree farms has to be reflected by deforestation somewhere else in the world - Madagascar, perhaps. That global forest area has remained more or less constant actually tells us nothing about the state of the environment.

So have we been led down the garden path by environmentalists? Lomborg argues a convincing case with which I have much sympathy, but the reader should perhaps follow the author's lead and maintain a healthy scepticism. And if you come away with the nagging suspicion that Lomborg has a secret drawer of data that do not fit his convictions, then you are quite probably a cynic.