Overpopulation has become almost a forbidden concept. Thirty years ago, when there were around two and a half billion fewer human beings on the planet, the idea was actively debated. Many environmentalists accepted that smaller human numbers were necessary if humankind was ever to live in balance with the natural world, while the argument that there was no such thing as overpopulation was largely the preserve of free-market economists, doctrinaire Marxists and assorted religious fundamentalists. The debate was not always of the highest quality, with some advocates of population control making stark forecasts of imminent global starvation, and some of their opponents suggesting that a Green Revolution in agriculture would abolish hunger within a generation. Neither of these prospects was realistic, but there was a shared recognition that there might be a problem in rapidly rising human numbers.

Today, the very idea that there could be too many people on the planet has been abandoned as retrograde and anti-human. Green parties rarely raise the issue of population, saying that what matters is not the number of people but how resources are distributed among them; they insist that concern with population is a distraction from inequality and the immoralities of capitalism. No leader of any mainstream party in any country would dream of making population a key issue. The view that overpopulation is a figment of the dark reactionary imagination is undoubtedly the current orthodoxy. Yet there has not been a voice that could systematically articulate the prevailing wisdom – a gap that has been filled by Danny Dorling.

A professor of human geography at Sheffield and soon to be Halford Mackinder professor of geography at Oxford, Dorling aims to discredit any suggestion that the human species might be pressing up against the limits of natural resources. Peppering his argument with pained references to the few that persist in asking whether the planet might not already be rather crowded – David Attenborough and Joanna Lumley among those cited with purse-lipped disapproval – Dorling is the perfect anti-Malthusian. His account of the Essay on the Principle of Population (1798), in which the Reverend Thomas Malthus argued that the growth of human numbers would eventually be checked by shortage of food, follows a time-worn path. "It was the sexual hang-ups of a man of the cloth that resulted in ideas of population control making their political debut in 19th-century Britain." Originating in sexual repression, the idea of overpopulation tells a gloomy tale of the narrow limits of social improvement. "Human beings progress by telling stories," and it is a story of ongoing advance that we need. We should "learn to try not to estimate the carrying capacity of the Earth", but instead focus on possibilities of changing human behaviour. Population decline is already under way in some countries, and global human numbers will peak sometime this century. By telling ourselves a story about "how ten billion people can live well on the planet", we can exorcise the Malthusian phantasm.

Danny Dorling, Population 10 Billion

Though Dorling describes Population 10 Billion as "a book for pragmatists", it is actually intensely ideological all the way through. Reading his winningly simple narrative, you would not know that Malthus stands at the start of a long liberal tradition that acknowledged the dangers of rising human numbers but argued for contraception as the solution. The first economist to suggest (in 1848) that a zero-growth economy might be positively desirable, John Stuart Mill was a lifelong advocate of birth-control who – after discovering a newly killed infant under a pile of rags in St James's Park – was arrested on an obscenity charge and spent a night in prison at the age of 17 for distributing pamphlets offering practical advice on contraception to working-class women. Again, John Maynard Keynes – an admirer of Malthus who believed economics took a wrong turn when it departed from his work – suggested in his famous essay on "Economic Possibilities for Our Grandchildren" (1930) that more than enough wealth could be produced to satisfy human needs, but only if human numbers were stabilised by humane methods of birth control. Dorling doesn't mention these neo-Malthusian liberals because they don't fit the story he wants to tell, which is that the only limits on population are those imposed by oppressive human institutions.

There are larger omissions. In a book that recurs regularly to famines caused by western imperialism, there is no discussion of the politically engineered famine that cost millions of lives in the Ukraine in the early 1930s. Even more remarkably, Dorling manages to avoid the famine China suffered as a result of Mao's Great Leap Forward in 1958‑62. If you search for it in the book, you will find a single mention in the text, where it is cited in the course of a sentence listing four exceptions to continuing global population growth between the years 1851-1871. A reference directs the reader to a newspaper article, which an internet search reveals to be a review of Frank Dikötter's book, Mao's Great Famine (2011). But Dikötter's pioneering work, showing how tens of millions of people were starved, worked or beaten to death, is not discussed, while Yang Jisheng's taboo-breaking Tombstone: The Untold Story of Mao's Great Famine (2012) is not cited at all. One of the greatest human catastrophes is consigned to an opaque footnote.

An innocent reader might wonder why the largest famine of the 20th century, possibly in all of human history, should not be given a little more space in a book about population and resources. After all, Mao was no Malthusian – fired by a boundless sense of human possibility, he denied there could ever be too many people. Writing of the risk of a major famine in the middle of the current century, Dorling tells us such a famine will occur only if those with power "see others as less human than themselves". He goes on: "It is hard to think how this will happen unless hedge-fund morality becomes the norm and betting on future food prices is not curtailed." It's true that betting on food has had political effects – a speculative boom in grain prices helped trigger the Arab Spring in Tunisia and Egypt, for example. But the idea that hedge funds are the main obstacle to seeing others as fully human – let alone the only obstacle, as Dorling seems to suggest – is a parody of politically correct thinking. Despite disavowing anything that smacks of utopia or revolution, he seems to have persuaded himself that sectarian warfare in the Middle East, the re-emergence of the far right in Europe, enmity between China and Japan, as well as other awkward features of the contemporary scene, can be left behind if only we learn to tell ourselves new stories. He never doubts that "we" – he means people like himself – are becoming "a little less stupid". Reading him on the state of the world today, one can only wonder.

Here and there his book contains some useful insights. He makes short work of Matt Ridley's "rational optimism", and is right to suggest that we should start thinking about how to live with declining populations. One way or another, the spike in population is sure to come to an end and human numbers will then fall. But there is no reason for thinking this can be a peaceful process. Dorling welcomes the economic slowdown that has occurred in highly developed countries, and, in terms of the health of the planet, he is right; but the great majority of human beings want more growth not less, and any protracted contraction is bound to be accompanied by increased conflict. Believing planetary limits have been dreamt up to frighten us, he insists: "There is an alternative to fear." The alternative – wait for it – is "to stop buying things you don't need". Dorling invokes Marx on several occasions, always with respectful admiration. But Marx knew the human world is an arena of struggle and history more than a collection of reassuring anecdotes. Faced with Dorling's sermonising, he would have reacted with a guffaw of contempt.

Stephen Emmott, Ten Billion

Talk of giving up consumerism is reminiscent of Stephen Emmott's favourite example of a fashionable pseudo-solution for environmental problems: peeing while you're in the shower. Microsoft professor of computational research at Oxford, who founded and leads Microsoft's research laboratory in Cambridge, Emmott is singled out by Dorling as one of those who – following the devilish Malthus – invents nightmare scenarios. What Emmott in fact does – and this is the real difference between him and Dorling – is set the human animal firmly in the material world, where it actually lives. The planet does not care about the stories that humans tell themselves; it responds to what humans do, and is changing irreversibly as a result. As Emmott writes: "Right now, every leaf on every tree on Earth is experiencing a level of CO2 that the planet has not experienced for millions of years. How the planet's plants will respond to this we simply don't fully understand." While this unprecedented shift is under way, 40% of the planet's surface is being used for agriculture – a figure that will surely rise. Changes in diet, along with rising incomes, are part of the picture, but the expansion of agriculture is driven by one force more powerful than any other: the increase in human numbers. Ten thousand years ago there were only a million humans. As recently as 1960, there were only 3 billion. Today, there are more than 7 billion human beings, and there will probably be around 3 billion more before the century is over.

Every aspect of the environmental crisis is interconnected, and all of them flow from the pressure of population. As Emmott shows in powerful detail, it is human expansion that lies behind the conquest of our dependency on oil, coal and gas; the industrial-scale use of chemical pesticides, herbicides and fertilisers; battery farming; the transformation of fresh water into a depleting resource and the mass extinction of other life forms that is under way. Food production has become a branch of global industry, increasing our reliance on fossil fuels and accelerating the process of climate change. A mounting risk of famine is the result. In a roundabout process he couldn't have imagined, Malthus has turned out to be essentially right.

Emmott's short, highly accessible and vividly illustrated book marshals compelling evidence that "entire global ecosystems are not only capable of suffering a catastrophic tipping point, but are already approaching such a transition". He sees only two ways of dealing with what has become a planetary emergency: "The first is technologising our way out of it. The second is radical behaviour change." Emmott is sceptical about the first – particularly geoengineering schemes, which he views as highly risky – and sees no evidence of any readiness for radical behavioural change. "We need to consume less … And yet, every decade, global consumption continues to increase relentlessly." With neither technology nor politics offering any way out, Emmott concludes: "The problem is us … We urgently need to do – and I mean actually do – something radical to avert a global catastrophe. But I don't think we will. I think we're fucked."

Are we fucked, then? Well, it's clear we're in for a pretty rough time. The physical systems of the planet look like becoming more dangerously unstable. As Emmott explains, plumes of methane – a greenhouse gas many times more potent than C0 2 – have been observed rising from previously frozen areas off the Arctic shelf, and if the cause is melting ice triggered by human activities then the process could go on for centuries. The land grab in which rich countries and corporations are buying up arable land around the world will continue. Resource wars will multiply, and in a geopolitical struggle that has already begun the Arctic will become the site of the next Great Game.

"People are not bad when they have plenty of room," observed the Austro-Hungarian writer Joseph Roth. Emmott tells us that the violent spillover of environmental crisis is attracting the concern of military thinkers, and reports a young scientific colleague telling him that, looking ahead, he plans to teach his son how to use a gun. A course in computer hacking might be more useful, but the point is sound. While the planet is changing at a rate unknown in human experience, there is no prospect of any radical change in human behaviour.

That doesn't mean there is nothing that can be done. Unless climate change escalates to chaotic levels, the human animal will muddle through. A mix of declining fertility and technical fixes (including demonised technologies such as nuclear power) can help deal with the bottleneck in human numbers. The shift in thinking that will be needed if we are to prepare ourselves for living in a different world begins with reading Emmott's indispensable book.

• John Gray's The Silence of Animals: On Progress and Other Modern Myths is published by Allen Lane. Population 10 Billion: The Coming Demographic Crisis and How to Survive It by Danny Dorling is available from the Guardian Bookshop.