TWO DECADES AGO, the World Commission on Environment and Development began deliberating on the links between environment and economy. Chaired by Gro Harlem Brundtland, it came up with a long-standing and compelling definition for sustainable development – at the time, a new term: “Meeting the needs of the present without compromising the ability of future generations to meet their own needs.” Since then, I have counted a couple of hundred further definitions of sustainability, and the term has now entered our common language. Yet none better captures the core ideas of equity and justice set in a context of care for the world’s resources. But where are we now with this sustainability idea? Has it offered some new hope for the world, or has it effectively been a grand hoax?

In the 1960s, an iconic image captured the world’s imagination. Astronauts returning from the moon were able to photograph our Earth in the middle of empty, dark space. Here was our world, and there was only one, with a clear boundary. If something went wrong, there could be no external solutions, no rescue by cavalry riding over the hill. We would have to solve our own problems. This world, though, is now home to 6.4 billion people, and it is unimaginably complex. How would it look, by contrast, if we shrank it down to a single village of 100 people?

Our global village has twenty people in the North, fifteen of whom have 81% of the income; of the eighty in the South, twenty-two have less than $1 a day. The village has twenty-five hectares of cropland (four people for every hectare), a third of which is degraded. There are fifty-seven hectares of pasture and, perhaps surprisingly, still seventy hectares of forest. Food production in the village has increased enormously in the past four to five decades, and now there is enough to feed everyone plentifully – if they could access it, and if we didn’t feed much of the cereals to animals. But thirteen of the 100 people are permanently hungry, and, alarmingly, ten are obese. Other consumption figures are equally worrying. Villagers in the North American section consume 430 litres of water per day; in the South, twenty-three have no access to water. In the North, 100–230 kg of paper are consumed by each person annually; in the South, just 10–20 kg. In North America, there are seventy-five motor vehicles per 100 people; in Japan, fifty-seven; in Europe, twenty-seven; and in China, India and Africa, two.

This is the concern: the sustainable development literature often assumes that the world can be saved by bringing everyone up to the same levels of consumption as those in the North. We can, it is said, grow out of trouble. This is both a myth and a hoax. It cannot be done, as we would need six worlds at North American levels of consumption. And we simply do not have six worlds.

Lester Brown’s recent book, Outgrowing the Earth, begins by noting that the last half of the 20th century will be looked on as the “era of growth”. The world economy expanded seven-fold, and economic growth is now the goal of governments the world over. But whilst the economy has been growing, the world’s life-support systems have remained largely the same. There have been efficiency gains – more food from the same piece of land, better use of wastes, and so on. But these cannot offset the large drivers. If Americans have three cars for every four people, each emitting carbon to change the climate, what should we say to those Chinese who will wish to have the same?

Brown addresses five key themes: moving up the food chain efficiently; raising the Earth’s productivity; protecting cropland; stabilising water tables; and stabilising the climate. Two chapters focus on the pressing trends and dilemmas in China and Brazil, and a final chapter seeks to redefine security in terms of natural resources and food systems.

Throughout, there are enough figures to alarm even the most sceptical. Worldwide, 400,000 hectares of cropland are paved each year for roads and parking lots. The world motor vehicle fleet grows by 9 million annually. The 16 million hectares of land devoted to asphalt in the US are closing on the 21 million hectares planted to wheat.

There are, though, some over-simplifications in the drive to point to looming disaster, and these do the central thesis no favours. Deserts are assumed to be ever-expanding, even though the evidence in many places, particularly Africa, is that local communities have re-greened their lands successfully. Rangelands are assumed to be degrading because of mismanagement, yet closed-access commons have long been well managed. One whole chapter addresses the population problem, and this is where a limited time horizon and an assumption of Malthusian mechanics make for misconceptions. The ever-growing world population is taken to be a problem in itself. In fact, it is aggregate consumption that is critical.

We know that the world population will continue to rise for two generations, but will stabilise by 2040–50 at around 9 billion. This is substantially more than today, and is a major challenge. But after this time, population will stabilise, and then probably fall, owing to declining fertility rates. And this is where there is some long-term hope. The United Nations has heroically forecast world population changes 300 years hence, and at medium and low fertility rates the world population will have fallen to between 4 billion and 6 billion by 2150. This is not well known, and yet it should be central to how we think about protecting our world. The key problem, then, centres on what we do in the next two generations to solve our over-consumption problems.

Should we be pessimistic or optimistic? At the global level, I think the former. At the local level, probably the latter. There is so much that is good centred on local communities. But can we scale these up to a seemingly indifferent world? Perhaps we should reflect on what the Mayans in Central America might have been thinking at the end of their 600-year Classic Period in 900 CE, when they were living in some of the largest and most sophisticated settlements in the world. They probably thought they would go on forever; that their progress represented the pinnacle of human endeavour; that they were somehow untouchable. Yet their civilisation mysteriously disappeared in the blink of an eye, leaving only ruins in the rainforests, indecipherable glyphs, just three books, and many long-standing mysteries for later archaeologists.

Jules Pretty is Professor of Environment and Society at the University of Essex.