Throughout history, technological innovation has saved us from being overwhelmed by overpopulation, and Jesse Ausubel tells Alison George why he is convinced that human resourcefulness can pull the fat out of the fire even now

You're known as a techno-optimist. Why have you got such faith in technology's power to save the environment?

I regard myself as neither an optimist nor a pessimist. But I do think that humanity is ingenious and enterprising. Throughout the ages people have doubted that their descendants could exist, with improving health and longevity, in the numbers and densities we do now. In the 19th century it was common to reason that horse manure or chimney smoke would bury or choke cities. Yet air quality in New York City and water quality in New York harbour are better than when I or my mother was a child. Over time people find, invent and spread solutions for many environmental problems.

So do environmental doomsayers fail to factor in our technical ingenuity?

Malthus certainly underestimated technical change. And numerous people considered experts in the 1950s, 1960s and 1970s thought that humanity would not make it to 2009 without big collapses in population, at least regionally. It didn't happen. As a student in the early 1970s, I shared the tremendous interest in Garrett Hardin's 1968 Science article "The tragedy of the commons", which described how herdsmen selfishly add cows to the common pasture until the resource fails for all. In the tragic instances, individual rationality does destroy the collectivity.

Surely our inability to limit ourselves is a major issue.

Some recent research suggests organisms do try to sense limits. Even bacteria turn out to have networks of social communication and to use something called quorum sensing to coordinate their gene expression according to the local density of their population, and so avoid disastrous growth. Viewing normal biological behaviour only as the selfish myopia of the tragedy of the commons contrasts with our emerging understanding of quorum sensing factors, a growing appreciation of altruism and other discoveries in biology and behaviour.

You could say that fear-inducing articles like Hardin's are social equivalents of quorum sensing factors, and we have responded to the signals. Farmers have lifted yields to produce more crops without using more land. Engineers have improved the efficiency of power turbines so that the primary energy needed to serve today's population is much less than if we were still using the engines of Malthus's era or those of 1968. In general, humans are involved in "resource sparing" - the increasingly efficient use of land, energy, water and other materials that allows humanity to grow in numbers, lifespan or level of consumption while stopping the burden on nature from becoming too disastrous.

Won't there come a point, though, when we can't sustain any more people?

No convincing answer exists to the question of how many people Earth can support. Environmental impact derives from a combination of population, affluence, preferences in consumption, and the technology used to produce goods and services. Population and affluence may multiply environmental impact, but changes in technology, consumer preferences and other behaviour can more than offset the multipliers. A look back over 50 years shows success stories, such as urban air quality and the regrowth of temperate forests, as well as cases where the result has been more damaging. The democratisation of sushi is an example of a negative case, as an increase in the number of affluent people with a taste for seafood has been disastrous for bluefin tuna.

Are there any specific changes that would help the Earth support such large populations?

Reading e-books and articles online is already driving newspapers and magazines to stop printing hard copies, thus sparing lots of forest that would have been turned into paper. Light-emitting diodes illuminate far more efficiently than traditional incandescent light bulbs. Viagra spares tiger bone and rhino horn. A vegetarian diet requires about half as much acreage as a meaty one. If people vastly reduced their consumption of meat, humanity would spare a lot of land for nature.

You've said that we could feed 10 billion people on half the area we currently use by improving agricultural efficiency. How would that work?

High yields are the best friend of nature. Even if humans remain carnivorous, if we continue lifting yields at roughly 2 per cent per year, as farmers have achieved over the past 100 years, then simple arithmetic shows lots of land now farmed will be abandoned and can return to nature. The world population is increasing by only around 1 per cent per year, so sustaining 2 per cent yield growth could free half of farmed land over 75 years or so. The highest yields that have been achieved in China, India, the US and many other countries are typically 300 per cent of average yields, so 2 per cent yearly gains are not miracles. They are business-as-usual, but with a lot of sweat.

Do you really think it is feasible that the Earth can support 20 billion people?

Yes. And many qualities of the environment could rise. With my colleagues I have laid out some of the technology and behaviour that would allow large populations to prosper while harmful emissions plummet and large amounts of land and sea are freed for nature. The technologies include 5-gigawatt zero-emission electric power plants burning natural gas, and magnetically levitated trains running in evacuated tubes underground.

Forest area and volume are key indicators of environmental quality. In the 1970s, prospects for forests seemed bleak. Yet since about 1990 in many areas of the world, even in the Congo basin, forests are regrowing. Human respect for the oceans, however, lags a century or so behind our appreciation of the terrestrial environment. Clean aquaculture of herbivores and fooling carnivorous fish into eating tofu in neatly enclosed farms matters a lot, unless we resist the temptation to enjoy seafood.

Your bottom line, then, is that technological advances can alleviate the environmental downsides of increased population.

Technology has liberated humans from the environment. Today we live about equally well in polar and tropical, arid and wet environments. The new question is whether humanity can use technology to liberate the environment itself. E-books, landless agriculture - farming that uses very little land because of high yields - and subterranean maglevs show the way.

Read more: The population delusion

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