Preserving the biodiversity of our planet will require some short-term sacrifices but in the long term it will benefit everyone, both economically and environmentally. Jaap de Roode reports

In the next 50 minutes another species will become extinct. By tomorrow we will have lost more than , and by the end of this century up to two-thirds of the more than 10 million species on earth might be gone.

To those who have not followed the biodiversity debate, these numbers may come as a shock. But for those working on ecological issues, it is just another in a long line of similar estimates - an estimate that shows that humans are probably better at wiping out species than the comet that hit the earth 65 million years ago, killing all the dinosaurs and half the other species.

There is no doubt that the biodiversity crisis is real, as the US National Academy of Sciences confirmed last year. There are already 30 times more people on the planet than biologists expect for an omnivore our size. An area the size of South America has been converted to cultivated land, and it is estimated that, as a species, we consume 45 per cent of the earth's total net biological productivity. With human populations growing and natural habitats decreasing, this crisis can only worsen.

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Endangered species and desperately poor humans often occupy the same land. For the latter to develop and preserve their countries' biodiversity might sound like an almost impossible quest. But ten years on from the Earth Summit in Rio de Janeiro there are already many examples of how sustainable use of natural resources can benefit human development and nature conservation. And on the eve of the World Summit on Sustainable Development in Johannesburg, ecologists have succeeded in proving that sustainable development actually makes economic sense. Expressing the benefits nature provides in US dollars, researchers, including the Oxford ecologist Norman Myers, showed in a recent issue of Science how investing in nature can pay.

Examples of sustainable development are numerous. In Costa Rica, the National Institute of Biodiversity is drawing up an inventory of the country's biodiversity with the help of communities living next to Costa Rica's national parks. In return for plant and insect extracts, drugs giant Merck gave the institute a research and sampling budget and royalties on any new drugs that might emerge as a result. Some of this money is being channelled directly into conservation efforts. Millions of third-world farms are already using low-tech innovations to increase their production. In Kenya, farmers plant weeds in their maize fields to give pests something else to eat, and in Costa Rica, windbreaks have been used to connect tree plantations and trees have been planted on pasturelands to protect forest birds and shade coffee plantations. In Zimbabwe, Campfire (Communal Areas Management Programme for Indigenous Resources) has given local communities control over their natural resources. They have benefited economically by trading natural products, such as crocodile eggs, timber and caterpillars, leasing sites to tourists, running tourist facilities, and by charging foreigners to hunt elephants, buffalos and lions. With the money earned, schools have been built and wells dug. Meanwhile, the population of large animals is either stable or increasing.

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It is obvious that human development can go hand in hand with conservation of biodiversity. But these examples, which cover areas such as agricultural products, medicine and ecotourism, are easy to quantify in economic terms. Over the past few years, ecologists and economists have come to realise that there are many other services that nature provides and that they too can be economically valued, though not as easily. Ecosystems, for example, can regulate biogeochemical cycles, protect soil, enhance crop pollination and control pests. As Myers says: "Tropical forests are like flywheels for global climate, and wetlands supply watershed functions for billions of small-scale farmers. We should be protecting those areas, even if there was no biodiversity crisis at all."

Putting price tags on concepts such as climate control and water supply has been problematic, but with an increasing understanding of the functioning of ecosystems and climate, it is getting easier. Building artificial water supplies, clearing away the devastation left by hurricanes and trading carbon credits are just a few ways that have allowed them to be valued. The effects of climate change caused by human interference thus show the economic benefits that nature can provide. The United Nations Environment Programme, for example, estimates that the overall economic value provided by nature is somewhere between $16 trillion (?10.5 trillion) and $54 trillion a year, a figure that is equivalent to the global gross national product.

Scientists have started to look into the economic benefits of wild ecosystems before and after conversion to human use. The Science study looks at Mount Cameroon and how the forest there can be used in a sustainable way through low-impact logging and selective logging of specific trees. Although oil palm and rubber plantations initially bring higher private benefits, they increase soil erosion and the risk of floods as well as decreasing carbon uptake because they cover less land and are less rooted in the soil. Overall, researchers have shown that total revenue from sustainable use outweighs the short-term benefits of the plantations.

In another example, the researchers compare mangrove forests in Thailand with the shrimp farms that are set up after clearance of the forests, and again show that the short-term gains from shrimp farms are offset by long-term effects of clearing the forests, such as lower protection from storm damage. One of the difficulties of doing this sort of evaluation is that the higher economic benefits often come from unmarketed services, such as climate control and soil protection, rather than marketed products such as timber and shrimps. The researchers argue that preserving those ecosystems requires compensatory mechanisms to mitigate the impact of losing private, local benefits. As unmarketed services serve the whole world, this should be an international effort, they say.

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Researcher Robert Costanza, an environmental economist from the University of Maryland, says there are several ways of making sustainability marketable, for example, through trading in carbon and biodiversity credits. He adds that sometimes there may not even be a need for compensation. For example, by chopping down the mangroves in Thailand, local people lose their traditional fishing grounds, but since they have never marketed them, they are not officially seen as providing any economic benefit. But if the mangroves are removed, local people migrate to the city "where they actually do get poor", Costanza says. So there is an economic gain in preserving the mangroves without the need for compensation.

The Science study also argues that investing in nature makes economic sense. The researchers calculate that expanding nature reserves worldwide so that they occupy 15 per cent of the land and 30 per cent of the sea will cost $45 billion a year, equivalent to 5 per cent of government subsidies in areas such as agriculture, fisheries and road transport.

At the same time the economic benefits extrapolated from the examples they worked on would be more than $4.4 trillion a year. Protecting nature and its habitats would thus offer benefits that are as much as 100 times higher than their cost. A "strikingly good bargain", as the authors point out. Sustainable development is possible and profitable, so our world leaders in Johannesburg will have very good reason to conserve them.

Jaap de Roode is a PhD student at the Institute of Cell, Animal and Population Biology, University of Edinburgh.

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