Sustainability - to keep going continuously at a certain rate or level - has deservedly become the central criterion by which environmental well-being is measured. On this basis the human species has become a hazard not only to itself but to the other 10 million or so species on the planet, according to the Millennium Ecosystem Assessment, an authoritative report by 1,360 scientists from 95 countries under United Nations auspices.
This sober and devastating document lays down indicators for environmental sustainability and outlines a timeframe within which action should be taken to reverse the dangerous trends involved. It warns that "tipping points" are close at hand in spheres such as climate change, the spread of new diseases, the penetration of habitats by species which are alien to them, the effects of algal blooms, coral reef decay and the collapse of fishing stocks. These trends are not irreversible; but they are based on a frightening acceleration of change over the last few decades which will intensify in coming years. They therefore demand attention and action by world leaders and peoples, on the elementary prudential basis that otherwise we will not survive.
Among the rapid changes cited are an increase in world population from three to six billion people since 1960. More land has been reclaimed in the last 60 years for agriculture than in the whole period from 1700-1900, with some 24 per cent of the world's surface now cultivated. Since 1980 one quarter of fish stocks have been wiped out, there has been a 35 per cent increase in algal blooms arising from the production of nitrogen and a huge increase in the use of fresh water by humans. Deforestation and desertification are proceeding apace. Granted that a greatly increased human population is feeding itself by increased productivity and ingenuity, there is nevertheless a huge build up of pressure on the resources needed to reproduce human life.
Urgent action is required to tackle these dangerous trends. This report is not without hope in face of them, but it insists a new kind of leadership is required from governments, business organisations, civil society groups, scientists and citizens. It must be based on a clear recognition that while there is no simple fix for environmental degradation, unless it is tackled collectively it will not be possible to sustain life. This is the most basic existential task facing any species, including our own. Natural history is replete with examples of failures to take such action - but there are also many cases in which warnings have been heeded successfully.
As the report says, "we may have distanced ourselves from nature, but we rely completely on the services it delivers". A valuable exercise in accounting calculates the "free business services" provided by nature, such as the pollination of crops or the air conditioning provided by wild plants, at $33 trillion, almost twice the annual global product. We now know better how much we are living on borrowed resources and time.