The Washington-based institute, one of the world's most influential environmental think-tanks, yesterday published Vital Signs 1993*, an attempt to measure the health of the planet. The more than 30 'vital signs' - ranging from energy efficiency and atmospheric temperature to wind- power capacity and bicycle sales - aim to do for the global environment what indices of trade, production and GDP do for its economy. But the analogy can be carried much further. According to Worldwatch, the spillover effects of environmental degradation are now seriously undermining economic performance: we have reached some sort of turning-point.
Consider the following. Air pollution of Europe's forests costs an estimated dollars 30.4bn ( pounds 20.26bn) a year in lost wood and jobs, increased flooding, soil losses and the silting of rivers. Degradation of drylands - four-tenths of the earth's land area - costs dollars 42bn a year, roughly the value of the US grain harvest, in lost crops and livestock. Pollution in the former Soviet Union has led to a decline in life expectancy and higher health costs.
The cost of global warming to the US, meanwhile, has been put at 1 per cent of GNP. Water scarcity, says Vital Signs - the world has one-third less water per person than in 1970 - is limiting economic expansion and threatening conflict in regions such as Africa, the Middle East and China.
The first lesson of such figures is that environmentalism can no longer be considered a Western middle-class whim: the world's economic prospects rest on the health of its environment. Conventional economic wisdom attributes the recession of the early 1990s to mismanagement in the industrial countries. Not so, says Worldwatch. Nature's constraints are now 'directly affecting global economic trends'. And nowhere is this truer than in food production.
According to Vital Signs, the world is entering an era of protein scarcity. In the 1980s it finally reached those global limits of which the 1970s warned (and at which right-wingers scoffed). First, the area of cropland, having peaked at 735 million hectares (1,816 million acres) in 1981, is now static at around 695 million hectares. Second, the global fish catch is also static, at just under 100 million tons - roughly the figure scientists believe is the maximum sustainable yield of the oceans. And third, there are 91 million new mouths to feed every year.
Since 1984, in consequence, grain production per person has, for the first time, been falling. Can't new land be brought into production? Probably not - erosion, topsoil losses and urbanisation make such prospective gains largely illusory, says Worldwatch. What about higher yields from the existing area? Much of the scope for increased productivity from fertilisers has been exhausted; since 1989 world fertiliser use has declined.
Add global warming to such equations and you arrive at Lester Brown's nightmare scenario. Traditionally the United States has been the world's grain banker but in 1988 the American harvest failed massively and the US had to dip into its reserves to maintain its exports - normally about one-third of production. Suppose we have another year or two of heat and drought like 1988 - a likely prospect with a warming planet - and the US harvest fails again, exhausting its reserves? Where does Japan, the world's largest importer, go for its grain? Will a strong yen outbid a weak dollar for home-grown US wheat? Will the American administration slap on controls, precipitating a trade war?
Mr Brown believes that the 6 per cent decline in grain output per person between 1984 and 1992 is the 'most disturbing economic trend in the world today'. The West may think its purchasing power may cocoon it from world hunger but it is a calculated risk: a starving world is an unstable world. Possible scenarios include debt defaults, mass movements of refugees or the spread of trigger-happy anti-Western regimes.
Global stability, in short, may rest on some subtle dietary trade-offs. With production of protein - fish, meat and soya beans - slowing or static, but population growing by 91 million annually, we need to eat less, or differently. At its most simple, do we eat grain or feed it to cattle?
Hence the exhortation to eat less meat. A cow is a relatively inefficient means of producing protein: far better to turn the land over to soya beans. In land-use terms, a non-meat diet is between two and three times more efficient: it would thus effectively 'create' large additional areas of cropland. Many people who have cut out meat from their diet - an estimated 7 per cent of Britons - have probably done so for reasons of animal welfare. But there is a much greater altruism involved - the prevention of mass starvation.
*Vital Signs 1993, Earthscan, pounds 9.95.