The Food and Agriculture Organization (FAO) maintains that global food supplies will have to double by 2025, if the world is to provide adequate diets for 8.5 billion people. Many experts believe it is possible. They argue that faster-growing, hardier varieties are being developed; pest and weed control are more sophisticated; fertilizers can be used more effectively; and alternative methods are being brought into use.

Plant breeders have rediscovered some of the world's "forgotten foods" such as amaranth and quinoa, which were grown by the Incas and Aztecs of Central and South America. Both are versatile, hardy grains packed with vitamins and minerals. FAO reckons there may be as many as 500 other types of forgotten foods awaiting cultivation.

Others point to the tremendous strides made by aquaculture and mariculture enterprises over the past decade. Fish and shellfish farming is now big business: in 1993, 16 million tons of farmed seafood was produced worldwide, with prospects for future increases.

Critics question whether such optimism is justified. FAO figures show that land is going out of production as a result of a wide spectrum of environmental damage, from salinization and waterlogging to dessication and loss of topsoil. Availability of fresh water is an increasing problem in many agricultural areas, even as urban and industrial expansion are increasing demands for water. About half of the world's poor live in environmentally fragile rural areas.

• An area larger than the United States and Mexico, mostly in the dry topics, is suffering from moderate to severe soil degradation. More than 55 per cent of this damage is caused by water erosion and 33 per cent by wind erosion.

• Currently, soil erosion and other forms of land degradation rob the world of between 5 and 7 million hectares of valuable farming land each year. Moreover, soil erosion seems to be getting worse: about 25 billion metric tons of topsoil is lost per annum, mostly from erosion and poor land use practices. Globally, soil erosion jeopardizes the livelihoods of close to 1 billion people.

• Although the world has about 240 million hectares of irrigated cropland, there may be less room for expansion than agronomists contend. The irrigated 17 per cent of the world's cropland is two and a half times as productive as rainfed cropland and produces one-third of the world's food. Half of this area is now affected by waterlogging and salinization. Expanding food production through irrigation may be more expensive than poor countries can afford.

• The world may already have reached the upper limits of capture fisheries. In 1995, FAO reported that nearly 70 per cent of the world's marine fish and shellfish stocks were fully to heavily exploited, over-exploited, depleted or slowly recovering. Of the 15 major fishing areas (as defined by FAO), the productivity in all but two has fallen since the peak year of 1989.

• Unless they are carefully managed and maintained, fish farming operations can seriously degrade coastal waters, causing algal blooms that deplete the water of oxygen. They also question whether fish farming will be ever enough to offset the projected losses in capture fisheries, especially given ever-increasing demand.

• Freshwater resources are showing increasing signs of stress. According to Population Action International, by the year 2025 some 48 nations containing 3 billion people will be facing water shortages. China's renewable water resources, for example, can support sustainably only half of its current population of 1.2 billion people. To meet the shortfall, China must overdraw its groundwater supplies, as well as clean and re-use surface waters.

•  The world is increasingly dependent on a narrow selection of staple foods. After 10,000 years of settled agriculture and the discovery of more than 50,000 species of edible plants, only a few hundred contribute significantly to global food supplies. Of these, no more than 15 provide 90 per cent of the world's food energy intake; and three--rice, maize and wheat--are staple foods for 4 billion people. FAO estimates that since the beginning of the 20th century, about three quarters of the genetic diversity of agricultural crops has been lost. The world is becoming increasingly dependent on fewer and fewer crop varieties and, as a result, must cope with a rapidly diminishing gene pool. Plant geneticists worry that new disease pathogens, unknown to science, could decimate domestic cultivars of maize, wheat or rice triggering serious food shortages in some developing countries.

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