What China's worst environmental problem is depends upon who one asks. Chinese experts believe water pollution is the biggest problem because the largest number of people are affected by contamination of both surface and groundwater. Those with another perspective might say that air pollution is the worst problem, because the Chinese ambient concentrations of particulates, sulfur dioxide, nitrogen oxides, and other pollutants are some of the highest in the world. Globally oriented scientists might say that China's emissions of greenhouse gases are its biggest problem, and will soon swamp the world, though this problem is not seen domestically as a pressing one.

According to Smil, deforestation is China's biggest environmental problem. China is cutting less roundwood than a decade ago, and it has also made progress in afforestation. But because of the amount of recent cutting and replanting, China now has a large proportion of very young forests which will not be available for commercial logging for decades. Consequently, the total number of trees may be increasing, but the volume of mature timber is still declining. This disparity brings up an important point with regard to the quality of data coming out of China. In general, data accuracy is quite poor and careful interpretation is necessary for all but a few basic data sets, such as most population and some industrial output statistics.

There are also major problems with how the Chinese economy is represented in international statistics. Per capita Chinese income is much higher than is widely known. One problem is that Chinese money should not be translated to U.S. dollars using the official exchange rate which has been steadily declining since the early 1980s, while the Chinese economy has grown more than any in the world (except South Korea). A more appropriate measure of Chinese economic strength might be per capita purchasing power, which falls most likely between $1500 and $2000.

In regard to the economic costs of China's environmental problems, Smil cited Chinese studies which found that 6 to 8% of Chinese gross domestic product (GDP) is lost to environmental pollution, leaving aside biodiversity losses and other hard-to-quantify values. More recent studies find that the effects of air, water, and land pollution and ecosystem degradation cost the country up to 15% of its GDP every year. Meanwhile, China spends less than 1% of GDP per year on these problems and so could clearly benefit by increasing this investment.

Deforestation is the costliest of China's environmental ills. The amount of soil lost from deforested land is massive -- up to several orders of magnitude greater than that lost from well-treed land, reaching hundreds of tons per hectare. Because China irrigates more land than any country in the world, and because it also relies heavily on hydroelectric generation, silting of streams and reservoirs results in serious economic losses. The main costs involve shortened lifetime of water storage, and the necessity of more frequent canal dredging. Furthermore, nitrogen loss in eroded topsoil is equal to the total amount of the nutrient applied in fertilizer, that is about 20 million tons. The cost of this loss is estimated at $20 billion a year.

Commercial harvesting of wood, both legal and illegal, is just one cause of deforestation. There is also still a good deal of wood harvesting for household cooking and heating. The availability of household fuel has increased significantly with the opening of many small coal mines during the 1980s, but in many areas, wood is still harvested for basic fuel. There are great province to province differences; in the northern provinces, cutting has decreased because of coal availability, but in the southern provinces, there has actually been an increase in wood cutting.

On the subject of land for food production, official Chinese statistics put China's farmland at 95 million hectares, but it is now known that there are closer to 120-130 million hectares. This difference, of up to 40%, is due to a number of factors. One is that land is not measured in a standard way in much of rural China, but partly by how much it can produce. Also, people are taxed on the amount of land they cultivate so they often hide as much as they can where this is possible. Therefore, in areas near cities, numbers will vary by less than 20%, but in rural areas, they can be off by up to 60%. On average, China's agricultural land grows 1.5 crops per year, with a few areas triple cropping.

Data on rice yields are pretty good, on wheat, fair, and on corn, they are the most uncertain. Actual average corn yield is about four tons per hectare -- about half the U.S. average. Total crop production figures are more accurate than the land figures.

China is now the world's largest producer and user of nitrogen fertilizer, applying almost 20 million tons per year. Roughly two-fifths of this is produced in small coal-based plants. Their product is ammonium bicarbonate, a highly volatile compound with high pre-application and application losses.

Regarding irrigation, there is the key problem of water subsidies. Like Californians, Chinese farmers pay only about one-tenth of the real price of water and so pay little attention to efficient water use. In addition, out of 47 million hectares of irrigated land, only about half is effectively irrigated. Tremendous opportunities to expand production therefore exist in fertilizer and irrigation use. There are major opportunities for improvement in agroecosystem management such as greater use of inter-cropping, water retention methods, etc. There has been a major collapse in the use of traditional ecoefficient ways, and a return to some of these ways could greatly boost production efficiency.

As for the implications of Chinese population growth on world food supply, Smil says that there are other countries to be concerned about in addition to China. Japan is now the world's largest importer of food, self-sufficient only in rice production. Japan, South Korea and Taiwan together now import more than three times as much food and feed grain as China. Chinese per capita meat consumption of 25 kg/year is still only about half that of these other three countries, but as China develops, it will likely dip into the international feed grain market. Further, Smil says that problems of chronic food shortages are more a matter of distribution and access than of food production. In total, there is more food in China than ever, and the country should be able to feed itself for the next two decades.