The most obvious environmental impacts are usually local, such as the disappearance of forests and associated watersheds, soil erosion or desertification or the brown haze hovering over cities. Less obvious are phenomena such as the build-up of carbon dioxide in the atmosphere, the global decline of fish catches or the pollution of land and water resources with industrial and hazardous wastes. Further complicating the issue is the lack of data to help researchers determine trends and accurately measure what is happening, a reflection of the relative youth of the environmental sciences, disciplines that require expertise across research areas. Each year, an estimated 5 to 7 million hectares of agricultural lands are lost to accelerating land degradation and rapid urbanization. Another 16 to 20 million hectares of tropical forests and woodlands are lost each year.
Water is a finite resource.
There is no more water on earth now than there was 2,000 years ago when the population was less than 3 per cent of its current size. During this century, while world population has tripled, water withdrawals have increased by over six times. By 2025, close to 3 billion people in 48 countries will be affected by critical water shortages for all or part of the year. The pollution and increasing scarcity of renewable fresh water supplies also threaten human health and welfare. Waterborne diseases infect some 250 million people each year, about 10 million of whom die.