Predicting the fate of the Earth has long been a gloomy business, a profession where bad things only seem to get worse over time. From books like "The Population Bomb" to "The End of Nature," ecological pundits of the past 40 years have forecast a dark future of pollution, extinction and growing health problems. But, as the 20th century comes to a close, some leading researchers and policy-makers see evidence that the world's environmental tide may be about to turn. If people continue destroying the environment , the world won't be as perfec ....