Predictions of the collapse of the tropical rain forests have been around for years. Yet until recently the worst forecasts were almost exclusively linked to direct human predation, such as clear-cutting and burning for pastures or farms. Some scientists believe that the rise in carbon levels means that the Amazon and other rain forests in Asia and Africa may go from being assets in the battle against rising temperatures to liabilities. Amazon flora, for instance, holds more than 100 billion metric tons of carbon, equal to 15 years of tailpipe and smokestack emissions. If the collapse of the rain forests speeds up dramatically, it could eventually release 3.5 billion to 5 billion metric tons of carbon into the atmosphere each year—making forests the leading source of greenhouse gases.

　　有关热带雨林毁灭的预测已经有好多年了。然而直到最近，最坏的预测几乎都与人类的破坏相关，例如为建牧场或农场而成片砍伐和焚烧森林。一些科学家相信，二氧化碳水平的升高意味着亚马逊和亚洲、非洲的雨林可能从用以对抗温度升高的财富变成债务。例如，亚马逊植物群含有一千多亿吨的二氧化碳，相当于排气管和烟囱15年的排放量。如果雨林毁灭的速度大幅加剧，每年将向大气释放35亿到50亿吨的二氧化碳，成为温室气体的主要来源。