SH: If the Amazon Basin were in the United States it would begin in the Californian Sierras and end in New York. It is the largest expanse of tropical rain forest in the world. Last year the Brazilian Space Institute indicated some 12 million acres were on fire and some 50 million acres had been cleared. Clearing rates are now approaching the exponential. The problem is that these forests are not being replaced by any kind of stable land use, since sooner or later these lands end up as pasture in the hands of a small number of landowners. So you have processes of destruction that are quite sharp, but also processes of concentration that are extremely sharp.

The crucial thing to realize is that you can’t just say, ‘Oh the poor trees—if only we could get a better policy to stop it.’ There’s real money being made, real people displaced, and real resistance movements are opposing what’s going on. It’s a frontier area, and things are worked out under the law of the strongest, or, if you will, the law of the jungle.

None, really. A mature forest respires—that is, uses oxygen—and also produces it, so production and consumption of oxygen are more or less in equilibrium. If you cut the forest down and permit younger growth, you actually get more oxygen, since its rate of production of oxygen is greater than its consumption. So the ‘oxygen loss’ theory is wrong, and people should drop it. What is true is something worse. Take last year, when sixteen million acres were deliberately burned. An extraordinary amount of carbon was released into the atmosphere, and what that can result in, of course, is the greenhouse effect. The magnitude of carbon-dioxide increase, just from what’s been going on in the Amazon, is almost twentyfive per cent of global additions.

Another climatic glitch pertains to the cycling of rainfall by the forest. Radioisotope techniques have established that about half of the atmospheric water in Amazonia comes via wind from the Atlantic Ocean, while the other half is from vapour recycled by the trees themselves. So a change in the forest cover will alter the amount of moisture circulating into the atmosphere, and this may already be having a serious effect on climate in adjacent regions outside the Amazon. These general climatic effects are hotly debated, and most projections are still being worked out at the level of modeling. But even so, the initial results are rather disturbing.

There’s the question of genetic diversity. The Amazon forest is the single richest in species diversity, being home to more than two million species, and as you cut down forest with reckless abandon you certainly lose species, even if we can’t document when or where. It’s difficult to put a value on what ‘unknown’ species might be worth. After all, a hundred years ago rubber was just another tree in the jungle that produced an uninteresting latex, but that changed overnight with the Industrial Revolution and Mr Goodyear. One in every six prescription drugs we use has a tropical source for its active chemicals; while indigenous people use eighty per cent or more of the species in a given area for everything from birth control to witchcraft, our science recognizes, but still hasn’t documented, their significance in terms of medicine, food, forage and so on. There are still a lot of unstudied chemically active plants out there, and what has no value today could be precious in the future. But even if it has no value, why burn off the diversity of the world for no good reason?