Fires used to clear forest for farmland — a practice known in Portuguese as 'quemadas' — in the Amazon are responsible for three-quarters of Brazil's carbon dioxide emissions. But each hectare of forest absorbs, on average, a half-ton of carbon each year. Meanwhile, the region's rivers emit one to two tons of carbon dioxide per hectare of surface area per year.

These are some of the conclusions reported last week in Brasilia by the Large-Scale Biosphere-Atmosphere (LBA) experiment, a series of studies begun in 1996 and which are revealing the dynamics of the Amazon ecosystems and their climatic effects.

Continued deforestation could lead to desertification of central-south Brazil and the neighboring countries, where rains depend on the humidity coming from the Amazon forests, said LBA expert Antonio Donato Nobre.