The consequences would be truly awesome. The wet Amazon, the planet's greatest celebration of life, would turn to dry savannah at best, desert at worst. This would cause much of the world - including Europe - to become hotter and drier, making this sweltering summer a mild foretaste of what is to come. In the longer term, it could make global warming spiral out of control, eventually making the world uninhabitable.

The force that is pushing both the Amazon and the world to the brink of disaster is deforestation. In the past three years, nearly 70,000 square kilometres of the Amazon rainforest have been destroyed. The felling is both drying up the entire forest and helping to cause the hurricanes that have been battering the United States and the Caribbean.

The hot, wet Amazon, normally evaporates vast amounts of water, which rise high into the air as if in an invisible chimney. This draws in the wet north-East trade winds, which have picked up moisture from the Atlantic. This in turn controls the temperature of the ocean; as the trade winds pick up the moisture, the warm water that is left gets saltier and sinks. Deforestation disrupts the cycle by weakening the Amazonian evaporation which drives the whole process. One result is that the hot water in the Atlantic stays on the surface and fuels the hurricanes. Another is that less moisture arrives on the trade winds, intensifying drought in the forest.

The main reason behind the destruction of the Amazon is the production of Soya beans. The protein-rich bean has become a profitable link in the processed food chain and 80 per cent of world production is fed to livestock. Brazilian soya beans are feeding Europe's growing hunger for cheap meat substitutes, and have overtaken logging and cattle ranching as the main engine of deforestation.

Huge soya farms financed by Cargill, the largest privately owned company in the world, represent the worst of rapacious capitalism. The family-owned behemoth, with a turnover of more than $7bn (?3.8bn), is the undisputed ruler of the global grain trade. It also owns British-based Sun Valley foods, which processes a million chickens a week into fresh and frozen, supermarket wrapped products. Its major clients are McDonald's and the Morrisons chain.

I appeal to you to think very carefully about what you buy the next time you go shopping or want some fastfood.