Leading article: Save the lungs of our planet

The resignation of Marina Silva as the Environment minister of Brazil is a blow to the very future of the planet. Five years ago, she was appointed guardian of the Amazon but, in that time, she has fought an uphill battle against the loggers and ranchers of Brazilian agribusiness. Indeed, she often seem a lone voice in the Brazilian government – outvoted on the introduction of genetically-modified grains, on the construction of a new nuclear power plant and on massive infrastructure projects, including two big hydro-electric dams and a major new road in the rainforest. She has finally quit, worn down by ill-health and the appointment of a rival minister to speed the approval of energy projects.

It is easy for rich nations to condemn an emerging economy which succumbs to commercial pressures and abandons the environment. But this is not one country's problem. Climate change is the greatest market failure the world has seen; those who pollute are generally not the ones who pay. The Amazon is a precious resource for the whole world, and one for which we must all take responsibility.

Tropical rainforests are the lungs of the planet. They generate most of the world's rainfall and form a precious cooling band around the Equator which acts as the Earth's thermostat. Photosynthesis makes them a massive absorber of carbon, regulating the global climate. Cutting down these forests causes two problems. It removes that carbon sink. And, since trees are mostly cleared by burning, it sends vast amounts of greenhouse gases into the atmosphere. Almost 25 per cent of the world's total emissions now come from deforestation – far outstripping the 14 per cent produced by planes, cars and factories. Yesterday's deforestation alone released as much carbon dioxide into the air as would eight million people flying from New York to London.

The Stern report, commissioned by the British government, saw curbing deforestation as the single biggest thing we can do to arrest global warming. It is also the cheapest – 30 times cheaper than reducing emissions from fossil fuels – and no new technology is needed. Just the political will and about $80bn, a relatively small bill if it is paid by the whole world. Stern identified what that should be spent on: clarifying forest property rights, strengthening law enforcement and paying from public funds to counter the lure of cash from vested interests. Brazil will not pay. Why should it pay for something that benefits everyone? Working out a viable international agreement is the challenge for the next Kyoto. But one thing is clear. This part of Brazil is too important to leave to the Brazilians. If we lose the forests, we lose the fight against climate change.