Small countries often lead where giants lumber behind, and Guyana's offer of its rainforests to global stewardship is a good example (Report, 27 March). This is vital, for we now realise that industrial-strength deforestation in the tropics is a deadly factor in global warming, and, at last, there may be serious money available to prevent it. But after 20 years working on tropical conservation, I've seen that money alone can't buy it. The forces that destroy forests have huge momentum, and can obliterate ecosystems even when governments and financiers wish otherwise. To oppose this danger, millions of people are needed, their eyes alert to the tell-tale signs of forest invasions, their mobile phones reporting fires and logging roads, their votes and actions demanding enforcement and compliance. With everyone a citizen scientist, illegal logging, farming and ranching, which thrive in darkness and corruption, can be made to shrivel in the light. Everyone can help by observing, investigating, and reporting. This is the great challenge of our times. Your biosphere needs you!