Should Congress require any further reason to move aggressively to limit greenhouse gas emissions, it need only read last Friday’s report from the Intergovernmental Panel on Climate Change, the world’s authoritative voice on global warming.

A distillation of the best peer-reviewed science, the report expresses more than 90 per cent certainty that man-made emissions from the burning of fossil fuels have caused the steady rise in atmospheric temperature, with the destruction of tropical rain forests playing a lesser but important role.

Talk is cheap in Washington, while meaningful action is almost certain to be expensive. President Bush has brandished the costs of moving to a new energy-delivery system again and again to argue against mandatory caps on emissions and to make the case for his own cost-free and demonstrably inadequate programme of voluntary reductions. Yet what the panel is telling us is that the costs of doing nothing, especially to future generations, will be far greater than the price of acting now.

This is not a report compiled by a bunch of activists or alarmists. It is a consensus document, the inherently conservative product of three years of study and debate among mainstream scientists from around 150 countries. And in its modesty, it is alarming enough.