America's coal, oil and car lobbies have stood in the way of any significant US commitment to reduce carbon dioxide output, and the US is the world's largest emitter of carbon dioxide. Usually there has to be very widespread and very visible environmental damage before action is taken. The thinning of the ozone layer fitted that category well and the response was swift. Global warming is still a long way from the damage being widespread enough, and attributable clearly enough to human activities, for politicians to be ready to speed up the move into renewable energy. The answer is all the more difficult because we usually don't know in advance what is 'in time'.
Many critical changes are subject to threshold effects.
When a certain point is crossed, very sudden and disastrous change can occur with little warning. In many cases we do not know where the thresholds lie. Prudence dictates a preventive approach - a stitch in time saves nine. But the history of environmental problems shows that politicians rarely act decisively until the brink is reached, and it will always be touch and go whether we are pushed over it or not. Please send us cuttings.