The thinning of the ozone layer fitted that category well and the response was swift. Global warming is still 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. 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 thres- holds 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.