"People are saying that they want be convinced [about global warming], perfectly. They want to know the climate science projections with 100 per cent certainty. Well, we know a great deal and even with that there is still uncertainty. But the trend line is very clear. We never have 100 per cent certainty. We never have it. If you wait till you have 100 per cent certainty, something bad is going to happen on the battlefield. That's something we know. You have to act with incomplete information. You have to act based on the trend line."