'By what right,' an angry environmentalist demanded at a recent conference I attended, 'do Americans place such a heavy footprint upon God's Earth?' Ouch. That was a tough one because, alas, it's largely true.

We comprise slightly less than 5 per cent of the world's population; but we imbibe 27 per cent of the world's annual oil production, create and consume nearly 30 per cent of its Gross World Product and - get this - spend a full 40 per cent of all the world's defence expenditures. By my calculation, the Pentagon's budget is nowadays roughly equal to the defence expenditures of the next nine or 10 highest defence-spending nations - which has never before happened in history. That is indeed a heavy footprint. How do we explain it to others - and to ourselves? And what, if anything, should we be doing about this?