""To accept such bids runs the risk of turning the debate into a sterile argument about whether or not climate change is a greater risk," Mr Rogers said in the memo, which was sent to Sir David's office in February. "This sort of discussion does not help us achieve our wider policy aims ahead of our G8 presidency [next year]." The move will be seized on by critics of Mr Blair's stance over the Iraq war as further evidence that he is too subservient to the Bush administration. It will also be seen as an attempt to bolster the Prime Minister's case for pre-emptive strikes to combat the threat of international terrorism, which he outlined in a speech on Friday. ... If Sir David were to find himself pushed to decide whether terrorism or climate change was the greater threat, he was supposed to answer: "Both are serious and immediate problems for the world today." But this was not what Sir David said on the Today programme on 9 January when the Science article was published. Asked to explain how he had come to the conclusion that global warming was more serious than terrorism, Sir David replied that his equation was "based on the number of fatalities that have already occurred" - implying that global warming has already killed more people than terrorism.