Bill Becker of the Presidential Climate Action Project reflected on this in an interesting blog post today, and tried to figure out what the candidates might have said if they had been asked (or, at least, what they might have said if they had stayed consistent with their stated policy positions!)
By the way, despite its official-sounding name, the Presidential Climate Action Project is not an agency of the US government. Its mission is "to develop policy recommendations on climate and energy security, with a focus on what the President of the United States could accomplish using his or her executive authority - in other words, without action by Congress."
Becker begins: "If Mitt Romney and Barack Obama had been able to look through the television cameras at who was watching their first debate, it undoubtedly would have been more interesting than the debate itself."
Read the full post here.