Devoid of American participation, the international market in carbon dioxide emissions is a partly formed creature whose health remains uncertain. When President George W. Bush took office he refused to ratify the United Nations’ Kyoto protocol on climate change and attempts to set up a domestic system of trading emissions have been thwarted.

But with Mr Bush’s departure next January, that is likely to change. Both John McCain and Barack Obama have pledged to introduce a federal carbon trading system if they succeed him. Though a proposal for such a system failed to secure enough support for a vote in the Senate this month, many think it will return successfully under a new administration.