Agence France-Presse: US Energy Secretary Steven Chu has floated the idea of a carbon emissions tax to fight global warming, in an interview with The New York Times Thursday. During the US presidential campaign, the notion was kept largely on the back burner as candidates were reluctant to promote the idea of costlier energy at a time when gasoline prices were soaring. But since President Barack Obama’s administration took office in January, Congress has been working on setting up a system for …