Business Green: Google has unveiled a $4 trillion plan detailing how it thinks the US should transition to a low carbon economy. The wide-reaching strategy sets out a series of proposals designed to wean the United States’s energy network off coal and oil by 2030 and cut cars’ use of fossil fuels by 40 per cent by the same date. “It’s cheaper to fix global warming than to ignore it,” said chief executive Eric Scmidt at the unveiling of the new strategy. “The payback on energy efficiency is …