Economist: IT IS what passes for a winter’s day in upstate São Paulo. The sun is blazing from a blue sky feathered lightly with cirrus cloud. In a large, sloping field overlooking the city of Piracicaba, a mechanical harvester chomps through a stand of three-metre-high sugar cane, fat and juicy from months of sunshine. The harvester slices the cane into 20cm chunks and regurgitates them into a 30-tonne trailer moving alongside that will lug them a few kilometres to the Costa Pinto mill (pictured). …