Economist: THE Amazon’s dry season, from July to September, is when the grileiros cut and burn the rainforest. The smoke is so thick it can be seen from space. It also stops rainclouds forming, so the flames burn higher. But on a recent surveillance flight over the forest frontier in Brazil’s state of Pará, there was hardly a wisp of smoke in the sky. Even the people from Greenpeace, whose flight this was, were impressed. They can take some credit, thanks to their Amazon beef campaign. But even …