As thick smoke spread through the narrow streets of Havana, seeping into homes, schools and shops, Carlos Blanco, a chef, opened his bedroom window to see what was going on. “I saw a mist. But it wasn't mist – it was smoke,” he says, describing the toxic smog emanating from a smouldering mountain of rubbish. As the US oil blockade on Cuba enters its fourth month, choking off most of the island's fuel supplies , growing mounds of waste lie on street corners across Havana.