Economist: NO ONE really knows how fast global warming will make the oceans rise. But what is clear is that south-east Louisiana is sinking, rather rapidly by geological standards. Add in the prevalence of hurricanes in the neighbourhood, and it becomes a dangerous place to live. Land subsidence in the Mississippi delta is largely caused by human interference. When the river was allowed to flood over its banks every year, some of the muck that spilled out remained, creating more and higher land …