7 billion, 7 billion and 1,7 billion and 2-and counting

摘要

October 31st 2011 was the day the world's population reached 7 billion. Officially. The UN has calculated it, so it must be true. Up to a point, at least. The US Census Bureau has done its own calculations, and they reckon the world's seven billionth child will not be born until February 2012. Wolfgang Lutz, of the World Population Program in Laxenburg, Austria, differs again: he thinks we still have almost a year to go before the seven billionth happy event. The disagreements should not be terribly surprising, given that small changes in birth rates and death rates act cumulatively, that censuses generally take place only every ten years or so and even then miss lots of people out, and that Afghanistan, for example, has not had a census since 1979, so who knows what its population might be?