经济学人官方译文 | 人口统计抹掉了几个亿:联合国下调了人口预测数字

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Demography
人口统计
Missing millions
抹掉了几个亿
The UN revises down its population forecasts
联合国下调了人口预测数字

THE UNITED NATIONS is the world’s most important watcher of human tides. Its demographers have a good record of predicting global population change, although they have made mistakes about individual countries. So it is worth paying attention when the UN revises its figures, as it does every few years. The latest bulletin is especially surprising.
联合国是最重要的人口趋势观测机构。它的人口统计学家对全球人口变化的预测一向较为准确,虽然在个别国家上有过失误。因此联合国每过几年对数据所做的修正值得关注。最新发布的数字尤其令人吃惊。

Recent revisions have sent the projected global population upwards. The one released on June 17th cuts it back. The UN now thinks the world will contain a little over 9.7bn people in 2050 and just under 10.9bn in 2100. The first figure is 37m lower than the UN forecast two years ago. The latter is 309m lower—almost an America’s worth of people revised away.
联合国近些年对全球人口的预测都是向上调整。而6月17日发布的数字却做了下调。它现在认为,2050年世界人口将略多于97亿,到2100年将略少于109亿。相比两年前的预测结果,这两个数字分别被下调了3700万和3.09亿——后者抹去了将近一整个美国的人口。

Birth rates are falling faster than expected in some developing countries. In the late 1980s Kenya had a fertility rate of 6.5, implying a woman could expect to have that many children. Two years ago the UN reckoned Kenya’s fertility rate would drop to 2.1 (the point at which the population sustains itself naturally) only in the late 2070s. Because of new data, it now thinks Kenya will reach that point a decade earlier. Uganda also looks less fecund. A smaller cut to India’s fertility rate has a big effect on the global population forecasts because India has so many people.
在部分发展中国家,出生率正以快于预期的速度下降。上世纪80年代末,肯尼亚的生育率为6.5,即一名妇女预期会生6.5个孩子。两年前,联合国估计肯尼亚的生育率要到本世纪70年代末才会下降到2.1(即人口自然更替水平)。而基于最新的数据,联合国认为该国的生育率会提前10年降落到这个点。乌干达的生育率也被进一步下调。相比之下,对印度生育率的下调幅度更小些,但该国人口众多,因而这一调整给全球人口预测带来了很大的影响。

The UN’s population model assumes that countries with fertility rates well below two will bounce back a little. Even in countries where babies have become rare, most people continue to believe that the ideal family contains two or even three kids. But the recovery keeps failing to happen in some places, so the demographers have changed their forecasts in a second way. They now expect some countries with extremely low birth rates, such as Italy, Japan and South Korea, to stay that way for years. Korea, which has a fertility rate of just 1.1, is now expected to have 30m people in 2100—down from 51m today.
联合国的人口统计模型假定,生育率远低于2的国家会略微反弹。即使在出生率极低的国家,大多数人仍然认为理想的家庭应该有两个、甚至三个孩子。但是,在一些地区,生育率一直都没有回升,因此人口统计学家做出了第二类调整:他们现在预计,意大利、日本和韩国等一些出生率极低的国家在多年内还将继续这种状态。比如,生育率仅为1.1的韩国预计在2100年的人口为3000万,远低于目前的5100万。

Another change has to do with death. Most people are living longer. The biggest improvement is in east and southern Africa, where HIV is being treated better. In America, however, the opioid epidemic has pushed up the death rate, especially for men. The chance of a 15-year-old boy dying by the age of 50 is now higher in America than in Bangladesh. It would be nice if the American forecast, at least, proved to be too pessimistic.
另一个变化与死亡率有关。大多数人都更长寿了。因为艾滋病治疗的改善,非洲的东部和南部地区的寿命提升最为显著。然而,在美国,阿片类药物的滥用推高了死亡率,尤其是男性死亡率。现在,美国15岁男孩在50岁前死亡的几率高于孟加拉国。至少,如果对美国的预测被证明过于悲观了,倒是件好事。

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