The United Nations forecast Thursday that the world's population will increase from 7.2 billion today to 8.1 billion in 2025, with most growth in developing countries and more than half in Africa. By 2050, it will reach 9.6 billion.

India's population is expected to surpass China's around 2028 when both countries will have populations of around 1.45 billion, according to the report on "World Population Prospects." While India's population is forecast to grow to around 1.6 billion and then slowly decline to 1.5 billion in 2100, China's is expected to start decreasing after 2030, possibly falling to 1.1 billion in 2100, it said.

The report found global fertility rates are falling rapidly, though not nearly fast enough to avoid a significant population jump over the next decades. In fact, the U.N. revised its population projection upward since its last report two years ago, mostly due to higher fertility projections in the countries with the most children per women. The previous projection had the global population reaching 9.3 billion people in 2050.

John Wilmoth, director of the Population Division in the U.N.'s Department of Economic and Social Affairs, said the projected population increase will pose challenges but is not necessarily cause for alarm. Rather, he said, the worry is for countries on opposite sides of two extremes: Countries, mostly poor ones, whose populations are growing too quickly, and wealthier ones where the populations is aging and decreasing.

"The world has had a great experience of dealing with rapid population growth," Wilmoth said at a news conference. "World population doubled between 1960 and 2000, roughly. World food supply more than doubled over that time period."

"The problem is more one of extremes," he added. "The main story is to avoid the extreme of either rapid growth due to high fertility or rapid population aging and potential decline due to very low fertility."

Among the fastest-growing countries is Nigeria, whose population is expected to surpass the U.S. population before the middle of the century and could start to rival China as the second-most populous country in the world by the end of the century, according to the report. By 2050, Nigeria's population is expected to reach more than 440 million people, compared to about 400 million for the U.S. The oil-rich African country's population is forecast to be nearly 914 million by 2100.

The report found that most countries with very high levels of fertility — more than 5 children per women — are on the U.N. list of least-developed countries. Most are in Africa, but they also include Afghanistan and East Timor.

But the average number of children per woman has swiftly declined in several large countries, including China, India, Indonesia, Iran, Brazil and South Africa, leading to a reduction in population growth rates in much of the developing world.

In contrast, many European and eastern Asia countries have very low fertility levels.

"As a result, these populations are aging rapidly and face challenges in providing care and support to their growing ranks of older persons," Wilmoth said.

Wilmoth cautioned that "there is a great deal of uncertainty about population trends." He said projections could change based on the trajectories of three major components — fertility, mortality and migration.

Still, population growth until 2050 is all but inevitable.

The U.N. uses the "medium-variant" projection, which assumes a substantial reduction in the fertility levels of intermediate- and high-fertility countries in the coming years. In the "high-variant" — if women on average had an extra half of a child — the world population would reach 10.9 billion in 2050. In the "low-variant" — if women on average had half a child fewer — the population would be 8.3 billion in 2050.

Among the notable findings in the report:

• The population in developing regions is projected to increase from 5.9 billion in 2013 to 8.2 billion in 2050. In contrast, the population of developed countries is expected to remain largely unchanged during that period, at around 1.3 billion people.

• Africa's population could increase from 1.1 billion today to 2.4 billion in 2050, and potentially to 4.2 billion by 2100.

• The number of children in less-developed regions is at all time high at 1.7 billion. In those regions, children under age 15 account for 26% of the population. In the poorest countries, children constitute 40% of their populations, posing huge challenges for providing education and employment.

• In wealthier regions, by contrast, children account for 16% of the population. In developed countries as a whole, the number of older people has already surpassed the number of children, and by 2050 the number of older people will be nearly twice the number of children.

• Low-fertility countries now include all of Europe except Iceland plus 19 countries in Asia, 17 in the Americas, two in Africa and one in Oceania.

据美联社报道，联合国6月13日最新报告预计，世界人口到2025年将从72亿增长至81亿，到2050年世界人口将达96亿。

印度将为第一人口大国

联合国《世界人口展望》报告称，印度人口有望在2028年左右赶超中国，届时两国人口均在14.5亿左右。报告还预测，印度人口增长到16亿后开始逐渐减少，2100年降至15亿；中国在2030年后人口开始减少，2100年可能降至11亿。

报告发现，虽然全球生育率下降迅速，但依然无法阻止今后十年人口的大幅增加。事实上，联合国已经修订了两年前的人口预测报告。此前，联合国预计的2050年世界人口是93亿。

联合国经济和社会事务部人口司司长约翰•威尔莫斯说，人口增长给世界带来了挑战，但无需恐慌。但有两个极端的情况值得担忧：贫困国家人口增长过快，而富裕国家人口正在下降和趋于老龄化。

“关于如何应对人口急剧增长，现有的世界经验丰富，”威尔莫斯在新闻发布会上说道。“世界人口在1960年至2000年约翻了一番，而这期间世界食物供应增长了两倍以上。”

“问题更多在于极端状况”他补充道。“一是因高生育率而导致人口快速增长，一是由于急剧人口老龄化和极低生育率导致人口潜在下降。”

尼日利亚人口将超美国

报告称，尼日利亚是全球人口增长最快的国家之一，其人口有望在本世纪中叶前超过美国，在本世纪末将与中国争夺世界第二人口大国席位。2050年美国人口将达4亿左右，与之相比尼日利亚人口将高达4.4亿。据估计，2100年非洲富油国人口将接近9.14亿。

报告发现，大部分生育率极高的国家都是联合国所列的最不发达国家，以非洲国家为主，不过也包括阿富汗和东帝汶，平均每个妇女生育的孩子超过五个。

但是，一些大国的生育率却下降迅速，包括中国、印度、印度尼西亚、伊朗、巴西和南非，导致许多发展中国家人口增长率下降。

相比之下，很多欧洲国家和东亚国家生育率极低。“因此，这些国家正加速人口老龄化，面临为越来越多的老年人提供养老保障的挑战。”威尔莫斯说。

威尔莫斯提醒道， “人口趋势有很大的不确定性”，可能会因影响人口的三大要素——生育、死亡和迁移——的改变而变化。不过，世界人口将在2050年之前一直保持增长几乎不可避免。

联合国采用了“中等水平变量（medium-variant）”预计方法，该方法假定中高生育率国家在接下来几年里生育率将大幅下降。而用“高水平变量”法——即平均每个妇女的生育数比中等多0.5 ——2050年的世界人口将达109亿。用“低水平变量”法——平均每个妇女的生育数比中等少0.5——2050年的世界人口将是83亿。

报告中值得注意的数据：

•发展中地区的人口预计将从2013年的59亿增加至2050年的82亿。相反，发达国家的人口在这段时期基本保持在13亿左右不变。

•非洲人口可能从现在的11亿增加至2050年的24亿，2100年可能达42亿。

•欠发达地区的儿童数量在17亿居高不下。15岁以下的孩子占这些地区总人口的26%。在最贫穷的国家，儿童占总人口的40%，为教育和就业带来巨大的挑战。

•富裕地区恰恰相反，儿童占总人口的16%。发达国家总的来说老年人数已经超过儿童数，而且到2050年老年人数将接近儿童数的两倍。

•目前，低生育率国家包括除冰岛之外的所有欧洲国家，外加亚洲19国，美洲17国，非洲2国和大洋洲1国。

•一些国家的人口到2050年预期将减少15%，包括白俄罗斯、保加利亚、克罗地亚、古巴、格鲁吉亚、拉脱维亚、立陶宛、摩尔多瓦、罗马尼亚、俄罗斯、塞尔维亚和乌克兰。

•世界预期寿命有了整体提升，从1950-55的47岁升至2005-2010的60岁，预计2045-2050年达76岁，2095-2100年达82岁。

• The populations of several countries are expected to decline by more than 15% by 2050, including Belarus, Bulgaria, Croatia, Cuba, Georgia, Latvia, Lithuania, Republic of Moldova, Romania, Russia Serbia, and Ukraine.

• Life expectancy at birth for the world as a whole rose from 47 years in 1950-55 to 69 years in 2005-2010 and is projected to reach 76 years in 2045-2050 and 82 years in 2095-2100.