China's population is presently estimated to be 1.38 billion, and India's at 1.31 billion.

© 2015, The New York Times News Service

Demographers have known for some time that the number of people in India would surpass the number in China, the two most populous countries in the world. But they did not anticipate that the change would happen so quickly.The United Nations reported Wednesday that India's population will probably surpass China's by 2022, not 2028, as the organization had forecast just two years ago.In its 2015 revision report, the population division of the U.N. Department of Economic and Social Affairs said China's population was now 1.38 billion, compared with 1.31 billion in India. But in seven years, the populations of both are expected to reach 1.4 billion.Thereafter, the report said, India's population will grow for decades, to 1.5 billion in 2030 and 1.7 billion in 2050, while China's is expected to remain fairly constant until the 2030s, when it is expected to slightly decrease.Overall, the report said, the world's current population of 7.3 billion is expected to reach 9.7 billion by 2050, slightly more than the 9.6 billion forecast two years ago. The number could reach 11.2 billion by the end of the century.Much of the overall increase between now and 2050 is expected in high-fertility countries, mainly in Africa, or in countries with large populations, the report said.Half the growth is expected to be concentrated in just nine countries: India, Nigeria, Pakistan, the Democratic Republic of Congo, Ethiopia, Tanzania, the United States, Indonesia and Uganda.By contrast, the populations of 48 countries are expected to decline in that period, mainly in Europe, because of a slowdown in fertility rates that started decades ago. The report said several countries faced a population decline of more than 15 percent by 2050, including Bosnia and Herzegovina, Bulgaria, Croatia, Hungary, Japan, Latvia, Lithuania, Moldova, Romania, Serbia and Ukraine.Among the 10 largest countries by population, one is in Africa (Nigeria), five are in Asia (Bangladesh, China, India, Indonesia and Pakistan), two are in Latin America (Brazil and Mexico), one is in North America (the United States), and one is in Europe (Russia). Among these, Nigeria's population, currently ranked seventh largest, is growing the fastest, and it is expected to surpass the population of the United States by 2050, which would make it the world's third most populous country.The population revision report also included some notable findings on aging. The number of people 80 or older is projected to more than triple by 2050 and increase more than sevenfold by 2100, the report said. In 2015, 28 percent of all people 80 and older lived in Europe, but that share is expected to decline to 16 percent in 2050 and to 9 percent by 2100, as the populations of other areas increase in size and grow older.The revision report confirmed that substantial improvements in life expectancy have been made in recent years.Globally, life expectancy has risen to 68 years for men and 73 years for women in 2010-15, from 65 years for men and 69 years for women in 2000-05.The highest levels of life expectancy in 2010-2015 are in China, followed by Japan, Italy, Switzerland, Singapore, Iceland, Spain, Australia and Israel, in that order.Globally, the report said, life expectancy is projected to rise to 77 years in 2045-50 and 83 years in 2095-2100, from 70 years in 2010-2015.The population estimates and projections from the United Nations are an important benchmark for global trends, as well as for helping provide demographic data to calculate many other important indicators, including health data, around the world.