Two years ago the UN Population Division said that it expected the world population to grow from 6 billion to 9.3 billion by 2050. It is now expected to reach 8.9 billion.

The forecasters also revised down world growth because people are having fewer babies than expected, with fertility rates declining in much of the developing world. Indian women are now having fewer babies than American women were in the 1950s. Within half a century, fertility in three quarters of developing countries is expected to have fallen below the replacement rate of 2.1 babies per woman.

Thoraya Ahmed Obaid, head of the UN Family Planning Association, welcomed the news: “International efforts in the field of population have been a success. Today, women and men in large numbers are contributing to slower population growth. These decisions are benefiting not only individuals, but also their families, communities and nations.” However, the report gives warning that population growth will accelerate if couples do not continue to have access to family planning. At present, 350 million couples still do not have access to contraception. If fertility levels off rather than continuing to fall world population will reach more than 12.8 billion by 2050.

All the demographic growth will be in the developing world, the population of the developed world remaining steady at about 1.2 billion.

Population growth in the US, Canada, Australia and Britain will be fuelled by two million people emigrating from poor countries to rich ones. Low birth rates will produce a fall in population in most of the rest of the developed world, including much of Europe, and Japan.

Countries in Eastern Europe will see falls in population of up to 50 per cent, as a result of high death rates, low birth rates and emigration. The population of Russia is expected to fall by more than 40 million to 101 million, the figure in 1950.

The only other countries to have declining populations will be the seven in Sub-Saharan Africa that are the most ravaged by Aids. Botswana, where two in every five adults are HIV-positive and life expectancy is 29 years, is expected to lose a fifth of its people by 2050, and South Africa’s population to fall by four million.

At present, more than 40 million people in the world are HIV-positive, and the report suggests that the virus will spread more slowly after 2010 as people modify their behaviour in response to health education. However, it still expects a total of 278 million people to die from developing Aids by 2050.

Despite falling fertility, population growth is expected to continue to be rapid in most of the rest of the developing world. It will be fastest in the very poorest countries, where women still have on average more than five babies. The combined population of Burkina Faso, Mali, Niger, Somalia, Uganda and Yemen is projected to quadruple from 85 million to 369 million.

South Asia is expected to be the most rapidly growing region, with India’s population rising by more than 500 million in the next half century, so that it becomes the world’s most populous country, with 1.53 billion people. Pakistan is expected to grow from 143 million to 349 million, and Bangladesh, already the most densely populated country, to grow from 138 million to 255 million.

Growth in China, which has vigorously enforced its “one child policy”, will be relatively modest, from 1.3 billion now to 1.4 billion in 2025, and then falling gradually.

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