World's population estimated to have passed 8 billion

Feeling crowded yet? The US Census Bureau estimates the world's population has topped eight billion for the first time.

The human species has topped eight billion, with longer life spans offsetting fewer births, but world population growth continues a long-term trend of slowing down, the US Census Bureau says.

It estimates the global population exceeded the threshold on September 26, a precise date the agency said to take with a grain of salt.

The United Nations estimated the number was passed 10 months earlier, having declared November 22, 2022, the "Day of Eight Billion", the Census Bureau pointed out in a statement.

The discrepancy is due to countries counting people differently, or not at all. 

Many lack systems to record births and deaths, and populous countries such as India and Nigeria have not conducted censuses in more than a decade.

While world population growth remains brisk, growing from six billion to eight billion since the turn of the millennium, the rate has slowed since doubling between 1960 and 2000. 

People living to older ages account for much of the recent increase. 

The global median age, now 32, is expected to continue to rise towards 39 in 2060.

Countries such as Canada have been ageing with declining older-age mortality, while countries such as Nigeria have seen dramatic declines in deaths of children under five.

Fertility rates, meanwhile, are declining, falling below replacement level in much of the world and contributing to a more than 50-year trend, on average, of slimmer increases in population growth.

The minimum number of such births necessary to replace both the father and mother for neutral world population is 2.1, demographers say. 

Almost three-quarters of people live in countries with fertility rates around or below that level.

Countries with fertility rates around replacement level include India, Tunisia and Argentina.

About 15 per cent of people live in places with fertility rates below replacement level. 

Countries with low fertility rates include Brazil, Mexico, the US and Sweden, while those with very low fertility rates include China, South Korea and Spain.

Israel, Ethiopia and Papua New Guinea rank among countries with fertility rates of up to five. 

Such countries have almost one-quarter of the world's population.

Only about four per cent of the world's population lives in countries with fertility rates above five, and all are in Africa.

Global fertility rates are projected to decline at least through 2060, with no country projected to have a rate higher than four by then, according to the bureau.