he overall forecast for tonight and the next 15,000 days — up to the year 2050 — is for persistent demographic accumulation, especially in urban areas in the global south, declining levels of reproduction, widespread aging, continuing broad bands of migration streams and scattered mortality disturbances.

Turning to the details, the world is now at an all-time high of 6.7 billion people. The six billion mark was set in 1999, only 12 years after the earlier high of five billion in 1987. The current level of accumulation is 78 million people per year. This is lower than the record annual high of 89 million set in the late 1980s. The seven billion mark is expected to be reached in about 1,500 days, in 2011. The current global forecast for mid-century is about nine billion people, but also possible is a high of 11 billion — or a low of eight billion.

The planet’s human population is growing at 1.2% per year, markedly lower than the all-time record high of 2.0% set back in the 1960s. A more detailed look across the map shows great variability, regionally and nationally — as well as significant demographic turbulence and instability in some areas. Nearly all of the demographic accumulation during the coming 15,000 days — about 2.5 billion people — is expected to occur among the less-developed regions. This accumulation amounts to a 50% increase by mid-century, with some areas, especially in Africa, expected to experience even higher levels of accumulation.

Today, six countries — India, China, Pakistan, Nigeria, Bangladesh and Indonesia — account for half of the world’s yearly demographic accumulation. India’s annual accumulation — one-fifth of global growth — is equal to the combined totals for China, Pakistan and Nigeria. Most of the more-developed regions, in contrast, will see little if any demographic accumulation. The population of the European continent peaked several years ago and is now declining. And many places, such as Italy, Germany, Japan and Russia, are experiencing — or will experience — demographic shortfalls.

The forecast is for Europe’s population to be 10% smaller by mid-century, with the working-age population likely experiencing a 25% decline. About the same is expected in East Asia for countries such as Japan, Singapore and the Republic of Korea. However, areas of notable exception to these demographic shortfalls are Australia, Canada and the United States, where demographic accumulations of 30-40% are expected by the end of the forecast period, due in large part to continuing high streams of migration.

A depressed low fertility system covers close to half of the world’s population, with European countries and Japan experiencing the lowest recorded fertility levels, at 1.1 to 1.5 births per woman. While fertility highs remain in most of Africa and parts of Western and South Asia, these levels are falling, especially in urban areas. By the end of the 15,000-day forecast, global fertility is expected to hover around the replacement rate.

Global improvements in mortality are expected to continue, with more people reaching advanced ages. However, scattered mortality disturbances, heavy at times, will occur mainly in Africa and Asia, with isolated disturbances in Eastern Europe. A rapidly moving, high-pressure HIV/AIDS epidemic is causing a mortality tsunami, ravaging much of sub-Saharan Africa and some parts of South and East Asia.

Broad bands of migration streams, with many immigrants entering or remaining illegally, will persist and possibly intensify. The streams are moving primarily from the south in a northerly direction and also from east to west. In addition, there will be continued migration activity within countries, with many seeking shelter in large cities, especially along the warmer seacoasts.

s a result of lower fertility and longer lifespans, a widespread aging front is rapidly sweeping across the globe. This front, beginning in Europe and travelling from west to east, will result in extraordinary shifts in age structures towards elevated ages. The numbers and proportions of elderly will likely reach historically unprecedented high levels. In many areas, one person out of three is expected to be over age 65 — and the number of persons of working age per one older person will fall sharply, from the current level of about four to two or fewer by mid-century.

These shifts in age structures will exert seismic pressures on social, economic and political conditions in all countries and areas, especially in the north. The pressures from this aging front are expected to precipitate political squalls and produce unpleasant conditions for many localities and government bodies.

It should be noted that the broad migration streams noted earlier are not expected to eliminate the pressures from the enormous and rapidly expanding aging front.

For some areas, replacement migration can offset forecasted declines in the size of overall populations — and of working-age populations. However, replacement migration cannot realistically offset population aging because the numbers involved are simply far too high.

The extended long-term forecast for the next 15,000 days remains unsettled. While the outlook for some areas is partly sunny and pleasant, unstable and uncomfortable conditions are expected to persist in many regions and localities.

Troubling scattered clouds are also forming on the horizon due to intensifying aging, mortality disturbances and migration streams.

Joseph Chamie is the director of research at the Center for Migration Studies in New York City.

Last updated September 17, 2009