The demographic tides now rising in the developed, Western world are well recognised. By now most of us realise that, as more and more of us join the ranks of the elderly in the years ahead, the proportion of the population that remains of working age will steadily dwindle.

In Britain, by 2025 there will be three people of working age for every person aged 65 or more, compared with about four at present. Across much of Europe, many countries will see their populations age even more sharply.

Western governments are being forced to grapple with the negative consequences for growth, competitiveness and productivity, and the fiscal challenges of what will be soaring costs for pension provision and healthcare.

What has scarcely been noticed, however, is that, for much of the developing world, as well as the rich West, the future is also grey.

Across large tracts of Asia, Eastern Europe and parts of the Middle East, in China, Russia and even India, the phenomenon of population ageing has already taken firm hold. And for these countries, the challenges posed are greatly magnified by their relatively low income levels.

The startling demographic shifts taking place in much of the developing world have been highlighted in a compelling analysis for the World Economic Forum (WEF) by Nicholas Eberstadt, of the American Enterprise Institute, the Washington think-tank.

While much crystal-ball gazing about political and economic trends is notoriously subjective, Mr Eberstadt notes that the unforgiving ageing process makes the demographic fates of developing and emerging-market countries quite easy to divine.

By 2025, projections from United Nations and the US Census Bureau indicate that the world population will have reached 6.7 billion people, two thirds of whom have already been born.

Over the coming two decades, the population of the developing world is set to rise by a quarter, with the most rapidly growing age group being those aged 65-plus. The implication is that the number of senior citizens in these countries will roughly double to 570 million by 2025, or 8.5 per cent of their combined populations.

One of the curious factors brought out by the WEF’s study is that the driving force behind these trends is not lifespans but birth-rates.

Probably contrary to much popular wisdom, the root cause of population ageing is not that people are necessarily living longer, but that the developed and much of the developing world is less fertile, with what demographers call “sub-replacement” birth rates — rates so low that ultimately they would result in a smaller overall population. It may come as a surprise to many that these conditions already prevail in much of Asia, Latin America and India, as well as in China, with its notorious coercive system of population control.

The predicament now confronting the nations concerned, many of them key emerging markets, is that rapid ageing is taking hold at a time when their income levels are far below those enjoyed by developed countries as they faced similar population shifts.

As the report spells out, China had about the same proportion of people aged 65-plus in 2000 as Japan did in 1970. But at that time Japan enjoyed incomes per head three times those prevailing in China at the start of this decade.

Similarly, Russia’s incomes per head in 2000 were a sixth of those enjoyed in the United States when it had a similar proportion of elderly.

Mr Eberstadt draws a grim picture of the potential social and economic repercussions.

In China, for example, the population of elderly people is set to rise at a rate of about 3.5 per cent a year. Those aged 65 or over will double in number to 200 million or so over the next two decades.

By 2025, in some provinces of the country, such as the poor Heilongjiang area, the 65-plus cohort could account for as much as a fifth of the population, and the average age could top 50. Yet Heilongjiang’s people had an annual income per head of just $1,100 in 2001.

With China’s existing state pension system covering only a sixth of the workforce and already saddled with unfunded liabilities worth more than the country’s GDP, the WEF’s analysis suggests that many elderly Chinese will be forced to fall back on family support. Yet the extent of that support is also in doubt, with China’s population control having led to so-called “son deficit”. By 2025, it is estimated that a third or more of retiring Chinese women will have no living sons, who traditionally have the duty of supporting elderly parents.

Mr Eberstadt suggests that what he calls a “slow motion humanitarian tragedy” may already be under way, with tens of millions of ageing and low-skilled rural Chinese citizens facing the prospect of being left to support themselves through demanding physical labour, often in the fields, even in the face of ill-health and disability.

In Russia, the WEF study suggests that the problems of an ageing population will be compounded by the ill-health that plagues Russians of all ages, leaving growing numbers of the elderly reliant on a shrinking and sickly, low- income workforce.

In India, too, the absence of a viable national pension system poses enormous challenges. The report finds that the nation is facing a demographic divide between a youthful but poor and still ill-educated north, and an ageing if more prosperous south, where 9 per cent of people are expected to be 65 or over by 2025.

These are sobering scenarios for greying Westerners as we fret over retirement prospects amid national pensions crises. Our rich nations have the means, at least, to tackle the consequences of our ageing populations. We may yet look at the fortunes of the elderly poor elsewhere and count our blessings.

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