The Black Death – the pandemic of bubonic plague which swept Europe and Asia for about five years in the mid-1300s – is widely believed to have reduced the global population by one-third.

But almost 700 years after this infamous pandemic became the last worldwide phenomenon to reduce global population levels by such a huge amount, a new report has warned of the “staggering social change” posed by plummeting fertility rates which could also see the number of humans on our planet, currently standing at more than eight billion, fall within decades.

According to a recent global fertility study published in the international medical journal, The Lancet, “Fertility is declining globally, with rates in more than half of all countries and territories in 2021 below replacement level”.

Natalia V Bhattacharjee, one of the report’s co-lead authors, said the “implications are immense” – particularly for countries in Western Europe, which are currently seeing massive unrest over migration levels.

“These future trends in fertility rates and live births will completely reconfigure the global economy and the international balance of power and will necessitate reorganising societies,” she stated.

The study suggested that Western Europe, where the far-right has long made the issue of falling fertility a cause celebre, faces a particularly steep fall in births in the coming decades and may have to reopen itself to unfettered migration to address the problem.

What does the Lancet report say?

The March report, titled, Global fertility in 204 countries and territories, 1950-2021, with forecasts to 2100, (PDF), was compiled by a team of international researchers at the University of Washington’s Institute for Health Metrics and Evaluation (IHME).

It based its predictions on the widely accepted premise that countries require a total fertility rate (TFR) of 2.1 children per woman in order to ensure a broadly stable population.

However, in Western Europe, TFR is forecast to drop from 1.53, where it was in 2021, to 1.44 in 2050, and drop again to 1.37 in 2100, according to the report, which predicts that Spain will suffer one of the steepest declines – to 1.11 in 2100.

The team also predicted that only six countries in the world – Samoa, Somalia, Tonga, Niger, Chad and Tajikistan – would still have a TFR above 2.1 by the turn of the next century.

Why is the birthrate falling?

Falling birthrates, say experts, are the result of greater female participation in the workplace, as well as increased access to contraception. According to bodies such as the UN, more working women make for growing economies.

As macroeconomist Philip Pilkington wrote in a January edition of the UK’s Daily Telegraph: “As wealth in a country increases, its birthrate falls – as surely as night follows day.”

Falling birthrates have also been attributed to advances in medical science meaning that families do not have to produce as many children to ensure enough survive as they might have done in past centuries.

How will this affect Western countries?

If the findings in The Lancet are correct, then the likes of the United Kingdom, where the birthrate is predicted to fall to 1.38 in 2050 and 1.3 in 2100, from 1.49 in 2021, will become reliant on immigration for the next eight decades or more if it is to sustain its population size, currently just under 68 million.

As fewer babies are born and medical advances mean people are living for longer, Western Europe is facing the prospect of a rapidly ageing population. With fewer young people generating wealth to balance the rising costs of sustaining the elderly, countries could face serious economic challenges in the decades ahead.

The Lancet report, which indicated that sub-Saharan Africa would account for one in every two children born in 2100, therefore also predicts that high-income countries will struggle to maintain economic growth.

The only obvious solution, experts say, is to allow more migration from countries with younger populations.

Will countries in the West have to adopt open-border policies?

Eventually, yes, said Bhattacharjee. “Once nearly every country’s population is shrinking, reliance on open immigration will become necessary to sustain economic growth.”.

She added that “sub-Saharan African countries have a vital resource that ageing societies are losing – a youthful population”.

However, notions of an “open immigration” policy are anathema to many of today’s Western democracies.

In the UK, for example, British Prime Minister Rishi Sunak has made curbing immigration a top priority as his Conservative Party government waits for its long-awaited policy of sending asylum seekers to Rwanda to be signed into law.

And in France, President Emmanuel Macron had sought to implement his “hardline” immigration bill after it was passed by the French parliament in December last year. However, in late January, the country’s constitutional court, which examines new laws to ensure they are in keeping with the tenets of the French constitution, struck down large parts of the bill, including a proposal to restrict migrants’ access to welfare benefits, prompting Macron to promulgate a more watered-down version of his bill.

Despite this, many observers contend that the new law still represents a hardening of French immigration rules.

Why is the far-right concerned about falling Western birthrates?

Enthusiasts of the far right have been concerned with the idea of declining birthrates since long before The Lancet published its study.

Indeed, “the Great Replacement” conspiracy theory – which was first popularised by right-wing French philosopher Renaud Camus in his 2011 book, Le Grand Remplacement – promotes the false and racist idea that falling birthrates in Western societies are part of a “plot” which could lead to whites being largely “replaced” by people of other races.

Hungary’s far-right, anti-immigration prime minister, Viktor Orban, has also been accused of tapping into “the Great Replacement” theory in his own bid to advocate for improving birthrates in Europe, including in his own country.

In 2019, the year he announced a series of family-friendly policies in Hungary like housing subsidies in an attempt to drive up birthrates, Orban rejected the notion of 21st-century Europe being “populated by non-Europeans”.

“If Europe is not going to be populated by Europeans in the future and we take this as given, then we are speaking about an exchange of populations, to replace the population of Europeans with others,” he said.