The topic has become the mainstay of dystopian science fiction. Our world is afflicted by widespread infertility and childless civilisations are left hovering on the brink of collapse. Children of Men and The Handmaid’s Tale provide perfect examples of these unsettling narratives.

Yet the scenarios outlined in these books and dramatisations may be less fanciful than is first supposed. Indeed, reaction to a study of male infertility, published last week, suggests we may already be hurtling towards such a fate.

According to scientists at the Hebrew University of Jerusalem, sperm counts among men in the west have more than halved in the past 40 years and are currently falling by an average of 1.4% a year. Humanity could soon become extinct, it was claimed by some commentators.

It was a chilling and alarming revelation. Western nations – although not developing countries – appear to be facing disaster. But what could be triggering this decline in sperm? And what can be done to counter it?

Answering these questions turns out to be a lot more awkward than was previously realised, and while the most strident apocalyptic warnings that have followed publication of the Jerusalem study are dismissed by experts, most believe its findings suggest we face a major social and biological problem. Worryingly, there is little evidence that any action is being taken to address the coming crisis.

In fact, there was nothing new in the study, Temporal Trends in Sperm Count, by Hagai Levine and others, which was published in Human Reproduction Update last week. The work was an analysis of more than 100 previous studies in the field, and most reproductive health experts have reacted positively to it. Professor Chris Barratt, at Dundee University, described it as a landmark study “that should ring alarm bells”, while Manchester University’s Professor Daniel Brison said its “shocking” results should act as “a wake-up call to prompt active research in the area”.

Nor are they alone in declaring their worries about declining sperm counts in the west. Earlier this year, the World Health Organisation described current knowledge of male infertility as “very low”, a relative ignorance that has since been acknowledged by the UK Medical Research Council, which has issued a call for scientists to put forward projects in the field for funding. “We are still relatively ignorant about the causes of male infertility, and as a matter of urgency we need to increase, substantially, our research effort into male reproductive health,” said Barratt.

The dangers of this ignorance were highlighted by Professor Richard Sharpe at Edinburgh University – though he was also quick to dismiss the more outlandish claims that current dwindling sperm counts could doom humanity.

“The end of humanity is not approaching,” said Sharpe. “But at the individual level, for affected people, this trend could be tragic. We have no treatments for improving sperm production in infertile men, and we have no idea about what is the cause of the condition. We cannot remedy it. So we are completely hamstrung.”

The problem is particularly urgent in the west, where couples are having families much later in life, he said. In 2014, 52% of all live births in the UK were to mothers aged 30 and over (67% of fathers fell into this age group). However, when a woman reaches the age of 32 her chances of conceiving start to decrease gradually but significantly until, by 40, they have fallen by half. At the same time, more and more men now have sperm counts low enough to impair their fertility.

“This creates a double whammy for fertility in modern western societies,” said Sharpe. “Couples wait until they are over 30 and then find that one or both have reproduction problems. In some cases, they may not discover these problems until they are in their late 30s – by which time they have little time left to take advantage of assisted reproductive techniques such as IVF. Couples like these are more and more likely to end up childless – as mothers get older and sperm counts continue to drop – and that is a tragedy. The problem is that the only effective way to treat infertility caused by a man’s low sperm count is to treat his partner, invasively, using assisted reproductive techniques. That may not always be seen as an acceptable approach. We are sailing into a storm.”

The issue is further complicated because the underlying cause of these declining sperm counts remains a mystery. “Almost every aspect of modern life – from mobile phones to smoking and oral contraceptives [contaminating drinking water] – has been blamed for declining sperm counts, but no convincing evidence has emerged to link any of them to the problem,” said Professor Allan Pacey of Sheffield University.

In addition, there have been criticisms of some of the retrospective studies that suggest dramatic falls in sperm counts. Some of the studies were based on men attending fertility clinics who were therefore more likely to have low sperm counts.

Different techniques were used in different studies to count sperm in samples, and this variation could also have skewed results.

Neither set of these kind of studies was included in the meta-analysis by Levine and his team, however, and for this reason, several scientists – including Pacey – who had remained cautious about the extent of the problem, have said that they are much more convinced by the new work.

“This new analysis has gone a long way to get round the flaws of previous studies, so I am much less sceptical about the reality of declining sperm counts in the west,” Pacey said.

The reality of the problem is also supported by the rise in cases of testicular cancer that has taken place in recent years, he added. This also suggests that problems appear to be occurring as the male foetus develops in the womb. In some way, it is becoming more and more vulnerable to changes in conditions there.

Whether these have come about because of alterations to a mother’s diet, or to the drugs she is taking, or chemicals in the environment and other factors, it is hard to say. And why do men outside the western world appear not to be affected?

Scientists are anxious to find an answer, but are unlikely to do so in the short term, they admit. “We should have funded large epidemiological studies of healthy males 25 years ago and this would – by now – have given us a clear answer one way or the other,” said Pacey.

“Unfortunately, it seems as though we might have to wait another 25 years before we might get to know the real answer.”

This point was backed by Sharpe, who warned that the field is still bedevilled by a lack of research investment. “We need a critical mass of scientists trying to find out what is happening and why it is happening. Unfortunately, we still do not have that. Not enough research is being done. Yet I believe the problem is getting worse.”