Why should we care about people who are not yet born? If climate change destroys the lives of people two or three generations down the line, so what? Well, bear with me, here’s a possible answer. And it involves a thought experiment — one proposed by the American philosopher Samuel Scheffler but inspired by a work of fiction.

We normally take two basic facts for granted. We take it for granted that one day we will die —that we’re mortal. And we take it for granted that although we ourselves will die, other people will go on living. But suppose you knew that after your death the human race would soon die out. Perhaps for some reason humans had become infertile, the plot line for P D James’ novel, The Children of Men. In other words, imagine that people who are alive today, including your children and grandchildren, would live out their natural lives — but no new people would appear.

How would that make you feel? What would that do to how you live your life? Would it make any difference to the projects that you currently pursue?

Samuel Scheffler thinks that most of us would regard the imminent end of humanity as a catastrophe. He’s spoken to so many audiences about this that he has empirical evidence to back up this hunch. And if we really believed humans would cease to exist soon after our deaths, he says, it would affect almost everything we do.

Most obviously, projects whose aim is to benefit people in the future will seem pretty futile: the scientist working on a cure for diabetes, the urban planner imagining new ways to lay out cities, the educationalist researching how kids can most effectively learn. All that could seem a waste of time.

But Scheffler believes that the knowledge that humans would soon cease to exist would also touch activities that seem to have nothing to do with the future. It would undermine the satisfaction we take even in things like sex, music, and sport, he says.

Take sport. Would you not continue to take pleasure in the football season? Well, perhaps not . Suppose you support Tottenham and each year you ardently want them to win the Premier League. That desire only makes sense in a historical context — the history of the league and its ongoing future. It’s not at all obvious that if you believed the league would soon cease to exist, because players would soon cease to exist, that you would support Tottenham with the same enthusiasm or intensity.

What does all this show? Scheffler draws several important conclusions, but one of them is as follows. Usually, when we worry about what kind of planet we’ll bequeath to our descendants the issue is couched in terms of the obligations of our generation. That is to say, although it is a burden to have to take future people into account, nonetheless we have a moral duty to do so.

But Scheffler’s thought experiment turns the ethical burden on its head. True, future people need us not to mess with the planet. But it turns out that we need future people as much as they need us. And that puts the relationship between us and our descendants in a wholly different light.

Samuel Scheffler did not need to discover philosophy, he grew up with it. His paternal grandparents were from Romania, his maternal grandparents from Poland, but his father was Israel Scheffler, a Harvard philosopher. Israel was also an ordained Conservative rabbi and Sam was raised in “a fairly observant household”. Asked about his Jewish identity he offered a wonderfully philosophical reply. “My Jewish identity consists partly in the fact that I spend a lot of time thinking about what my Jewish identity consists in, though it is no less strong for that.”