What's our duty to future generations? Greta Thunberg demands an answer

We know the planet is warming. We know we're causing it. We know it will result in drought, plague, famine, disease, drowned coastlines, mass extinctions.

But we also know that many of the worst of these outcomes will be borne not by ourselves - and not even by our children and grandchildren - but by distant generations, still to come, who will inherit the Earth from us in whichever state we care to leave it.

What is the moral relevance of time? Does someone born in 2119 count any less than someone who is alive right now? If so: why? If not: what do we owe these future people, and at what cost to ourselves?

Does it matter that we'll never meet them, or that they can never do anything for us? Can we assume that they will be richer and more technologically advanced than we are now? Does it make any difference that they have no fixed identities, or that who they will be, and whether they will exist at all, depends on our actions and decisions?

Philosophers have long pondered these questions, but for the first time - faced with our complicity in an increasingly uninhabitable earth, and our narrowing window in which to evade it - they are coming to have urgent public resonance.

Non-specialists first became aware of what was happening to the climate in the 1990s. At that time, among these unknown "future people" was one Greta Thunberg.

A girl who would be born in Sweden in 2003; who would first hear about climate change when she was eight; who would find this revelation so horrifying that she would descend into a year-long depression; who would be diagnosed with Asperger's syndrome; who would renounce air travel and overconsumption and animal products; who would leave school to strike outside the Swedish parliament to demand more political action; and who has now, just one year later, become one of the most powerful environmental activists in the world.

Last month she travelled by sailboat to the UN Climate Summit in New York, and there, suppressing tears, declared: "The young people are starting to understand your betrayal. The eyes of all future generations are upon you, and if you choose to fail us, I say we will never forgive you."

Her accusations have been variously received. In the laughing and clapping at the UN address you sense both condescension and relish: that she's providing some a yearned-for rebuke.

She's been called a puppet, and she's been claimed as a mascot. She's been attacked by right-wing media in the US (dismissed as "a mentally ill Swedish child" and compared to Stephen King's Children of the Corn), and she's been hailed as "the Joan of Arc of climate change".

To her credit she seems indifferent to the approving and disapproving alike. Though the saviour narrative gets to her: "You come to young people for hope. How dare you?"

Thunberg will be 17 in a few months, but an important part of her power is in coming across as much younger than she is.

She looks about 10 (her small frame a consequence, reportedly, of the eating disorder that emerged during her battle with depression), and her manner is closer to that of a prodigy than the traits we'd associate with the teens of Generation Z.

Her rhetoric regularly invokes the moral categories (or even caricatures) of "the child" and "the adult": what each role should entail, and how unfairly they have been reversed in our present crisis.

"You're acting like spoiled, irresponsible children," she told the European Economic and Social Committee. Or, on another occasion: "You're not mature enough to tell it like it is. Even that burden you leave to your children."

We are born in a state of innocence - subject to the world as it is - but at some point, this precious coat wears through. Our innocence turns into a sort of participation, and our participation turns into a sort of endorsement. We stop being in a world that is unjust, unequal and cruel, and we become part of that injustice, inequality and cruelty.

No small part of Thunberg's message, and the discomfort of receiving it, is this accusation that our innocence with regard to climate change has now passed: we have known too much for too long, and we have done nothing about it.

Indeed, since the dawning of our awareness - in just a few decades - we have added more carbon to the atmosphere than in all the accumulated millennia before. As climate-change journalist David Wallace-Wells writes: "We have done more damage knowingly than we ever managed in ignorance."

What could explain this? "If you really understood the situation and still kept on failing to act, then you would be evil," says Thunberg. But our inertia is not straightforwardly a matter of malice, or even self-interest.

There seems to be an immense psychological obstacle in taking the future into account in the way that is now required of us. Just think of the contempt we show even to our future selves: we leave them to deal with our snowballing debts and missed deadlines and our smoking-related cancers. (The things I've done to my future self are criminal, and yet there will be no one around to be punished for these crimes. Only their victim.)

We have generated so many ways of defying our natural limitations. We can dart around the globe in mere hours; we can communicate with audiences of millions using just our thumb upon a screen; we can wage deadly warfare from the comfort of an office cubicle, and, as it turns out, we can change Earth's atmosphere.

But our moral psychology hasn't kept pace with these growing powers, or with the intricate links of cause and effect that turn our individually harmless actions into collective catastrophes.

It's an immense struggle for us to even imagine the new transgressions and categories of harm and injustice that we're now generating.

So we're inclined to say, in our defence, that it's much more complicated than Thunberg makes out.

It's complicated to address a collective action problem on such an unprecedented scale. It's complicated to know what's required of us personally and what can only be solved politically. It's complicated because we have invested so much in an idea of modernity that is premised on growth, and an idea of growth that is premised on burning through fuel.

It's complicated to get any one nation to forsake these ideas, and it's even more complicated to get all of them to forsake them simultaneously. It's complicated because, while some nations have been bingeing on this fuel for centuries now, others are only just arriving at the table.

It's complicated because there is now a conflict between remedying the injustices we've inherited from the past, and reducing the injustices we are perpetuating on the future.

All of this seems true enough. But complexity is also such a convenient alibi. It is here, especially, that Thunberg serves as a necessary corrective.

It is complex, yes, but it is simple too, in ways we mustn't lose sight of.

And if (to paraphrase activist and novelist Arundhati Roy) we must accept the adult obligation to never simplify what is complicated, we must also recognise the child's wisdom, and never complicate what is simple.

Have you seen the clip of the young boy realising, for the first time, that when we eat meat, we're eating animals? (If not, watch it below.) He looks about three years old.

"The octopus isn't real is it?" he asks.

I suppose he's double checking, because surely the octopus we marvel at in the aquarium and the picture books has nothing to do with the rubbery chunks on his plate? Surely we didn't behead an animal just to spruce up lunch?

It's extraordinary to watch: for the precocious and open-hearted child, yes, but also for his mother. She is present throughout his interrogation only as a kind and truthful answering voice.

"Why are you crying now?" he asks her eventually.

But we already know the answer. She's crying because his questions were once her questions, and the world's brutality was once not her fault. She's crying because she has just realised that now it is. 

GRETA THE INFLUENCER

One of the world’s most successful influencers, Thunberg is having a big impact in some unexpected circles:

FATBOY SLIM: Last weekend big beat music producer Fatboy Slim paid tribute to Greta by playing a mash-up of her UN speech and his late '90s club hit Right Here, Right Now at a show in England. The remix was originally created by SA electronica artist David Scott aka The Kiffness.

DONALD TRUMP: Tweeted a video of Greta delivering her speech, with a (must have been) sarcastic comment: 'She seems like a very happy young girl looking forward to a bright and wonderful future. So nice to see!'

BILLIE EILISH: Along with other singers Janelle Monée and Ellie Goulding and actors Mark Ruffalo and Leonardo DiCaprio, Eilish enthusiastically tweeted her praise of Greta.

TIME MAGAZINE: Has named Greta as one of the 100 most influential people of 2019.