How do you price the death of the world?

Climate change is hard to account for.

Grist's David Roberts writes about the distinction between climate change and other environmental problems:

The first difference is that carbon dioxide is not like other pollutants… The typical climate-policy targets that get thrown around — reducing emission rates by 80 percent by 2050, for example — are relatively meaningless. They focus on the rate of flow from the faucet. But that’s not what matters. What matters is the amount in the tub. If the tub fills up enough, global average temperature will rise more than 2 degrees Celsius and we’ll be in trouble. Avoiding that — staying within our “carbon budget” — is the name of the game.

The second difference is that climate change is irreversible.

Roberts cites a 2009 paper from Nature, "among many others":

The climate change that takes place due to increases in carbon dioxide concentration is largely irreversible for 1,000 years after emissions stop. Following cessation of emissions, removal of atmospheric carbon dioxide decreases radiative forcing, but is largely compensated by slower loss of heat to the ocean, so that atmospheric temperatures do not drop significantly for at least 1,000 years.

Climate change is notoriously tricky to deal with in standard economic terms. Part of it is that, to any normal person, something which is irreversible for 1,000 years sounds at least ten times worse than something which is irreversible for 100 years, if not even worse still.

Economically, though, the two are essentially the same. "Present value" is an economic concept dealing with the fact that money in the future is worth less than money now – because you can always invest money now and have more money in the future. Of course, that assumes long-term growth, which, if we're talking about world-changing events like anthropogenic climate change, might not be a safe assumption.

But the end result of the calculations is that nearly any cost beyond a hundred years into the future isn't worth spending money today to avoid. The intuitive conclusion – that it's worth fighting climate change harder if it will last for a millennium than a century – isn't the case. Assuming growth.

But there are even bigger problems for climate change than that. The vast majority of economic responses to it require calculating a "likely cost", and then applying that to the measures proposed to combat it. So, for example, a properly implemented carbon tax requires a calculation of the damage one tonne of CO2 does to the environment, in order to accurately price in the negative externalities.

Unfortunately, conventional ways of pricing risk rather fall over when considering something like climate change, because it carries a non-zero risk of existential threat. That is, there are proposed mechanisms whereby "runaway climate change" could present a civilisation-ending threat.

How do you price the end of civilisation? One option is to look at the value of everything in the world. It would be quite an accounting task, and one faced by the UK government last year when they had to put a price on Stonehenge to fulfil new bookkeeping requirements. The American government puts the value of the entirety of the US at $110trn, so it seems likely that the value of all the world's civilisations is well into 16 figures.

That's high, but it's countable. The real issue comes when you look at an alternative way of measuring the cost of risk, which is the amount you would pay to prevent it. Presumably, there is no sum which would not be worth spending to prevent the end of civilisation. Any cost would be less than the destruction of everything.

By that measure, then, the damage caused by an existential threat is infinite. But the problem with infinite quantities is that they don't work very well in conventional mathematics. Back to the normal risk accounting: you typically multiply the damage you are risking with the chance it will happen. So we are happy to suffer high risk of low damage – like groping for a glass of water at midnight with the lights off – or low risk of high damage – like driving a car – but not high risk of high damage – like driving a car at midnight with the lights off.

But infinity multiplied by anything other than zero is still infinity. Conventional risk assessment simply falls apart when confronted with something the magnitude of the worst possibilities of climate change.

Note too that it doesn't require the risk to be large. I think the risks of climate change are greater than most, but I also think it's extraordinarily unlikely that it actually would result in the end of civilisation. But can we rule it out with certainty?

The best way to look at it is to compare it to our every day lives. Thousands of people are killed crossing the road every day. To do so carries a non-negligible personal existential threat – that is, you might die. Yet I see people dodging traffic to get to work 30 seconds earlier every day, which suggests that, instinctively, we don't treat the risk of death with as much weight as we perhaps should.

But I think theres a different motivator at work. We know death is bad, and that it's worth doing a lot to try and avoid it; but we also know death can come from any corner. And the same is true of fighting existential threats to civilisation. If we could spend ludicrous sums to eliminate them all, it might be worth it; but who's to say we won't prevent climate change, only to die from an asteroid hit? Or cap our future development by not experimenting with nanotech, only for an angry AI to kill us in our sleep?

Climate change could be very, very bad indeed. But making the important choices about the trade-offs we should make to fight it are hard because, not despite, its seriousness.

Photograph: Getty Images.

Alex Hern is a technology reporter for the Guardian. He was formerly staff writer at the New Statesman. You should follow Alex on Twitter.

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Piers Morgan struggles with the idea that anyone might ever refuse an opportunity to go on television

The Good Morning Britain host has contradictory beef with Ewan McGregor.

Has it been a while since you heard what Piers Morgan thinks? Are you shaking from withdrawal, refreshing your Twitter feed, unsure whether Kanye is or isn’t a narcissist? Well, fear not, the Mole has a fresh fix for you. After Ewan McGregor dropped out of appearing on Good Morning Britain today, a new take was born. Actors’ opinions are stupid, but also, actors should come on Piers Morgan's show and talk about their not-important views.

McGregor, who was meant to be promoting Trainspotting T2 on the show, tweeted this morning he had cancelled because of Piers’ (obviously half-baked) opinions on the Women’s March. “Was going on Good Morning Britain, didn't realise @piersmorgan was host,” McGregor wrote. “Won't go on with him after his comments about #WomensMarch.”

What truthbomb had Piers dropped to provoke this? That it was unfair women were protesting and where was the MEN'S march. A march for men! As if running our parliament, corporate system, legal industry and creative sector isn’t enough! They should probably all do a walk too! Poor men. No wonder the patriarchy is on its last legs. They must be so weary.

Still, hats off to Piers Morgan. It takes a real personal flexibility to maintain the title of Contrarian Extraordinaire of the Our Glorious Nation. By which we mean that Piers Morgan will think literally anything, if the money is right. Whether it’s writing that Kim Kardashian is so awful she caused someone to have a stroke, or that he loves her for being herself, the man is so darn unpredictable. 

Morgan accused McGregor of being "just an actor", and that he should be “big enough to allow people different political opinions”. Once again, he asked the age-old question: are you an enemy of free speech if you won't go on someone’s early morning television show? This might be alien to Piers, but people don't have to go on television if they don't want to. 

And what if Ewan had appeared on the show chatting about his film? “Happy to appear on my show for your film, but not happy with my opinions? Classic money-driven actor,” the inevitable Morgan tweet would have read. It's quite easy, this Piers Morgan lark. No, it isn't. Yes it is. Cheque please! 

I'm a mole, innit.