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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PMQs review: Jeremy Corbyn prompts Tory outrage as he blames Grenfell Tower fire on austerity

To Conservative cries of "shame on you!", the Labour leader warned that "we all pay a price in public safety" for spending cuts.

A fortnight after the Grenfell Tower fire erupted, the tragedy continues to cast a shadow over British politics. Rather than probing Theresa May on the DUP deal, Jeremy Corbyn asked a series of forensic questions on the incident, in which at least 79 people are confirmed to have died.

In the first PMQs of the new parliament, May revealed that the number of buildings that had failed fire safety tests had risen to 120 (a 100 per cent failure rate) and that the cladding used on Grenfell Tower was "non-compliant" with building regulations (Corbyn had asked whether it was "legal").

After several factual questions, the Labour leader rose to his political argument. To cries of "shame on you!" from Tory MPs, he warned that local authority cuts of 40 per cent meant "we all pay a price in public safety". Corbyn added: “What the tragedy of Grenfell Tower has exposed is the disastrous effects of austerity. The disregard for working-class communities, the terrible consequences of deregulation and cutting corners." Corbyn noted that 11,000 firefighters had been cut and that the public sector pay cap (which Labour has tabled a Queen's Speech amendment against) was hindering recruitment. "This disaster must be a wake-up call," he concluded.

But May, who fared better than many expected, had a ready retort. "The cladding of tower blocks did not start under this government, it did not start under the previous coalition governments, the cladding of tower blocks began under the Blair government," she said. “In 2005 it was a Labour government that introduced the regulatory reform fire safety order which changed the requirements to inspect a building on fire safety from the local fire authority to a 'responsible person'." In this regard, however, Corbyn's lack of frontbench experience is a virtue – no action by the last Labour government can be pinned on him. 

Whether or not the Conservatives accept the link between Grenfell and austerity, their reluctance to defend continued cuts shows an awareness of how politically vulnerable they have become (No10 has announced that the public sector pay cap is under review).

Though Tory MP Philip Davies accused May of having an "aversion" to policies "that might be popular with the public" (he demanded the abolition of the 0.7 per cent foreign aid target), there was little dissent from the backbenches – reflecting the new consensus that the Prime Minister is safe (in the absence of an attractive alternative).

And May, whose jokes sometimes fall painfully flat, was able to accuse Corbyn of saying "one thing to the many and another thing to the few" in reference to his alleged Trident comments to Glastonbury festival founder Michael Eavis. But the Labour leader, no longer looking fearfully over his shoulder, displayed his increased authority today. Though the Conservatives may jeer him, the lingering fear in Tory minds is that they and the country are on divergent paths. 

George Eaton is political editor of the New Statesman.

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