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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The Women's March against Trump matters – but only if we keep fighting

We won’t win the battle for progressive ideas if we don’t battle in the first place.

Arron Banks, UKIP-funder, Brexit cheerleader and Gibraltar-based insurance salesman, took time out from Trump's inauguration to tweet me about my role in tomorrow's Women’s March Conservative values are in the ascendancy worldwide. Thankfully your values are finished. . . good”.

Just what about the idea of women and men marching for human rights causes such ill will? The sense it is somehow cheeky to say we will champion equality whoever is in office in America or around the world. After all, if progressives like me have lost the battle of ideas, what difference does it make whether we are marching, holding meetings or just moaning on the internet?

The only anti-democratic perspective is to argue that when someone has lost the argument they have to stop making one. When political parties lose elections they reflect, they listen, they learn but if they stand for something, they don’t disband. The same is true, now, for the broader context. We should not dismiss the necessity to learn, to listen, to reflect on the rise of Trump – or indeed reflect on the rise of the right in the UK  but reject the idea that we have to take a vow of silence if we want to win power again.

To march is not to ignore the challenges progressives face. It is to start to ask what are we prepared to do about it.

Historically, conservatives have had no such qualms about regrouping and remaining steadfast in the confidence they have something worth saying. In contrast, the left has always been good at absolving itself of the need to renew.

We spend our time seeking the perfect candidates, the perfect policy, the perfect campaign, as a precondition for action. It justifies doing nothing except sitting on the sidelines bemoaning the state of society.

We also seem to think that changing the world should be easier than reality suggests. The backlash we are now seeing against progressive policies was inevitable once we appeared to take these gains for granted and became arrogant and exclusive about the inevitability of our worldview. Our values demand the rebalancing of power, whether economic, social or cultural, and that means challenging those who currently have it. We may believe that a more equal world is one in which more will thrive, but that doesn’t mean those with entrenched privilege will give up their favoured status without a fight or that the public should express perpetual gratitude for our efforts via the ballot box either.  

Amongst the conferences, tweets and general rumblings there seem three schools of thought about what to do next. The first is Marxist  as in Groucho revisionism: to rise again we must water down our principles to accommodate where we believe the centre ground of politics to now be. Tone down our ideals in the hope that by such acquiescence we can eventually win back public support for our brand – if not our purpose. The very essence of a hollow victory.

The second is to stick to our guns and stick our heads in the sand, believing that eventually, when World War Three breaks out, the public will come grovelling back to us. To luxuriate in an unwillingness to see we are losing not just elected offices but the fight for our shared future.

But what if there really was a third way? It's not going to be easy, and it requires more than a hashtag or funny t-shirt. It’s about picking ourselves up, dusting ourselves down and starting to renew our call to arms in a way that makes sense for the modern world.

For the avoidance of doubt, if we march tomorrow and then go home satisfied we have made our point then we may as well not have marched at all. But if we march and continue to organise out of the networks we make, well, then that’s worth a Saturday in the cold. After all, we won’t win the battle of ideas, if we don’t battle.

We do have to change the way we work. We do have to have the courage not to live in our echo chambers alone. To go with respect and humility to debate and discuss the future of our communities and of our country.

And we have to come together to show there is a willingness not to ask a few brave souls to do that on their own. Not just at election times, but every day and in every corner of Britain, no matter how difficult it may feel.

Saturday is one part of that process of finding others willing not just to walk a mile with a placard, but to put in the hard yards to win the argument again for progressive values and vision. Maybe no one will show up. Maybe not many will keep going. But whilst there are folk with faith in each other, and in that alternative future, they’ll find a friend in me ready to work with them and will them on  and then Mr Banks really should be worried.