The debate is not short of arguments, it is short of units

Paul Luttikhuis wrote about climate for the Dutch daily NRC for twenty-five years, and he signed off with a long valedictory essay. It is worth reading for one reason above all others: it is honest about its own shortcomings. He describes standing in the press room in Paris in December 2015 with a lump in his throat, deciding not to join the applause. He describes hearing a glaciologist tell a room of bankers that the next fifteen years would settle the climate of the next ten thousand, then making small talk at the drinks afterwards and joining the traffic queue home. And he closes, after a quarter of a century, by saying he still does not know the answer.

That is not a failure of the writer. It is a symptom, and you can locate it precisely, at the points where he needs a quantity.

Five times in the essay a measure is called for, and five times an image arrives instead. Wealthy countries are elephants and poor countries are mice. Economic climate models are a game of Monopoly. Every person is entitled to the yield of two hectares of land. We are the colonisers of future generations. We must stop dreaming of escape and find a territory to land on. Each is well made. Each is a metaphor. You cannot calculate with any of them, compare across them, or be shown wrong by them.

Metaphor is what you reach for when the unit is missing.

The missing units are not exotic. They sit in the literature the author drew on for twenty-five years. The distinction between magnitude and rate, which is why a carbon release larger than ours was less disruptive than ours, because it took millennia where ours takes centuries. The distinction between a projection and an observation, which decides whether a technology is an achievement or a promise. The discount rate, the annual percentage by which we write the future down, which presents itself as a technical parameter while encoding a moral judgement about how much people who do not yet exist are worth. Threshold behaviour with hysteresis, where the way back is not the way out. The migration speed of ecosystems, in hundreds of metres per year, set against the speed at which isotherms move across the land surface, in kilometres per year. And the difference between the clock an electoral cycle runs on and the clock of the system that cycle is meant to govern.

English, unlike Dutch, has serviceable words for all of these. That turns out not to help much. The terms exist, they are stable, and they have simply never made the crossing from the journals into the register in which the public argument is conducted. Discount rate is plain enough English and remains, in practice, a word that tells a general reader the paragraph is not addressed to them. And where a term has made the crossing, the crossing itself has costs. Tipping point got out, took hold, and is now applied to more or less any development that feels dramatic, usually with no threshold or hysteresis anywhere near it. A word in circulation is necessary and not sufficient. It still has to hold its meaning once it is loose.

Climate journalism has coined terms of its own, and it is telling which ones. The trade talks about agency, about giving readers something to do, about solutions journalism. Luttikhuis is visibly irritated by the demand, rejects it, and then supplies the list anyway: buy less, stop flying, get rid of the car, live in a smaller house. He adds that nobody wants this, himself included. That is an answer to a problem of international coordination given in the units of a household. The vocabulary of agency does not expose that shift of level, it covers it over. Which is why the demand keeps failing to satisfy anyone, and why the usual explanation, that people are unwilling, is the wrong diagnosis.

The same poverty explains the axis the whole debate runs along, with the believer at one end and the denier at the other. That axis is not primarily a product of polarisation. It is a product of a thin vocabulary. Positions you cannot express in different units collapse into each other. An engineer who thinks a given electrification schedule is unachievable and a man who denies the greenhouse effect end up at the same coordinate because there are no words available that would tell them apart. Pull the questions apart, and most of the disagreement turns out not to be about the science at all.

Deep time is where these units come from, because the geological archive is the only laboratory in which the experiment has already been run many times over. And the archive answers consistently in a different quantity from the one the question was asked in. The public debate asks how much. The archive answers how fast.

A journalist who felt the right discomfort for twenty-five years, wrote it down honestly, and had to record at the end that he does not know the answer is not an opponent of this argument. He is the case for it.