Carbon removal may come with an expiry date

Consider a sustainability report of the kind that will be published in enormous numbers over the next few years. On page sixty-one, under a heading nobody reads, a line would appear stating that a portion of the carbon dioxide removal certificates retired against the company's 2030 neutrality position have reached the end of their monitored durability period, and that the position has therefore been restated.

The word doing the work is restated. The company would not be accused of anything. It bought removals, it retired them, it published the figure, and the figure was correct at the time. What would have changed is not the company's conduct but the carbon's: it left the ground earlier than the paperwork assumed.

The mechanism would be familiar to anyone who has ever held a bond. Removals come with durations. Wood and soil hold carbon for decades, biochar for longer, and mineralisation or geological storage for spans measured in the kind of numbers that make a treasury department uneasy. A tonne is a tonne only as long as nobody asks for how long — and the entire apparatus of corporate climate accounting was built by people who did not ask.

“Nothing has been reversed,” a finance director would say, on a call where that sentence would be technically true. “A durability window has closed. We are restating a prior-period environmental position. I would note for the record that this is the first time this company has reopened a closed year because of a forest.”

The remedy would be the one the market has already invented: a buffer account, a shared pool of unsold removals held back precisely so that somebody's fire, flood or beetle can be paid for out of a common reserve. It works. It is also, structurally, insurance — which means the question of how much buffer is enough would become an actuarial question about forests, asked by people trained in spreadsheets.

The awkward part would begin downstream. A product sold as neutral, a flight sold as neutral, a year of operations signed off as neutral: each rests on the certificate underneath it, and a certificate that expires makes every claim above it provisional. The genuinely new object in this scenario would be the climate equivalent of a recall notice, issued not because the product failed but because the compensation did.

None of this requires a new technology. It requires only that durability be written on the certificate, that monitoring continue after the sale, and that somebody be liable when the number moves. All three are currently being written into rules. The expiry date is not the joke. The expiry date is the design.