Your cat may count against the household

Under a household carbon budget of the kind periodically proposed by policy researchers, a pet cat would be entered on the same ledger as the boiler, the car and the second flight. The classified pages would adjust first.

Personal or household carbon allowances have been proposed and studied repeatedly since the 2000s as a way of rationing emissions at the level of the individual rather than the industry, and the idea resurfaces whenever national carbon budgets tighten. Separately, researchers have examined the environmental footprint of pet ownership, particularly the meat-heavy diets of cats and dogs, and pet-food makers have started marketing insect-based and plant-based products partly on climate grounds. Carbon labelling of food products and rehoming listings for pets citing cost-of-living pressures are both already familiar. Compulsory microchipping and registration of pet cats has been introduced in some countries, creating the administrative record such a scheme would need.

FOR REHOMING. Neutered male tabby, six years, indoor, good with children, vaccinated, microchipped. Comes with 2030 allowance already loaded (0.31 tonnes remaining, wet food only). Serious homes only. Would suit a single-person household or a couple who have given up flying. Reason for sale: new baby. No time-wasters. Litter tray, carrier and carbon certificate included. Collection from the north side of town, weekday evenings. £40 or nearest offer, or free to a household with headroom.

The advertisement, of a kind that would appear on regional listings sites within weeks of the scheme starting, would be typical of the market a household carbon budget would create. Under the scheme, each address would receive an annual emissions allowance, drawn down by heating, driving, food and anything else that could be metered. A cat, fed largely on meat and kept at room temperature for its entire life, would be assessed as a dependent with no income. The registry would express this as a fixed annual deduction per animal, adjusted for body weight and diet class. The cat would not be consulted.

Janet Coyle, who placed the advertisement, said the decision had been made on a spreadsheet at the kitchen table. “We ran the numbers and it was the cat or the tumble dryer,” she said. Her partner had argued for the cat. The dryer, the registry pointed out in an automated letter, could be replaced with a more efficient model, while the cat could not be upgraded. They had tried an insect-protein diet, which would move him to a lower band, but he refused it for eleven days. “He looked at us like we had betrayed him,” she said. “Which we had.”

Rehoming listings would develop their own vocabulary within a season. A cat described as “light” would be small, elderly, or on dry food. “Headroom” would mean a household with unused allowance, typically pensioners who no longer drove or families that had already given up a car. Kittens, with a full lifetime of deductions ahead of them, would be advertised with the phrase “long-term commitment” in a tone previously reserved for mortgages. Shelters would begin listing the annual carbon cost beside the adoption fee, in a smaller font.

A spokesperson for the regional carbon registry said the scheme did not require anyone to give up a pet. “Households remain entirely free to keep animals within their allowance,” she said, adding that the deduction for a cat was, in most cases, smaller than that of a single return flight to the Mediterranean. This comparison would become the most quoted sentence in the scheme's guidance, largely by parents explaining to their children why it was the holiday that had been cancelled instead.

On the other side of the market, Rob Hesketh, a retired postal worker with a bus pass and an unused allowance, said he had taken in three cats since spring. “People keep offering to pay me,” he said. He had declined the money but accepted the litter trays. His daughter had suggested he was being exploited. He said he had spent forty years delivering other people's letters and this was the first time anyone had delivered anything to him. The third cat, he added, had arrived with its own certificate laminated.

Veterinary practices would be required to update the registry on any change of diet, weight class or death, the last of which would release the allowance back to the household within one billing cycle. Pet insurers would begin offering a product that paid out not for the animal but for the emissions, covering the shortfall if a cat lived longer than its actuarial estimate. One of the larger pet-food manufacturers would print the deduction band on the tin beside the feeding guide. The cats, according to every owner interviewed, would continue to sleep on the warmest available surface, which would also be metered.

Mrs Coyle's advertisement would be answered within a day by a woman in a flat two streets away who had recently stopped flying to see her sister. The handover would take place on a Tuesday evening, in the car park of a discount supermarket, with the certificate passed across in a plastic wallet. The cat would sit in the carrier and look at neither of them. Mrs Coyle would drive home, put the dryer on, and, by her own account, sit down on the kitchen floor for a while.