[A] At their worst, such rulings is based on a wrong logic. Greenhouse gases that have been released by the construction of an existing building will heat the planet whether the building is abandoned, renovated or knocked down. The emissions have been taken out of the world’s “carbon budget” , so treating them as a new building means double counting. Even when avoiding this error, embodied emissions must be treated carefully. The right question to ask is a simpler one: is it worth using the remaining carbon budget to renovate a building or is it better to knock it down?

[B] Targeted subsidies, especially for research and development into construction materials, as well as minimum-efficiency standards, could bolster the impact of carbon pricing, speeding up the pace at which the built environment decarbonises. What will never work, however, is allowing the loudest voices to decide how to use land and ignoring the carbon emissions of their would-be neighbours once they are out of sight.

[C] Choosing between these possibilities requires thinking about the unseen. It used to be said that construction emitted two types of emissions. As well as the embodied sort in concrete, glass and metal, there were operational ones from cooling, heating and providing electricity to residents. The extra embodied-carbon cost of renovating a building to make it more energy-efficient can be justified on the grounds of savings from lower operational-carbon costs.

[D] Conserving what already exists, rather than adding to the building stock, will avoid increasing embodied emissions—or so NTMBYS, not-in-my-backyard residents who oppose local construction, often suggest. The argument is proving to be an effective one. On March 12th the EU passed a directive requiring buildings constructed after 2030 to produce zero emissions over their lifetime. Last month the British government attempted to reject proposals from Marks & Spencer, a department store, that would involve rebuilding its flagship shop in London, on the grounds knocking it down would release 40,000 tonnes of embodied carbon.

[E] These two types of emissions might be enough for the architects designing an individual building. But when it comes to broader questions, economists ought also to consider how the placement of buildings affects the manner in which people work, shop and, especially, travel. The built environment shapes an economy, and therefore its emissions. In the same way as the emissions from foot-dragging over the green transition are in part the responsibility of climate-change deniers, so NIMBYS are in part responsible for the emissions of residents who are forced to live farther from their work in suburbs.

[F] Deciding such choices on a case-by-case basis makes little sense. The more sensible approach is to use a carbon price, rather than a central planner’s judgment. Putting a price on the remaining carbon budget that can be used for new physical infrastructure, as well as the services that people use in their homes, means that the true climate cost of each approach has to be taken into account. Under such a regime, energy-efficient homes close to public transport would be worth more. Those with less embodied carbon would be cheaper to build. Developers that knocked buildings down and densified would therefore often be rewarded with larger profits.

[G] To most NIMBYS, the residents who are prevented from living in new housing are an afterthought. Yet wherever else they live, they still have a carbon footprint, which would be lower if they could move to a city. Density lowers the per-person cost of public transport, and this reduces car use. It also means that more land elsewhere can be given over to nature. Without knocking buildings down and increasing density, potential residents would typically have to move to the suburbs instead, saving money on rent but consuming more energy, even if the government succeeds in getting more drivers into electric vehicles.

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