A sandwich's carbon score highlights how even small daily choices connect to our wider environmental footprint. It's not unusual for people to share photos of their lunch. Now, they're sharing ready-made sandwiches labelled with carbon scores. These metrics show consumers how much of their "daily dietary carbon allowance" a humble sandwich consumes. As you can imagine, across social media, people expressed surprise not only at the scoring system but particularly at the idea of a "carbon allowance." But what is it really all about - saving the planet or selling virtue as a commodity?