A credit card that limits users’ carbon footprints is the winner of the Creative eCommerce Grand Prix at Cannes.

Do Black, developed by Swedish fintech company Doconomy and agency RBK Communication in Stockholm, aims to help consumers overspending on the levels of carbon dioxide caused by their consumption. The card tracks users' carbon footprint purchase by purchase using an app, and if they outspend the limit (calculated according to the amount it will take for each person to cut their carbon emissions by 50 percent by 2030), it will block their next transaction.

While the Do Black card is still a pilot project, the jury president, Global Chief Creative Officer at Wunderman Daniel Bonner, stressed that it was "real" and the cards would be going out to consumers soon.

Bonner said the Grand Prix went to Do Black because it's a "well-researched, beautifully simple idea and the execution was stunning."

He added: "It's very difficult to make that kind of payment solution something that consumers are emotionally connected to. It stood out and we couldn't ignore it right from the beginning. It ticked every box—ideas people would learn from, ideas they'd want to steal, the wow factor. It's also sustainable and scalable."

It's the second year of the Creative eCommerce Lions, and Bonner says the category was still finding its feet. A key trend noticed on the jury was "atomization of retail", he said. "People don't just buy from stores now or online but from anywhere—live TV, posters, graffiti, their friends as resellers."

However, the Grand Prix didn't fit that trend and that made it unique, he added. 

Do Black beat competition including Burger King's "Whopper Detour," which won the Direct Grand Prix yesterday, and KFC China's Christmas Pocket Store, which won a Gold Lion.