In less than a decade, Copenhagen expects to become the first carbon-neutral city on the planet. There are plenty of reminders around the Danish capital to will the locals towards achieving a zero-carbon future by 2025: a 20-turbine wind farm, half of its population zipping around in bikes (and an infamous 180% import tax on cars), a mandatory green roof policy, or anti-food waste reminders on paper napkins. But among the most poetic interventions is…