In Okinawa and beyond, green curtains of bitter melon slash indoor heat and AC use with style and simplicity.
What unsustainable behaviour needs to change:
In urban summer heat, air conditioning often becomes a default behaviour—especially in poorly insulated buildings. But cooling our homes with energy-intensive appliances drives up electricity use, strains power grids during peak hours, and contributes to carbon emissions. Japan’s data shows that AC demand can rise by over 20% during summer heatwaves.
This dependency is reinforced by habits, perceived lack of alternatives, and the “invisibility” of passive cooling options. Our brains are wired to favour quick, effort-minimising fixes—even when greener solutions exist.
The Green Nudge:
Japan’s “Green Curtain” programme offers a refreshing alternative—literally. Local governments distribute free starter kits — seeds (like bitter melon, morning glory or cucumber), netting and instructions — to schools, homes and public offices. As the vines climb façades and windows, they shade walls, block direct sunlight, and cool the air through natural evaporation. Many households even enjoy fresh vegetables from their vines.
The nudge works on three key behavioural principles:
Ease: Free starter kits lower the barrier to action.
Salience: Green façades serve as visible cues that spark imitation.
Social proof: Public curtain maps and neighbourhood contests promote friendly competition and norm-setting.
The results: Empirical trials show indoor temperatures drop by 2–3 °C in shaded rooms. During peak hours, this translates into an average 20% reduction in AC electricity use, helping lower energy bills, reduce emissions, and ease grid pressure. It’s a simple, nature-based intervention with measurable impact—scaled across more than 80 Japanese cities.
Do you know of any other nudges that help cool cities or fight urban heat? Feel free to comment or get in touch: hello@green-nudges.com
From the Green Nudges Consulting team, drawing on insights from Japan’s “Green Curtain” initiative — launched in Okinawa in 2007 and now spreading to over 80 cities.
