For one hour, usually on the last Saturday in March, hundreds of millions of people across more than 190 countries deliberately switch off their lights at the same time. Earth Hour is WWF's global movement to spotlight climate and nature, and because the exact date shifts slightly each year (it occasionally moves a week earlier if it would otherwise collide with Holy Saturday), it's easy to lose track without a heads-up. Click the green Configure button and choose how far ahead you'd like to be alerted.
One city's idea that nobody expected to spread
The whole thing started small: a 2006 brainstorm at a Sydney hotel, under the working title "The Big Flick," between WWF Australia and an ad agency trying to find a way to talk about climate change without resorting to fear tactics. On March 31, 2007, more than 2.2 million people and 2,000 businesses in Sydney switched off their lights for an hour, cutting the city's electricity use by over 10% — the equivalent of taking roughly 48,000 cars off the road for that hour. Nobody involved expected it to become a recurring global event; it just kept growing every year after that.
From one city to a worldwide ritual
By its second year, Earth Hour had reached 35 countries and an estimated 50 million people. Within a few more years it was being marked by over 7,000 cities across more than 150 countries, with globally recognizable landmarks — the Eiffel Tower, the Sphinx, the Forbidden City, Christ the Redeemer — going dark in solidarity. Even Antarctica's Scott research base joins in by switching off non-essential equipment.
More than just an hour
The lights-out moment is really just the visible tip of Earth Hour — WWF uses the attention it generates to run accompanying petitions and advocacy pushes each year. One of those, a WWF-Russia petition run as part of an Earth Hour campaign, collected over 122,000 signatures and led to a new law protecting Russian seas from oil pollution. Similar Earth Hour campaigns have helped secure a marine protected area in Argentina and a plastic bag ban in the Galápagos — concrete policy wins that came directly out of that year's Earth Hour push, not just the hour of darkness itself.
Not everyone's numbers cooperate
Not every city sees a tidy drop in electricity use. Calgary, Canada is the famous outlier — its power consumption has actually increased during Earth Hour in multiple years, an effect researchers mostly attribute to cold weather driving up heating demand regardless of the lights being off.
So whether you're planning to switch off at home or just want to catch which landmarks go dark this year, click that green Configure button and let the date come to you.