Landmarks from the Sydney Opera House to the Golden Gate Bridge in San Francisco plan to turn off their lights for the event, pioneered by Australia last year.

Organisers of “Earth Hour” say the idea is to make people aware of the links between global warming and electricity, which is usually generated by burning fossil fuels such as coal and oil which emit greenhouse gases. They say 24 large cities around the world are taking part. Last year 2.2 million Sydney residents switched off the lights.

I suppose that if you were in space and it went to plan, you might see successive bands of the earth dim slightly on the stoke of 8 p.m. — a bit like a slow Mexican wave in a soccer stadium.

Then again the dimming will probably be hard to spot: street lamps and other lights needed to discourage a one-hour bonanza for burglars or muggers will stay on.

Is this is a great idea or just a gimmick?

Have past initiatives to raise public awareness of the way individuals can help fight climate change, such as the Live Earth concerts organised by former U.S. Vice-President Al Gore in July last year, had a lasting effect?

Will you be turning off your lights?