It's aim is to draw attention to the large impact a small action can have if millions of people participate.
More than 680 employees of the City are being encouraged to take part between 830 and 930 tomorrow night. Sustainable Saint John and its 35 member businesses are also taking part.
Earthhour.org says more than 70 per cent of the world's CO2 emissions is generated by cities.
A "Lights Out" walk around Lily and Fisher Lakes in Rockwood Park is coming up tomorrow.
Participants are asked to meet at the Interpretation Centre at 815pm.
The first Earth Hour was held in Sydney, Australia back in 2007 involving 2.2 million and 2100 businesses. It has grown to include 7000 cites and towns in a 152 countries across the globe switching off their lights for Earth Hour.
