Prime Minister Justin Trudeau joined Canadian organizers of Earth Hour in asking Canadians to turn their lights off Saturday night along with millions around the world.

Celebrate <a href="https://twitter.com/earthhour">@EarthHour</a>! Shut off your lights tonight at 8:30 – then work and live to <a href="https://twitter.com/hashtag/ChangeClimateChange?src=hash">#ChangeClimateChange</a> every single day. —@JustinTrudeau

"We're all on this planet together," Trudeau later tweeted, hinting the upcoming federal budget would contain measures to deal with climate change.

"Tweeting about Earth Hour is one thing. Tuesday, we'll put words into action with a budget that builds a clean economy for Canada."

A spokeswoman for Trudeau said the lights were turned off at the Rideau Hall cottage in Ottawa where the Prime Minister and his family are temporarily living while the official residence at 24 Sussex Drive is being renovated.

Some of Trudeau's cabinet ministers also took to social media with Environment Minister Catherine McKenna making a series of tweets and International Trade Minister Chrystia Freeland also noting the occasion.

The event was launched in Australia in 2007 as a way to draw attention to environmental issues including climate change, but this year's 10th edition is as much a celebration as a call for action, according to the main organizer of the event.

A crowd marked Earth Hour with candles on Parliament Hill in 2010 when the lights went out. (Ashley Fraser/Canadian Press)

"This year, because the nations came together in Paris in December for the first time and agreed on a plan of action, I think the goal is not only to draw attention but also to celebrate the fact we've seen really important action on this critical challenge," said David Miller, CEO of World Wildlife Fund Canada.

In addition to the Paris climate conference, Miller pointed to recent premiers' meetings as well as agreements between Trudeau and U.S. President Barack Obama as a sign of "tremendous momentum" on climate change in Canada.

While asking Canadians to switch off their lights from 8:30 p.m. to 9:30 p.m. local time, organizers wanted them to turn their smartphones on.

The World Wildlife Fund was encouraging social media users to "donate" their Facebook feeds to display messages about climate awareness, or to add an Earth Hour filter to their Facebook and Twitter profile pictures.

It was not immediately clear how many Canadians took part in this year's Earth Hour.

Toronto Hydro tweeted Saturday night that the city's electricity use dipped by 3.2 per cent, which the utility said was the equivalent of taking 36,000 homes off the grid.

PowerStream, which serves nine municipalities north of Toronto, reported a 4.3 per cent drop in electricity consumption during Earth Hour. That was down slightly from the six per cent reduction achieved last year.

While Earth Hour grew to include 7,000 cities in 172 countries last year, some say the event has been losing steam in recent years, at least in Canada.

BC Hydro, for example, said British Columbians reduced the provincial electricity load during Earth Hour by just 0.2 per cent last year — much less than the two per cent reduction recorded in 2008.

Science World, seen here before and during Earth Hour, was one of many Vancouver landmarks that went dark in 2009. But overall electricity savings during the event appear to be declining year over year in some Canadian cities. ((CBC))

Miller said critics who measure the event's success in megawatt hours are missing the point.

"Earth Hour has been part of a movement that has made a very real difference and I think this year we have to celebrate that success," he said. "It's certainly never been about the amount of energy saved on the night."