This combination of pictures created on March 19, 2016, shows the Marina Bay Sands hotel and resort before (left) and during Earth Hour in Singapore. Millions of people from 178 countries and territories took part in WWF's Earth Hour this year. #

A before-and-after pair of images shows the Cologne Cathedral, a UNESCO World Heritage site, before and (click or tap to view) during Earth Hour in Cologne, Germany, on March 19, 2016. [Click or tap the image to view transition.] #

A pair of photographs show the financial district of Pudong before and (click or tap to view) during Earth Hour in Shanghai, China, on March 19, 2016. [Click or tap the image to view transition.] #

A general view of central Tokyo with the illuminated Tokyo Tower at the center is seen before and (click or tap to view) during Earth Hour, in Japan, on March 19, 2016. [Click or tap the image to view transition.] #

Photographs show the lights of the Sydney Opera House and Sydney Harbour Bridge before and (click or tap to view) after they were switched off for Earth Hour in Sydney, Australia, on March 19, 2016. [Click or tap the image to view transition.] #

The Petronas towers before and (click or tap to view) after the lights were switched off during the Earth Hour campaign in Kuala Lumpur on March 19, 2016. [Click or tap the image to view transition.] #

Before and (click or tap to view) after lighting is switched off to mark Earth Hour, in front of St. Basil Cathedral on Red Square in Moscow, Russia, on March 19, 2016. [Click or tap the image to view transition.] #

The Eiffel Tower in Paris before and (click or tap to view) after it went dark for the Earth Hour environmental campaign on March 19, 2016. [Click or tap the image to view transition.] #

The skyline of the Central Business District before and (click or tap to view) after lights were turned off during Earth Hour in Singapore on March 19, 2016. [Click or tap the image to view transition.] #

The Grand Palace before and (click or tap to view) during Earth Hour in Bangkok on March 19, 2016. [Click or tap the image to view transition.] #

The Kremlin towers and wall, the GUM department store, and the St. Basil's Cathedral before Earth Hour and (click or tap to view) after their lights were switched off in central Moscow, Russia, on March 19, 2016. [Click or tap the image to view transition.] #

Photos taken on March 19, 2016 show the Wat Arun (Temple of Dawn) lit and (click or tap to view) with lights turned off during Earth Hour in Bangkok. [Click or tap the image to view transition.] #

The Biyong Palace inside the Guozijian Imperial Academy is shown before and (click or tap to view) after having its lighting switched off to mark Earth Hour in Beijing on March 19, 2016. [Click or tap the image to view transition.] #

The Marina Bay Sands hotel and resort before and (click or tap to view) during the Earth Hour campaign in Singapore on March 19, 2016. [Click or tap the image to view transition.] #