Earth Hour, the voluntary one hour blackout observed by 187 countries on 23rd day of March every year, to mark a battle against global warming, was first organized by which organization of the following:

Option 1 -> Green Peace is an environmental organization focused on activism and campaigns, but did not organize Earth Hour.

Option 2 -> World Health Organization is a United Nations agency concerned with international public health, not environmental campaigns like Earth Hour.

Option 3 -> World Wildlife Fund for Nature (WWF) organized the first Earth Hour in Sydney, Australia in 2007 in partnership with the Sydney Morning Herald.

Option 4 -> People for Ethical Treatment of Animals (PETA) focuses on animal rights advocacy, not global climate initiatives.

Hence, Option 3: World Wildlife Fund for Nature -> WWF launched Earth Hour on March 31, 2007 in Sydney as a symbolic lights-out event to raise awareness about climate change, which later became a global movement observed annually on the last Saturday of March -> correct