Facebook is getting some green love from Greenpeace.

The activist environmental organization declared victory in its nearly two-year campaign to pressure Facebook to reduce the environmental impact of its data centers. The social media giant’s data centers house a colossal arsenal of servers that supports the friendships and marketing campaigns of 800 million people across the globe.

Most of the electricity that powers Facebook’s data centers — and most other data centers — comes from coal-fired power plants. Greenpeace’s Facebook campaign, dubbed Unfriend Coal and centered on a Facebook page,...