The wind power will come from a 204MW project about 90 miles distant under development by 50-50 owners British Columbia-based Alterra Power and US infrastructure investor Starwood Energy Group.

They will sell most of the electricity under a 13-year financial hedge contract to Houston-based Citigroup Energy, a power distributor, who will supply some to Facebook.

"Thanks to our continued focus on efficiency and our investments in renewables in recent years, the carbon impact of one person’s use of Facebook for an entire year is the same as the carbon impact of a medium latte," says Jay Parikh, Facebook's vice president of infrastructure engineering.

"We