Clean technology: Facebook comes clean on carbon

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The juggernaut social media website has revealed the carbon footprint of its operations, possibly to show up its rival Google.

The CO2 emissions from keeping Facebook's 900m users up and running equate to 285,000 metric tons of CO2 in 2011, compared with Google's 1.5m tons. 72% of Facebook's emissions come from the huge data centres and energy used to run them.

Half of the power used is generated by burning coal and gas, which accounts for the high carbon footprint.

Averaged out per user, the emissions equal 269 grams, or around the equivalent of a cup of coffee, said the company.

Last year Facebook announced it would build a green data centre in Sweden, taking advantage of the country's cold climate to keep servers cool.