Greenpeace has marked Google, Apple, and Facebook as the cleanest datacentre operators for transparency, policy, efficiency, and advocacy in its most recent Clicking Clean report, published this month.

Google received a B rating for transparency, B for policy, B for efficiency, and A for advocacy. Apple earned A, A, B, and A, while Facebook managed A, A, A, and B for the same categories. The three companies, alongside Box, Rackspace, and Salesforce, have committed to powering datacentres with 100 per cent renewable energy.

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Greenpeace's scorecard lists Apple as having already reached a 100 per cent clean energy index, while Google is split; 48 per cent sits within the clean energy index, 13 per cent in natural gas, and 22 and 15 per cent in coal and nuclear energy, respectively. Facebook is divided 49, seven, 25 and 16 per cent along the same categories.

Meanwhile, Greenpeace places Amazon Web Services (AWS) among the "dirtiest and least transparent companies in the sector." AWS has zero reporting of its energy or environmental footprint. Twitter falls under the same bracket.

Greenpeace said that since its last report, How Clean is Your Cloud?, published in April 2012, leading datacentre operators have moved towards improving energy efficiency, particularly from those which committed to build a 100 per cent renewably-powered platform.

At the same time, though, "despite the leadership and innovation demonstrated by green Internet pioneers, other companies lag far behind, with little sense of urgency, choosing to paper over their growing dirty energy footprints with status quo solutions."

According to Greenpeace, the growth of Cloud services would rank it as the sixth highest electricity consumer if compared beside countries. This is expected to increase by more than 60 per cent by 2020 as the (currently-estimated) 2.5 billion Internet population increases steadily.