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When the first comprehensive report in years to examine energy use by computer servers was published in February 2007, it was greeted with surprise by industry insiders. Jonathan Koomey, a staff scientist at Lawrence Berkeley National Laboratory in California, found that worldwide power consumption by servers had doubled between 2000 and 2005. “Everyone thought CO₂ emissions were a problem for transportation and big energy,” says Bill St Arnaud of Canarie, Canada’s internet development organisation in Ottawa, Ontario.

Since then a raft of have highlighted the rocketing energy demands made by computers (See Chart). One of them, a…