Q: What's the difference between an SUV, a server and ten 65 watt light bulbs? A: Apparently nothing when it comes to carbon emissions

In my May 16th post, Server Footprint from SUV to Light Bulb Equivalent in 5 months, I mentioned further exploring the carbon footprint comparison among servers, standard light bulbs and SUVs. Now, here’s my take.

The December 2007 report, An Inefficient Truth, states that “a medium sized server has roughly the same annual carbon footprint as an SUV doing 15 miles per gallon.”
In an apparent amazing leap of improvement in only five months, an EU paper from May 2008, Addressing the Challenge of Energy Efficiency through Information and Communication Technologies, states "the most advanced computer servers consume the same amount of energy as a standard light bulb”.

From an SUV to a single light bulb - almost too good to believe.

The authors of An Inefficient Truth point towards The Carbon Neutral Company as their source for the comparison. The folks at The Carbon Neutral Company reference the Feb 2007 Jonathan Koomey paper, Estimating Total Power Consumption by Servers in the US and the World, which identifies the typical power of a medium sized server as 638 watts (2005). Multiply that wattage by 24 hours, 365 days a year, double it to allow for energy required for cooling and apply an average carbon emissions factor for UK grid electricity 0.52kgCO2/kWh. This is compared with an SUV doing 15,000 miles per year and an emissions factor of 2.33kgCO2/litre for gas and the answers come out at about the same 5.7tCO2/yr.

The comparison sounds reasonable.

But that also means that operating an SUV for a year has the same carbon emissions as ten 65W light bulbs (albeit bulbs that are left on all the time). It doesn't sound as bad to say that a server has the same emissions as ten light bulbs as it does to compare it to an SUV. And it is far more credible to have got from 10 bulbs equivalent energy consumption in 2005 to one bulb equivalent in the most advanced computer servers of today.

For the record, BT uses very high proportions of renewable energy and combined heat and power, we have implemented many innovative cooling mechanisms (including not cooling where appropriate!) and use the most efficient servers wherever possible so our emissions are far lower whether your preference is to compare to the light bulbs or the SUV!