There’s nothing like being specific, and being persistent. Last year, environmental campaigner Greenpeace asked Facebook to stop using coal-fired power in its power stations; this year, it’s back on the subject. And this time it’s setting a deadline.

Greenpeace has asked Facebook to commit, before Earth Day, to stop using carbon-fired electricity within ten years. For nearly a year, Greenpeace has been asking cloud operators and social networks to clean up their IT acts, but has focused on Facebook since last September, as the biggest and most obvious target.

In 2010, Facebook opened a data centre in Prinveille Oregon, which uses electricity, 58 percent of which is generated by coal. According to Greenpeace. It will use 30-40MW – the equivalent of more than 30,000 US homes.

If a user that big refused to buy dirty electricity, Greenpeace says, it would make a difference to the fortunes of the dirty generators. And Facebook’s next data centre, in Forest City, North Carolina gets more Greenpeace flak because it will use 50 percent coal and 39 percent nuclear power (Greenpeace doesn’t like nuclear power either, though it is low-carbon).

Facebook: low PUE isn’t low carbon

Facebook is upset. It has pointed out that its data centre in Oregon is a very efficient one with a PUE (power usage effectiveness) of 1.15, because it is in a temperate region and no chillers are necessary.

It might also argue – but hasn’t so far – that it has a duty to keep its costs down. If it paid more for clean electricity, it could argue, the cost would have to be passed on to consumers, who currently get its service free (or at the price of seeing very annoying adverts and suffering grudging-to-poor security).

However, PUE is not the end of the story on carbon footprint. It just measures how efficiently the data centre feeds its electricity to the IT equipment. The “carbon intensity”, the amount of  CO2 released in making the electricity, is a more significant factor, according to an interesting blog from Liam Newcombe of Romonet – an ace contributor to the webinar on carbon reduction that I recently chaired.

The UK’s electricity supply has a carbon intensity of 0.5kg of CO2 per kWh of energy generated. This is low compared with other places like Oregon, because the UK has a mix of generation including a lot of fossil fuel, nuclear power and some renewable energy.

Oregon’s carbon intensity will be higher (maybe as much as 0.8) as it uses more coal, while other countries like the Netherlands have a lower carbon intensity, perhaps as low as 0.3.

If the data centre was perfect, with a PUE of 1, you’d just see the blue bars in Liam’s graph. The inefficiencies in the data centre add the red part to the electricity going to the IT kit.

The left bar shows a data centre with a PUE of 1.5 in the UK, while the one next to it is something like Facebook’s Oregon data centre – a much higher carbon intensity in the power supply, and smaller percentage added.

The end result is that in Oregon, even a 1.2 PUE data centre (a sliver less efficient than Facebook’s) would have a bigger carbon footprint than one in the UK, with a fairly average 1.5.

And even worse for people who swear by PUE, if you are in the Netherlands you can run a data centre with a rather poor PUE of 2.0, and still come in with a lower carbon intensity than the UK.

It’s this sort of consideration that has led the Green Grid to propose CUE, as a measure of the carbon intensity of a data centre.

Putting the efficiency cart before the carbon horse

So, on the face of it, Facebook’s justification is putting the efficiency cart before the carbon intensity horse.

But there is more to it. How efficiently is that electricity being used once it gets to the servers? How many instructions does it power? And how efficiently are those CPU instructions used to do actual work?

And, if you want to push this to the limits, how much value is there in that work, however efficiently it is being carried out?

There are those who might argue that Facebook’s entire output is a waste of time – well, eWEEK readers seem to think so). The people of Egypt and Tunisia, and other countries where Facebook has been used as a tool for public protest, might disagree. If Facebook really emerges as a valuable forum for social change, then it can justify a certain carbon footprint.

That’s certainly what Greenpeace would say about its own servers. It’s been pointed out that the environmental group uses some servers which are powered by coal-fired electricity, but the group would probably say that no-one has a zero carbon footprint, and its work balances that out.

The simple-minded answer to this would be to suggest that all servers are moved to Iceland, or another country where the grid has a low carbon intensity. But the simple answer may well be wrong.

As always, there is more to this than meets the eye.

Peter Judge

Peter Judge has been involved with tech B2B publishing in the UK for many years, working at Ziff-Davis, ZDNet, IDG and Reed. His main interests are networking security, mobility and cloud

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