Converting Digital Photos Into Tea

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Over on the right, Kiera Butler asks “Are email attachments bad for the environment?” That seemed easy: no. Next question?

But Kiera says yes!

According to Matthew Yeager, a data storage expert who works for the UK data storage company Computacenter, emails — especially those with attachments — still use energy and create greenhouse gas emissions, even if you don’t print them. Last month, Yeager told the BBC that sending an email attachment of 4.7 megabytes—the equivalent of about 4 photos taken on a point-and-shoot digital camera — creates as much greenhouse gas as boiling your tea kettle 17.5 times. I called Yeager to find out the whole story.

Sadly, Yeager didn’t give her the whole story. Over at this blog, however, he credits this figure to a “Life-cycle analysis carried out by [Mark] Mills of Digital Power Group, translated into kettle boilings with help from the Energy Savings Trust [UK].” I tried emailing DPG to get their take on this, but no dice. I haven’t heard back.

But the more I thought about, the more sense it made anyway. Here’s a wild-ass guess at the arithmetic:

  • Let’s figure the average email attachment is sent to ten people and therefore saved ten times. So the total storage used is 47 megabytes, or .047 gigabytes.
  • After surfing around the web, I’d guess that the average power consumption for a storage server is about .2 watts per gigabyte. Big server farms like Google’s use less, your home PC uses more. Older systems use more energy than newer systems. But .2 watts/GB probably isn’t horribly far off.
  • So the power requirement for .047 GB of attachments is .0094 watts.
  • How long are attachments retained? That’s all over the map. Some are deleted instantly, some are saved for a few months, others sit around forever. It all depends on how you (or your corporation) manage email and how it’s backed up. At a guess, let’s say that attachments end up getting saved an average of 3 years.
  • That’s 26,000 hours, so the total energy consumption of our attachments comes to about 247 watt-hours.
  • According to these guys, it takes an electric kettle about 25 watt-hours to boil a cup of water.

So I come up with about 10 kettles, not 17.5. But then again, I didn’t take into account the energy it takes to build and ship the storage servers in the first place. What’s more, when you’re just spitballing like this a difference of 2x isn’t bad. Basically, it shows that the energy consumption of a single email with a few attachments really does add up. Thrilling news, isn’t it?

And one more thing: one of the best arguments for a carbon tax of some kind is that we could stop doing ridiculous exercises like this. The energy externalities would be automatically included in the cost of everything we buy or do, so we wouldn’t have to worry about trying to figure out the most eco-friendly alternative for everything. Wouldn’t that be great?

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