@ecologee wrote to me "Do you know that the SMTP protocol has an overhead of 30%? So it's really inefficient to share large files via email! You can simply test it: take a 10MB-file and mail it to a test-account, the mail size would be around 13 MB."

I found this explanation from Microsoft:

...SMTP uses an ASCII (text-based) format. Because most e-mail messages that are sent are text or Hypertext Markup Language (HTML) messages, very little content conversion needs to be performed on messages...It is important to note that SMTP does require about a 30 percent increase in size for binary content, such as executable attachments, because this content has to be encoded by using uuencode or BinHex. SMTP is not designed to transport large file attachments, because FTP is the preferred method to transport large file attachments. However, in many environments, a 30 percent size increase is acceptable.

This made sense until that last sentence. A 30% increase in file size means a 30% increase in energy consumption and CO2e every day/month/year that message is sitting on a spinning disk. Not to mention the purchase and deployment of more storage gear over time. Making a single copy of an asset available via a collaborative SaaS application or social media site instead of distributing many copies via email is both greener as well as more productive, since it reduces confusion over which copy is the canonic one.

@dcarli asks, "What's the carbon footprint per megabyte stored per month?"

GB is the new MB, so let's look at those.

I have a .5TB NAS device on the office network, rated at 5.6W. I ran the numbers and got ~11 grams of carbon per GB per month, with an electricity cost of 1/10 of a cent.

Of course, I don't know how representative my storage is of the global storage energy profile and a detailed analysis is more complicated.

Our device has a automatic sleep mode, rated at 0.6W. The drive is probably asleep or completely off 12 hours/day, which would cut our footprint almost in half, although this is an unlikely scenario for a 24/7 data center. this is On the upside, I'm not counting the carbon footprint of the backups, which in a data center might happen at least once a day. Or the data center AC. Or redundant storage, if required. Or the carbon footprint involved in the manufacture and ultimate disposal of the device, backup media, etc.

So, for the sake of discussion, let's say that a data center's number would be ~11g times a logical PUE of 1.8 equals ~20g/GB.

20 grams does not sound like much; its all those GBs in the aggregate that generates a lot of carbon. This is the materiality problem, which we saw clearly in the motivational analysis for digital delivery.

According to IDC, the amount of data created and replicated globally in 2008 was ~486 exabytes (~522 billion GB). At 20 grams per GB per month, that is a monthly storage footprint of ~5 million metric tons of carbon, or ~62 million tons/year. ICT is said to account for ~600 million metric tons, which would put storage at ~10%. These are all rough estimates, but give us an order-of-magnitude perspective.