Carbon Footprint of a Download

What is the carbon footprint of a large file download? A paper comparing digital and physical delivery of Microsoft Office is light on detail, but provides some useful clues.

One approach is based on the paper noting that "avoided carbon emissions associated with downloading one copy of Office 2007 are roughly equal to the emissions arising from one gallon of gasoline" and "digital delivery reduced total tonnes of carbon emissions by 88%. Framed another way, digital delivery of Office 2007 is eight times more carbon efficient than producing and shipping a DVD and its associated packaging through traditional retail distribution channels." From this, we can deduce that the emissions of the download are ~12% of a gallon. This includes "the data centers used for hosting software downloads, transfer of that software through the web and even the energy used by a customer’s personal computer to download the Office 2007 program." The EPA puts the CO2e of a gallon of gasoline at 8.8 kg, so we can conclude that the unit footprints are ~1.2 kg (digital) and 10.0 kg (physical)

Another approach is to look at the paper's comments on carbon offsets. From those numbers, we can conclude that the unit footprints are ~0.9 kg (digital) and 7.1 kg (physical).

We're trying to source the exact numbers, but we'll run with ~1.0 kg (digital) and ~8.6 kg (physical)

The 1 kg of carbon per download applies to file sizes typical of movies or large software and games. It is likely that many large downloads will not be this efficient. Click here to find out why, to see a simple chart comparing digital to physical delivery, and to follow a link to the original study.