Facebook just announced that it now has over 350 million users with half of them logging on to the site on any given day, and the average user spends over 55 minutes a day on Facebook. Plus, 55 million status updates are posted every day and 2.5 billion photos are uploaded each month. Very impressive, but I have often wondered about the environmental impact of social networking. Using carbon footprint as a proxy for overall environmental impact, here is a quick back-of-the-envelope calculation.
The number of user-hours per day is about 160 million (assuming 55 minutes/day/user). I found a CO2 emissions estimate of 20 mg/second for basic web browsing, most of it coming from the electricity consumed by the visitor's computer. I independently verified this by assuming 100 W of power consumption for a typical desktop computer and monitor in active mode, which translates to roughly 20 mg of CO2e per second for US average electricity (cradle to grid). Electricity emissions vary around the world, but the US emission factor is a typical value. For a first-order estimate, I decided to count only the time that users are logged on to Facebook and actively using their desktop computers, ignoring their Facebook activities like status updates, uploads and downloads that will consume additional energy in the network infrastructure and data centers.
Putting all this together works out to 4.2 million metric tons of CO2e per year for all Facebook users. (The actual emissions are likely to be higher, but that depends on a lot of factors ignored here.) This carbon footprint is equivalent to the annual emissions from a million passenger cars in the US.
I know, it is not fair to focus just on Facebook, but I am just using it as an example to understand the footprint of social networking today and how this might change if someday 3-4 billion people end up on social networking sites. I will get back to this topic soon and report on a more rigorous, defensible analysis. For now, this remains a quick-and-dirty initial estimate and a starting point for further exploration.