To find out if avatars have a carbon footprint at all, we need to look at servers. Boring square boxes with expensive components that runs our world. If you don't love the look of a data-center in the dark, feel free to jump to the conclusion at the bottom:-)
The main component in a server is the CPU/Processor. It's the closest thing to a brain that a computer has. Back in the dark ages of the beginning of the PC era, a CPU was only capable of thinking of one task at a time (some say that's typically male:-) ). Todays processors have several "cores", that is, they are capable of running several tasks at the same time, thus somehow acting like several processors on one chip (not unlike some woman I know....).
The Second Life server software runs one full region per dedicated CPU core, while 3 homesteads or 4 openspaces shares a core. Doing some simple math, we find that the grid as of today demands 24.500 CPU cores. In addition, there are database clusters, inventory servers, login servers, web servers, development servers, the aditi test grid, and so forth. To keep it simple, we estimate 5.500 cores for these, giving us a need of 30.000 CPU cores.
A modern server deploys 2 6-core CPUs in a 1U rack mounting for a total of 12 cores per server. This gives us a need for 2.500 servers. To be able to visualize the volume of servers: 2500 servers needs 55 full-height racks, or a row of lockers around 30 meter long.
A typical "pizza-box" server - the hei1ght is commonly measured in U - this is a 1U server holding 12 full sims!
Alternatively, 2500 servers is about the equivalent of a so-called "cloud container" - a kind of superserver installed in a housing the size of a 40 foot container, designed for huge datacenter usage. One interesting aspect of these containers is that they are designed for out-door operations, to get the benefit of free cooling. So, next time you encounter a 40 feet container (the long ones), you can think that as of today, this is the smallest box our world can fit into.
Unfortunately, most of Second Life probably runs on older servers, perhaps with just dual core CPUs, making it a potential total of 7.500 servers or 170 racks in an 85 meter row..
7.500 servers each taking 200 watt power and 200 watt cooling consumes 3 million watt, or 26 million kWh per year. Thats a lot of power, but it's actually a lot less that the viewers! If we assume a mean login concurrency of 60.000, each running on a PC consuming on average of 150 watt, we must add a whopping 79 million kWh per year for a total of 105 million kwh per year.
That's the equivalent of 5200 average Norwegian households, or a bit less than 20.000 people. Considering that second life is the home of more than 500.000 avatars logging in at least once every week, this means that an avatar consumes just 4 percent as much power as a human being, or about 210 kWh/year. Add to this the fact that an avatar seldom drives a car, and when they do it's always a zero-emission vehicle, so maybe it's not too bad:-)
According to this report, the mean carbon footprint per kWh in the US was 1.4 pounds in 1999. Converting to metric, it gives each avatar an average carbon footprint of 133kg/year, or 0.15 metric tons. To visualize that, my medium-sized car, running 20.000 km/year, has a carbon footprint of 4.55 metric tons.
An avatar has a carbon footprint of 0.15 metric tons a year!
So yes, an avatar actually have a measurable carbon footprint, but fortunately it's a lot less than us human. For me, using the my bike just 2 km/day instead of the car would offset my avatars carbon footprint (not to mention giving me a body he would envy me lol). Anyone up for that challenge?