Significant impact for a supposedly virtual world
Nicholas Carr wrote about how much electricity does a Second Life citizen use in a year, trying to estimate the electricity consumption per virtual citizen. It comes out close to the Brazilian average (note this is just electricity, not considering cars, heating oil, etc). Translated in terms of CO2 production, it comes to 1.17 tons of CO2 per virtual citizen (a total of 14,763 tons overall), equivalent to driving an SUV for 3,700 kilometres.
It has been pointed out that the consumption of the users' computers is not taken into account, and that the amount of power needed for cooling has been underestimated as well.
Someone commented that using rates commonly found in Texas, it would come out to about $1,500 per server annually, so it's not only environmental, this also comes down to real money. This, I find very encouraging, because it has the airs of a concrete implementation of true-cost economy. Even though it's really far from being true-cost, it gives a plain old capitalist incentive to go easy on the environment that's becoming harder and harder to brush aside.
When you buy appliances these days, you generally see a label rating their energy consumption relative to other devices in the same class, and I don't know about people in general, but I try to pick the A or A+ models, not only because it's the right thing to do, but for the rather self-centered reason that it'll be easier on my bank account.
I hope to see something similar for computers, and hopefully see people and businesses favour environmentally (and thus, financially) friendlier machines.
Epilogue: Think of the World of Warcraft servers now.