Yesterday Y Combinator backed CO2Stats announced the launch of a fully functional version of their emissions measuring service for websites. The launch comes nearly a year after the release of a prototype widget that was designed to test the market and gauge user response. The idea eventually attracted enough press and positive feedback for the founders to take their service and calculations to the next level.CO2Stats makes a website “green” by calculating its environmental footprint and buying green power (i.e. wind, solar) elsewhere on the grid to compensate. The service calculates not only the energy used to power a site’s server, but also the power used by client machines visiting the site. It turns out that visitors actually consume more power than the servers themselves.The methodology for calculating energy consumption is extremely rigorous, as it must be for something like this to be accepted. The system takes into account geographic location of a site’s servers and visitors, time spent on a site, client device type (mobile, laptap, etc), and even the size of the page window on the user’s screen.Sites supporting the service sport a clean energy badge that, when clicked on, displays CO2 emissions resulting from visitors, servers, and the network, along with a breakdown of the fuel types used to power the site and where the power was generated.CO2Stats charges a flat rate that is dependent on the cumulative amount of power they spot their clients. This ensures that sites aren’t punished for peaks in traffic, and makes the idea more attractive to sites with a large userbase. The service could make it big if it becomes standard practice for companies to maintain a “green” web site. Electricity generation required for information and communication techologies is currently responsible for 2% of global CO2 emissions, and this number is only growing. Current clients include Gazelle, and a number of environmental awareness sites.