One of the recently released widget plugins for WordPress lead me to a site called CO2Stats.com. Basically, you get a little scrap of code to insert into your blog (or any other type of website for that matter). When people visit your site, they cause a contribution to be made to renewable energy projects that help offset the CO2 they estimate running your blog causes to be emitted. The people at CO2Stats did some calculations and determined that the global average rate of carbon emissions due to the electricity consumption of a single personal computer interacting with a server is 17 mg of CO2/second. That is then used in a calculation involving the number and duration of visits to a website to calculate the total emissions for a site. The offsets are funded by advertising sponsors who are committed to making the Internet a little more environmentally friendly.

An entry in the Boston Herald Green World blog has an interview with the people behind CO2Stats.