The internet is generally seen as a "green" technology -- emails can cut down on paper waste, teleconferencing can save on CO2 emitted by flying, and smart grids can help reduce overall energy consumption. But, according to the Guardian's series on carbon footprints, the internet releases about 300 million tons of CO2 each year -- as much as all the coal, oil, and gas used for energy in Turkey and Poland.

The British newspaper acknowledges that carbon footprints are, in general, tough to calculate. However, it arrived at this rough estimate by accounting for the power used up by data centers ("buildings packed top to bottom with servers full of the web pages, databases, online applications and downloadable files that make the modern online experience possible") and personal computing devices. Data centers are one of the less visible factors in understanding the global carbon trail left by our emails, blog trolling, and facebooking, but they are quite significant. A Harvard physicist last year estimated that just two Google searches generate about 14 grams of CO2--or enough to bring a kettle to boil.

A recent UK study determined that in 2005, consumer and commercial information and communication technology (ICT) accounted for about 1.2 percent of fossil fuel emissions. The report predicts that ICT's footprint could climb by 60 percent by 2030.

The Guardian feature highlights some other carbon footprints. Among them:

The Iraq War: 250-600 million tons of CO2 since 2003

The World Cup: 2.8 million tons of CO2 ("more than a billion cheeseburgers")

The 2009 Australian bushfires: 165 million tons of CO2

A banana: 80g CO2 each