Alex Wissner-Gross, a Harvard University physicist, has been studying the environmental impacts of computing, and will soon be publishing substantial research on it. The figures for a Google search were quoted by the UK's Sunday Times.
Where does the carbon come from? From Google's data centers, which are spread out throughout the world. Searches may be sent to more than one data center.
Google disagrees with Alex Wissner-Gross's findings. In the Official Google Blog, the company says that the emissions are much lower, claiming, "In terms of greenhouse gases, one Google search is equivalent to about 0.2 grams of CO2." The company claims that it has among the most energy-efficient data centers in the world, and that
the energy used per Google search is minimal. In fact, in the time it takes to do a Google search, your own personal computer will use more energy than Google uses to answer your query.Wissner-Gross has done other carbon footprint calculations about computer use, and come up with figures worth examining. He says that viewing a basic web page generates approximately 0.02g of CO2 per second. If you view a page with video, animations, or complex images, the carbon footprint rises by a factor of ten, to about 0.2g of CO2 a second.
Yet other people have done other calculations. Here's the most eye-opening, according to the Times article:
Nicholas Carr, author of The Big Switch, Rewiring the World, has calculated that maintaining a character (known as an avatar) in the Second Life virtual reality game, requires 1,752 kilowatt hours of electricity per year. That is almost as much used by the average Brazilian.