Some people had claimed that each search used absurdly high amounts of energy, and produced 7 grams of carbon dioxide. Google has responded by saying that that's just not true:
Good job to Alex Wissner-Gross from Harvard who started this conversation in the first place, and good job to Google - both for responding transparently, and for taking the environment seriously. They not only build efficient data centres, but they co-founded the Climate Savers Computing Initiative.
Recently, though, others have used much higher estimates, claiming that a typical search uses "half the energy as boiling a kettle of water" and produces 7 grams of CO2. We thought it would be helpful to explain why this number is *many* times too high. Google is fast — a typical search returns results in less than 0.2 seconds. Queries vary in degree of difficulty, but for the average query, the servers it touches each work on it for just a few thousandths of a second. Together with other work performed before your search even starts (such as building the search index) this amounts to 0.0003 kWh of energy per search, or 1 kJ. For comparison, the average adult needs about 8000 kJ a day of energy from food, so a Google search uses just about the same amount of energy that your body burns in ten seconds.