Harvard University physicist Alex Wissner-Gross claims a typical search query on Google produces about 7g CO2. His study suggests two Google searches on a desktop PC produces 14g of CO2, which is roughly the equivalent of boiling an electric kettle.
Although the American search engine is renowned for returning fast results, Dr Wissner-Gross says it can only do so because it uses several data banks at the same time.
Speaking to the BBC, he said a combination of clients, networks, servers and people's home computers all added up to a lot of energy usage.
"Google isn't any worse than any other data centre operator. If you want to supply really great and fast result, then that's going to take extra energy to do so," he said.
More info at BBC News. Google disputes Wissner-Gross' figures and claims a search generates only 0.2g of CO2.