From Ze Telegraph: A typical search through the online giant's website is thought to generate about 7g of carbon dioxide. Boiling a kettle produces about 15g.
The emissions are caused both by the electricity required to power a user's computer and send their request to servers around the world.
The discovery comes amid increasing warnings about the little-known environmental impact of computer and internet use.
According to Gartner, an American research firm, IT now causes about two per cent of global CO2 emissions and its carbon footprint exceeded that of the world's aviation industry for the first time in 2007.
Dr Alex Wissner-Gross, a physicist from Harvard University who is leading research into the subject, has estimated that browsing a basic website generates about 0.02g of CO2 for every second it is viewed.
Websites with complex video can be responsible for up to 0.2 g per second, he believes.
On his website, CO2stats.com, Dr Wissner-Gross wrote: "Websites are provided by servers and are viewed by visitors' computers that are connected via networks.
"These servers, clients and networks all require electricity in order to run, electricity that is largely generated by burning fossil fuels like coal, oil and gas.
"When fossil fuels are burned, carbon dioxide is released into the atmosphere, which contribute to climate change.
Dr Wissner-Gross believes that Google's unique structure - which sees it send searches to multiple servers around the world and give which ever response is returned quickest - causes its searches to produce more emissions than some other sites.
He told a newspaper: "Google operates huge data centres around the world that consume a great deal of power.
"A Google search has a definite environmental impact.
"Google are very efficient but their primary concern is to make searches fast and that means they have a lot of extra capacity that burns energy,"
A separate analysis by John Buckley, of carbonfootprint.com, a British environmental website, put the CO2 emissions of a Google search at between 1g and 10g.
Chris Goodall, the author of Ten Technologies to Save the Planet, said that assuming the user spends 15 minutes on their computer, the carbon emission of a Google is between 7g and 10g.
Google claimed that the number was "many times too high" and one Google search is equivalent to about 0.2 grams of CO2.
A spokesman for Google said: "We are among the most efficient of all internet search providers."