Describing his research in the Sunday Times, the Harvard academic said that despite Google's secrecy over its carbon footprint, he had calculated on the basis of publicly available information that each Google search generates an estimated 5-10 grams of CO2. The newspaper reported that two Google searches releasing 7g of CO2 were almost the equivalent of boiling a kettle for a cup of tea. Wissner-Gross later said his work was focused on the web overall, and the example of tea kettles was not one of his.
The scale of the search engine's carbon footprint is due to the fact that the request is sent to multiple servers across the world, but only the quickest response reaches the user, according to Wissner-Gross.
"Google isn't any worse than any other data centre operator. If you want to supply a really great and fast result, then it's going to take extra energy to do so," he told the BBC.
Google, which is keen to promote its image as a green company, dismissed the figures as "many times too high". It claimed on its official blog that a typical search returning results in under 0.2 seconds amounts to about 0.2 grams of CO2.
"We've made great strides to reduce the energy used by our data centres, but we still want clean and affordable sources of electricity for the power that we do use," the internet giant stated, referring to a $45 million investment in breakthrough clean energy technologies in 2008.
On average, every second spent browsing the web produces 0.02g of CO2 per second, according to the study. Wissner-Gross emphasised that as the amount of animations and video content increases, the number can be as high as 0.03g every second.
According to the physicist, the electricity consumption of the computer must take most blame for the carbon footprint of a "typical website experience", followed by the network infrastructure that transmits the website. The servers hosting the website are the smallest contributors, he said. His analysis of the Office of the UK Prime Minister's website on Saturday 10 January showed that it had been only operating at 64% of its network energy efficiency, while the efficiency of the busy BBC News website was only 49%.
Gartner, an information technology research company, estimated in 2007 that the IT industry was already causing 2% of global CO2 emissions, the equavalent of the carbon footprint of the entire global aviation industry.
The EU is currently planning to introduce energy-efficiency standards for the ICT sector to fight climate change and reduce energy waste (EurActiv 12/12/08). The Commission is expected to publish policy recommendations after an industry report dated June 2008 argued that the industry's impact on the climate would grow rather than diminish if measures were not taken (EurActiv 27/06/08).