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A recent post on Google’s Official Blog explained how, thanks to their power-saving and energy efficient data centers, the environmental impact of a Google search is significantly lower than some have recently speculated.

Harvard University professor Alex Wissner-Gross authored a report analyzing the environmental costs that Internet browsing and performing Google searches, according to which even just browsing a basic Website can generate about 0.002g of CO2 for every second it is viewed, while sites with complex video can bring even more CO2 in the atmosphere, somewhere around 0.2g per second.

Wissner-Gross, an environmental researcher and activist, has submitted his research for publication by the US Institute of Electrical and Electronics Engineers and has also set up a site, CO2stats.com, that helps webmasters reduce their websites’ impact on global warming by making their code more efficient and their site faster to load.

Many independent and similar studies on the matter had preceeded the one published today: an estimate from John Buckley, managing director of CarbonFootprint.com, a British environmental consultancy, puts the CO2 emissions of a Google search at between 1 and 10 grams, depending on whether the PC has to be started or not, while simply running a PC generates between 40 and 80 grams per hour.

Chris Goodall, author of “Ten Technologies to Save the Planet”, estimates the carbon emissions of a Google search to be somewhere between 7g to 10g assuming at least 15 minutes of computer use; but the most impressive data comes from Nicholas Carr, author of “The Big Switch” and “Rewiring the World”, according to whom maintaining an avatar in the Second Life virtual reality game requires 1,752 kilowatt hours of electricity per year, almost as much as the average Brazilian person consumes in a year.

As many have noted, such data can be very effective in highlighting the disparity in the energy distribution around the world; some attention also has to be directed at the fact that energy consumption by computers has been growing rapidly in the last few years, and the rate of growth is increasing as well.

Just hours after the initial publishing of thw Wissner-Gross report, Google responded to the accusations with a blog post, saying the study was flawed and that the actual emissions were much lower than the professor’s estimates.

“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,” said Urs Hölzle, Senior Vice President of Operations at the company.

According to Google, in fact, the average query only takes 0.20 seconds to complete, with an actual server elaboration time that is no greater than 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,” the blog post explains.

Google says that, as a consequence, one of its searches only equates to about 0.2 grams of CO2, significantly lower than the Harvard study released today is suggesting. Professor and author of the study Alex Wissner-Gross justified his estimates by saying that the company is overall very efficient, but “their primary concern is to make searches fast, and that means they have a lot of extra capacity that burns energy”.

More information on Google’s datacenters, including their energy and recycling policies, can be found on this page.