The carbon footprint of a search query is nowhere near the estimate concluded by a Harvard academic, Google said late Sunday.
British newspaper The Sunday Times published a story on Sunday with results from a study conducted by Alex Wissner-Gross, a physicist who estimates a Google search generates 7 grams of carbon dioxide (CO2), slightly less than half as much CO2 as boiling a kettle for a cup of tea.
Wissner-Gross maintains that it shows a Google search has "a definite environmental impact."
Google, however, is arguing 7 grams is way off and is trivial compared to other CO2-spewing activities, such as driving.
One search query releases the equivalent of 0.2 grams of CO2, wrote Urs Hölzle, Google's senior vice president of operations on a company blog late on Sunday.
It's difficult to see how either Wissner-Gross or Google come to their conclusions since no technical detail is provided.
However, the disparity may come from the fact that Google and Wissner-Gross are measuring different things. The Sunday Times story says the researcher's study covers a search query from a desktop computer, which could include the emissions caused by running that PC. Google's response focuses on the data center.
Wissner-Gross's study is due for release soon by the U.S. Institute of Electrical and Electronics Engineers, according to the Times.
Google estimates one search, including a share of the energy spent building the search engine's index, uses 0.0003 kWh of energy, or 1 kilojoule. An average person's body consumes around 8,000 kilojoules of energy a day, and so one search would use the same amount of energy a person burns in 10 seconds, Hölzle wrote.
The energy consumption of a search query pales in comparison to vehicle travel, Hölzle wrote. The European Union standard for vehicle emissions is around 140 grams of CO2 per kilometer driven, so most cars generate enough CO2 for a thousand Google searches just traveling one kilometer, Hölzle wrote. Google said in the past people would have often had to drive to a library to find information.
Google and other major technology companies such as Microsoft have sought out sites for new data centers located near cheap hydroelectric power in order to reduce their own energy costs. Server manufacturers have also tried to reduce the energy consumption of their products.
"We've made great strides to reduce the energy used by our data centers, but we still want clean and affordable sources of electricity for the power that we do use," Hölzle wrote.
In October, Google revealed internal test results on power consumption in its data centers.
Google uses a metric called Power Usage Effectiveness (PUE) to gauge its data center efficiency. PUE is a ratio of the total power consumed by a data center to the power consumed by all of the IT equipment used in the facility. A PUE of 2.0 shows that for every watt powering IT equipment, one watt is used to cool and distribute power to the equipment.
The U.S. Environmental Protection Agency estimated in 2006 that typical data centers have a PUE of 2.0 or higher, but that figure would drop to 1.2 by 2011 due to new cooling techniques. Google said that its PUE average now is around 1.13.
That efficiency has been gained by using more efficient power supplies, efficient voltage regulators on motherboards and by designing server racks to use as little fan power as possible, Google said.
Estimates put the IT industry's greenhouse gas emissions around 2 percent of the world's total, about equivalent as the airline industry. But technology companies have come under increasing pressure from environmental organizations and consumers to become more conscious about emissions and other issues such as equipment disposal.