Internet responsible for 2 per cent of global energy usage

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How much energy does the internet use? It's hard to know where to start. There's the electricity consumed by the world's laptops, desktops and smart phones. Servers, routers and other networking equipment suck up more power. The energy required to manufacture these machines also needs to be included. Yet no one knows how many internet-enabled devices are out there, nor how long they are used before being replaced.

That hasn't stopped Justin Ma and Barath Raghavan from trying to answer the question. The pair, researchers at the University of California, Berkeley and the nearby International Computer Science Institute respectively, estimate that the internet consumes between 170 and 307 GW. Which, of course, raises another question: is that is a big number, or a small one?

Raghavan and Ma came up with their total by conducting a rough internet census. By drawing on previously published research, they estimate that our planet is home to 750 million laptops, a billion smart phones and 100 million servers.

They also put figures on the energy that it costs to produce each of these devices (4.5 GJ and 1 GJ for a laptop and smartphone respectively) and the period for which each is used before being replaced (three years for a laptop, two for a smart phone). Estimates for the energy that cell towers and optical switches use when transmitting internet traffic, plus similar calculations for wi-fi transmitters and cloud storage devices, helped complete the picture.

Their final answer sounds big. A gigawatt is a billion watts, so running and maintaining the internet is like illuminating several billion 100W bulbs simultaneously. But it's a small number compared with global energy use across all sectors. That figure is 16 terawatts, so the internet is responsible for less than 2 per cent of the energy used by humanity.

Raghavan and Ma suggest that attempts to create more energy-efficient internet devices, while worth pursuing, will not do much to lower global energy consumption. Instead, they propose that we should think about how the internet can replace more energy-intensive activities. Their calculations show that a meeting that takes place by video-conference uses an average of one hundredth as much energy as one in which participants took a flight so that they could sit down together. Replacing just one in four of those meetings by a video call, they add, would save as much power as the entire internet consumes.