Watching another episode on Netflix, reading The Guardian online and downloading apps are not obvious ways to pollute the atmosphere. But collectively, our growing appetite for digital services means the data centres that power them are now responsible for about 2 per cent of global greenhouse gas emissions, a similar share to aviation.
Varying from a small room with servers to vast farms with a floor area of 150,000 sq m, data centres are big energy users. As well as requiring power to run the equipment that stores and serves us cloud computing and on-demand music, films and entertainment, those servers also generate a lot of heat, and require huge amounts of energy to keep them cool. That's why big data users such as Facebook are siting their centres in cool climates such as northern Sweden.
Individually, our everyday browsing has a relatively minuscule impact. Google, in response to claims that each search on its site generated as much CO2 as boiling half the water for a cup of coffee (7g), calculated that the true figure was much lower, at 0.2g. Watching a YouTube video of cats was higher - 1g for every 10 minutes of viewing - while using Gmail for a year produced about 1.2kg per user.
Not to be outdone, Facebook also put a figure on its average user's annual footprint - 269g of carbon dioxide, roughly equal to the carbon footprint of a cup of coffee.
But with the technology giants' billions of users worldwide, those numbers add up quickly. Google's carbon footprint was 1,766,014 tonnes of CO2 equivalent in 2013, and the bulk of that was from data centres.
As with emissions from air travel, the real issue with data centres is the rate at which they are growing.
"It's an exponential growth in data," said Ms Sophia Flucker, director at Operational Intelligence, a Britain-based consultancy that advises data centres on their energy use.
"Although IT efficiency is improving, and we can do more with less power, the demand is still there," she said. "Any efficiency gains are being eaten up by demand. It's very much an upward trajectory."
The industry claims improvements in energy efficiency and technology mean it can "decouple" economic growth and emissions, so that it could keep growing, while keeping the sector's share of global emissions in 2030 at roughly the same as they are today.
But Greenpeace, which has reported for several years on data centres' environmental performance, says energy efficiency improvements can only do so much. How tomorrow's data centres are powered is key when it comes to climate change, it says.
"Energy efficiency is, of course, very important," said Mr Gary Cook, senior IT analyst at Greenpeace. "It's critical. It's also completely insufficient on its own. If you look at the growth in data centre demand and our digital world, energy efficiency will slow the (emissions) curve, but the curve is still going to the moon."
He said data centres could become either a villain as an increasing source of emissions, or a driver for the take-up of clean energy sources, such as wind and solar.
"If they're built in the right way, it could be a great story and help the transition (to renewable energy). If they're built in the wrong way, it's going to take us in the other direction, and increase our dependence on the sources of energy we have to move away from to address climate change."
Courtesy of The Guardian, a member of the Climate Publishers Network. The network is a content-sharing partnership among international news publishers, including The Straits Times, on climate change stories ahead of the 2015 UN climate summit in Paris.
