As people turned off the lights for Earth Hour and pondered their electricity use, one of the world's most rapidly growing power guzzlers for which nearly everyone carries responsibility is largely hidden from view.
It's the network of data centres and their servers that are the invisible backbone of the Internet. The popularity of all the twittering, blogging, music downloading, and Facebooking has had a little-known environmental downside, by boosting the demand for electricity to run these centres.
The vast, worldwide scope of the Internet makes it difficult to calculate just how much power the Web and its related activities consume, but the amount is substantial and has become the subject of studies in scientific journals.
Most of the researchers pondering the question of this power usage have focused on data centres and their servers. These centres are enormous energy gluttons, with the servers consuming so much energy they're always at risk of overheating, so companies have to spend about as much on electricity to air-condition the devices as they do running them.
While a person sitting behind a computer realizes they're using electricity, that's only the beginning of the power consumption story.
Ask Google to do a search and follow it up by clicking the link, or post a blog, and you're relying on servers and their stores of data and applications.
Servers are non-descript pieces of electronic hardware, each about the size of a pizza box. They typically consume about 200 watts of electricity apiece, or about the same amount needed to run 13 compact fluorescent light bulbs.
While one server has modest power demands, there is so much Internet activity that millions of them are needed. At data centres, servers are stacked in cabinets like CDs in a storage rack. A typical data centre has about the same floor space as 15 monster homes, and thousands of servers.
The concentration of many servers in one place is the reason they need so much air conditioning. When they're operating, servers collectively generate waste heat, so a constant flow of cool air around them is required to keep them from being damaged by overheating.
U.S. researcher Jonathan Koomey from California's Lawrence Berkeley National Laboratory has done some of the most extensive calculations on electricity use at data centres, and estimated that they accounted for about 1 per cent of total world electricity consumption in 2005, according to a paper he authored last year that appeared in Environmental Research Letters.
Given all the conventional uses for electricity, such as running everything from toasters to televisions and subways, the 1 per cent is a big deal.
It's a growth in demand that has come out of nowhere, and equals the amount of power produced by 17 large, coal-fired generating stations.
Another way of viewing the demand is that the world's data centres consumed about the same amount of electricity as about 10 million typical Canadian homes.
But that isn't the end of the story, because the electricity demand isn't static. Thanks to the rising popularity of fads such as twittering and Second Life, power use is surging.
The total cost of electricity needed to run the world's growing server fleet has been projected to rise by a compounded rate of about 11 per cent a year from 2005 to 2010, according to IDC, a Massachusetts-based firm that tracks Internet trends. It said the electricity bill to power and cool the world's servers should reach a stupendous $44.5-billion (US) next year.
While ordinary consumers are aware of just how much electricity they consume because of their monthly power bills, they don't see the amount they're responsible for on other parts of the Internet. It's embedded in the price of consumer goods and hidden in corporate expenses.
Given the huge amounts of power drained by the centres, companies are on the hunt for ways to make them more energy efficient.
One way has been to develop software that analyzes the layout of the centres to see if there are better ways to configure the servers to minimize the air conditioning. This approach has cut air conditioning usage by about 25 per cent, in some cases.
Still, the proliferation of blogs and Facebook postings and all the information that clutters the Internet has to be hosted somewhere.
Even the effort to have a new .eco Internet domain set up, an idea that has been backed by anti-global-warming campaigner Al Gore's group, Alliance for Climate Protection, would exact an environmental price.
Some people see the .eco domain as a boon because it would allow environmental businesses or activist groups to identify themselves more easily. While this might be a laudable goal, it would require extra server capacity somewhere in a data centre.