We know that computers and related gear consume a lot of electricity. What we don’t know, with any precision, is what “a lot” is. Earlier this year, the Lawrence Berkeley National Laboratory conservatively estimated that running corporate server computers, and keeping them cool, accounted for about 1.2% of total electricity consumption in the United States in 2005. That’s equivalent, the researchers said, to the output of “about five 1000 MW power plants.” (The study excluded the hundreds of thousands – possibly millions, at this point – of custom-built servers that Google operates.)

Corporate servers, though, are just one component of the global computing grid. Now, as Slashdot notes, a journeyman researcher named David Sarokin has taken a crack at estimating the overall amount of energy required to power the country’s computing grid. He combines the Berkeley numbers on server consumption with estimates from other recent studies of the power used by PCs, networking gear, and the telephone network. The numbers, in billions of kilowatt-hours, break down as follows:

Data center servers: 45

PCs and monitors: 235

Networking gear: 67

Phone network: 0.4

That amounts to about 350 billion kWh a year, representing a whopping 9.4% of total US electricity consumption. On a global basis, Sarokin estimates that the computing grid consumes 868 billion kWh a year, or 5.3% of total consumption.

These are, it’s safe to say, rough estimates. Each of the studies Sarokin draws on makes various assumptions of greater or lesser reliability – and Sarokin adds a few assumptions of his own. Still, even if they’re just in the ballpark, his numbers underscore the huge amount of electricity that our modern reliance on computing and the Internet demands. It’s worth noting, moreover, that Sarokin’s study appears to overlook some related sources of power demand – not just custom-made servers but data center components beyond servers and air-conditioning, various peripherals such as printers and scanners, and all the devices that we’re always recharging and that increasingly draw on the Net, from BlackBerrys to iPods to iPhones.

Despite the increasing attention being paid to computing’s vast energy requirements, most companies remain more or less oblivious to how much power their own IT operations are using. According to a report on a survey of top IT executives issued yesterday by the Economist Intelligence Unit (and sponsored by IBM, which has a commercial stake in the issue):

Most IT executives say that their firm does not monitor its IT-related

energy spending (and a further 9% don’t know) [and] only 12% of respondents believe that the energy efficiency of IT equipment is a critical purchasing criterion.

“Although concerns about energy efficiency and global warming are now high on the political agenda, the spotlight has not yet been turned onto the IT function,” observes the report’s editor. That is sure to change as the public becomes more aware of computing’s oversized carbon footprint.