But there are additional environmental costs to consider as well. For example, the total amount of fossil fuel needed to make a PC is about nine times its own weight - about 240kg. Compare that with a car or refrigerator which only needs about twice their weight.
And once you've made your PC, you've got to run it. So you need electricity - which means more carbon dioxide emissions. Not much electricity for just one PC, maybe 100w, but there are billions of PCs in use around the world today. A leading marketing research company, Gartner, now estimates that that the computing industry is responsible for 2% of global CO2 released into our atmosphere - which puts ICT on a par with the aviation industry.
Between 1980 and 2000, the vast majority of that 2% was caused by the office PC, many of them just idling away in office blocks. Today, the balance of power consumption seems to slipping away from premises-based PCs to whopping great server farms accessed by billions of mobile devices, which themselves chew through vast amounts of precious and rare minerals in their manufacture, resulting in the wholesale purchase of Africa's mineral rights by outside industrial interests, like China. If this trend towards cloud computing continues, data centers could be responsible for up to half of all ICT-related carbon emissions by 2020.
So what this means, in practice, is everything we do online has a carbon price. A single one-hit Google search creates about 0.2g of carbon dioxide. If you go for a more complex search, this can generate between 5g and 10g of CO2 due the unique way Google configures multiple servers to compete in delivering you the answer in less than half a second.
Even browsing a basic website (like this blog) generates about 0.02g every second. For each computer. Every second.
It has even been estimated that maintaining an avatar on a virtual reality site like Second Life consumes about 1,800 kilowatt-hours of electricity per year. By comparison, an average real human on a worldwide basis consumes about 2400kWh per year - so your avatar produces nearly as much CO2 as you do.
Is it just me - or do those clouds in 'cloud computing' begin to look a little more menacing every day?