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Even if you're not buying or disposing of equipment, there are measures you can take to reduce your carbon footprint. For a start, you can manage the way you or your company use power. A report by the National Energy Foundation in October estimated that the 1.7 million employees who don't turn off their PCs at the end of the day contribute about 700,000 tonnes of CO2 emissions every year - equivalent to the annual emissions of 120,000 "Chelsea tractors" or the exhaust emissions of a city the size of Liverpool. This isn't only helping to turn Torquay into a Mediterranean hotspot, it's also costing your business an extra £9 per employee per year in electricity bills.

The best solution is to switch off at the plug, but you should also enable power-management settings. If you're familiar with the BIOS, make sure S3 suspend mode is enabled too, as this is much more power efficient than the traditional S1 - though beware that not all hardware is S3 compatible. At the absolute least, switch off the screen when it's not in use. The National Energy Foundation (NEF) recommends setting Windows power management to switch off a display after 20 minutes of inactivity, and do so in preference to using a screen saver, which uses as much power as the Windows Desktop, or even more if it's a GPU-intensive 3D demo. This isn't always practicable - in some financial sector jobs, employees may need a constant update on the screen without physically interacting with their computer - but where it's possible it's common sense.

However, switching off the whole system is markedly better. Some naysayers disagree, but let's have a look at their arguments:

Switching off will damage the PC or your data

No it won't. The boot and shutdown processes don't put any significant strain on the PSU or the major components, and modern hard disks are designed to park the head safely away from the surface of the platter when the drive is powered up or down.

Updates should be installed overnight

First, how often do you really need to do this, and couldn't you just use Wake-on-LAN facilities or arrange to leave systems on just one night a week? These days, the processing impact of anti-virus and security updates is minimal, so there's no reason why updates and scans can't take place during the day. And if you have dual-core CPU systems, there's no excuse.

Startup wastes valuable work time

If a system takes longer than a minute to boot, it needs looking at - either it's being dragged down by helper applets that need removing, or there's malware knocking around. And how valuable is one minute on the average working morning, anyway?

If you're rolling out new systems using Intel's vPro technology, powering down makes even more sense. First, vPro systems have a remote communication channel that enables system administrators to switch on, repair or update, then switch off a PC remotely - even if the unit has been powered off (provided it remains plugged in). Second, vPro systems are designed to take advantage of virtualisation, meaning you can use the power of a Core 2 Duo system to run virus scans, anti-spyware applications, system updates and backups on a virtual appliance without the user being aware it's going on.

If you can, automate shutdown processes using the Windows Power Management control panel and either lock out or educate users so they don't change the settings. The NEF also recommends appointing someone to be the "energy champion" of the office, giving them the authority to switch off equipment and check power consumption. It even suggests empowering cleaners to switch off unused displays (although having them power down PCs isn't a good idea).

Finally, encourage the users to get into the habit of switching off printers, scanners and the like at home time; we may live in a 24/7 work culture, but a laser printer in standby mode is consuming between 15 and 70W (although a few models go down to as little as 2W). Also, watch out for those people who habitually leave a mobile phone or PDA charging all day, every day. Not only is it an inefficient way of using their batteries, it also means the chargers are constantly draining power.

At home

Similar measures apply just as well at home. Power down your system when not in use and don't run a screensaver: set power management to power down your monitor instead. Don't leave phones, cameras or PDAs charging constantly, and if you're waiting for a large download or a system update to run overnight, at least turn off your monitor. Energy consultant Catriona McAllister also adds that you should think about avoiding distributed computing initiatives. While your participation may bring societal benefits (or at least discover life near Alpha Centauri) "these can result in PCs consuming above-average consumption and can sometimes require PCs to be left on 24 hours a day".

In addition, take a look at your peripherals. Do you really need to have a 5.1 speaker set, a scanner and a printer switched on constantly, even when you're just browsing Ebay? Then switch them off. If you're a gamer, consider using headphones instead of a big speaker system - you'll not only save energy, you'll make less noise and probably benefit from a more immersive gaming experience.

Also, switch off your router when you're not using your internet connection. It's still drawing power while it waits for a device to connect and, contrary to some opinions, switching off can help maintain a solid connection (many ADSL providers now recommend switching off and resynching the connection, particularly on 8Mb ADSL Max connections, which can get "stuck" at absurdly low data rates).

To make things easy, have everything plugged into one power-strip (with a surge protector to protect it) and switch it off at the end of the day. You could try our recommended OneClick Intelliplug and Intellipanel products (www.pcpro.co.uk/reviews/88759), which automate the switching off and on of attached peripherals when you power up or down your PC.

Last but not least, look at ways of making your PC more energy-friendly. If you have a CPU that supports Intel's SpeedStep or AMD's Cool n'Quiet technologies, then install the appropriate drivers. That way, you'll still have performance when you need it, but the CPU will throttle down and consume less energy during simple applications. You could also look at changing your PC's power supply. However, it isn't its watt rating that's crucial, but its efficiency. Though in most cases a 500W supply will probably waste more energy than a 350W supply, it should theoretically only consume the power it needs, meaning if you have the same components, the actual rating of the PSU won't make a vast difference.

However, some PSUs are far more energy-efficient than others, and waste significantly less energy as heat. Look for one branded as being 80% efficient or more (check www.80plus.org for details) and you can cut down your CO2 emissions and save yourself additional money on your electricity bill.

Managing your consumables

But energy consumption is only part of the picture; responsible computing also means thinking about how you use and dispose of consumables - inkjet cartridges, laser toner, batteries, optical media and the rest. While for the most part these items aren't toxic themselves, they still contribute to the mountains of waste that end up in landfill every year and employ valuable resources that could be reused.

For a start, if you or your business uses inkjet printers, think about investing in more efficient technologies. As we saw in our April 2006 inkjet printer Labs (see issue 138, p114), not all inkjets are equally efficient, and - thanks to maintenance and cleaning procedures that use ink as the cleaning agent - there's a surprisingly large disparity in terms of how much ink in a cartridge ends up on the page. According to our tests, only half of the ink used in an Epson R240 actually ended up on the page, while printers from Lexmark and HP were much more efficient, with more than 95% of the ink being used. HP has been pushing its Vivera cartridge technology for exactly this reason.

Similar discrepancies occur with laser toner cartridges. While manufacturers declare a yield (the amount of ink used against ink wasted when printing a sheet of paper), this is based on the ISO 19752 standard, which uses a simple text document. In mixed text and graphics pages, actual yields can vary dramatically. This might not determine your next printer purchase, but it's worth thinking about, not least because it will also have an effect on running costs over the printer's lifetime.

Obviously, recycling cartridges is wise, although how you do this will depend on the printer's manufacturer. HP scores highly here, including postage-paid labels or envelopes with particular models of inkjet cartridge or laser toner, and enabling you to download postage-paid shipping labels for the rest from its website. Lexmark offers a similar service for its inkjet and toner cartridges, while Brother, Samsung and Xerox have free postage label download systems. Canon and Epson, however, will take laser toner cartridges but not inkjet cartridges. According to an Epson spokesman, this is because their cartridges don't incorporate a print head, and the plastics used have minimal environmental impact. If this still worries you, third-party ink vendors will be happy to refill them (although Epson doesn't recommend the practice).

Other third-party companies and organisations will also be happy to recycle your used inkjet and toner cartridges. If you need a little extra incentive to think green, The Recycling Factory (www.therecyclingfactory.com) will pay to recycle inkjet cartridges from HP, Lexmark and Dell (plus a limited number from Canon and Epson) along with toner cartridges from Dell, Brother, Canon, Epson, Ricoh, Samsung, Sharp and HP. You'll receive between 25p and £4 per cartridge. However, if you're feeling altruistic, other organisations will take those cartridges off your hands and use the proceeds for charity. The Printer Cartridge Recycling Scheme (www.cartridge-recycling.org.uk) recycles printer cartridges in support of children's charities, while Oxfam (www.oxfam.org.uk) has a similar programme supporting the charity's work in the third world.

Printer paper

Needless to say, the less paper your business or household uses the better, so the first step in managing this consumable is to make as much use of digital communications as possible. However, there are times when only the printed word will do. If so, recycled paper is better than regular paper and it isn't horrendously expensive. Xerox Recycled Extreme paper, for example, is available from Staples at £5.99 a ream, making it only marginally more costly than Staples' own brand laser paper (£5.49 per ream).

Another idea would be to replace ageing mono lasers with newer duplex models. Printing on both sides, you're only using half the paper per document, and if you're merely printing notes, drafts or an informal report there's little reason to do otherwise. With duplex printers suitable for personal or small workgroup use coming in at less than £200, such as the Kyocera Mita FS-1030D or the Brother HL-5250DN, there's no excuse.

In the future, reusable paper could even be an option. Toshiba's B-SX8R printer combines thermal imaging technology with a special plastic-coated media to write, erase and rewrite on the same sheet up to 500 times. At the moment, there are issues with quality (a shadow of the previous print is still visible after reprinting) and practicality (print left in daylight will permanently mark the paper). What's more, the technology is expensive, with the printer itself expected to cost £5,000, while an additional paper-washing machine (£3,000) is needed to clean the media, as it accumulates grease and dirt.

Batteries and media

If you're still using ordinary alkaline batteries for power, switch to rechargeables. A NiMH rechargeable battery can be used hundreds of times, and even if it doesn't always offer the longevity of an equivalent alkaline its reuse makes both economic and environmental sense. Even if a single NiMH battery lasted half as long as an alkaline battery and managed only 300 charging cycles, it would still save 150 batteries from going into landfill. As most will run through up to 1,000 cycles and it costs less than a penny to charge four, the argument is even more persuasive. Note that if you still use the old and toxic Nickel Cadmium rechargeables, you should replace them with NiMH cells, but note that they shouldn't be disposed of in household waste.

Finally, think more carefully about how you use and dispose of optical media - as CD-Rs and DVD-Rs have become more affordable, many individuals and companies are becoming reckless in the way they use and dispose of the discs. Use multisession burning or rewritable discs to use the same media as many times as possible and, when you're finished with a disc, don't just bin it, recycle it; the materials used in CDs and DVDs are tough and may hang around for years if sent to landfill. Various companies and organisations now offer a recycling service, and a few are listed later on in this article.