Think you can’t do something about global warming? In fact, you can. Putting your PC into sleep mode when you’re not using it, such as is the default in Windows Vista after it’s idle a set amount of time, can reduce your carbon dioxide emissions by more than half a ton annually, according to Microsoft.

Microsoft’s white paper on energy conservation using Windows Vista touts that fact among others. It also adds that you’ll save $70 per year by putting your PC to sleep rather than keeping it running normally.

That figure is for a typical PC with a CRT monitor. If you use an LCD, you’ll save a little less, an estimated $56. And you’ll reduce carbon emissions less as well.

Those numbers can add up quickly. If you’ve got multiple PCs at home, for example, you can save up to several hundred dollars a year, and reduce carbon dioxide emissions by several tons. For corporations, the savings can be far more substantial.

By default, Windows Vista PCs go into sleep mode after a set amount of time. So don’t be tempted to change that and keep them running all the time — it’s best to save yourself some money, while helping save the planet.