Carbon footprinting--a topic that I didn't know much about until a few months ago--is getting some serious mainstream attention. Everyone wants to know: just how many greenhouse gas emissions are generated in order to make the products we consume?

Take Apple for example. Want to know how many kilograms of greenhouse gases are emitted from your iPod nano? Check out the environmental performance report that the company posted last month. The MacBook Air itself might weigh less than 2 kg, but by the time it ends up in the recycling depot, 340 kg of greenhouse gases will have been emitted in order to make it, ship it, use it, and discard it.

Apple's not the only one who's started following their carbon footprints. The UK's Carbon Trust would like companies to start labeling products to reveal the footprint of different goods and services. Think of it as a nutritional fact label for the environment.

What else can you learn from carbon footprints? Quite a lot, according to the Wall Street Journal. Tesco learned the recipe for a low-carbon load of laundry (liquid detergent, cold water, and don't touch the clothes dryer); Patagonia found that its largest footprint was the polyester in its jackets; and Aurora Organic Dairy discovered that cows are gassy, gassy beasts.

Following carbon footprints can also help you figure out how to be a low-carbon consumer. For instance, around 70% of the carbon emitted over the life-cycle of a Toyota Prius comes from the fuel used to move it. That means that driving less frequently, more efficiently, or buying a smaller car with even better mileage can make a big difference.

But if you are thinking of trading in your old computer, think again. Since most of a computer's emissions are from the manufacturing of semiconductors, it's best to get as much life out of your PC as possible before retirement. Of course, if you can power it with renewable electricity, all the better.