Root cellars used to be part of every home. They are a good way to use the natural ground temperature to store fruits and vegetables. You can bury your cellar two feet underground to take advantage of the earth's cool temperatures. Root cellars also need humidity and air circulation so your produce doesn't spoil.
Root cellars used to be built into hillsides or mounds. They were essentially a walk-in natural freezer. I like the garbage can root cellar. It's a simple way to store enough vegetables to get you through a season.
If you dig a square hole, you can use pallets for circulation and stability. You could also recycle an old refrigerator into a root cellar, provided you give it some good ventilation. There are plenty of old materials and ways to make a root cellar. Check out Earth House for inspiration. Ehow also breaks it down nicely in 8 steps, using an old fridge or freezer.
One way to reduce your impact on the planet is to follow the 100 mile diet, eating foods within 100 miles of your home. The most difficult part of this would probably be the seasonality of fruits and vegetables. A root cellar is a great way to have local vegetables year-round. Another use of root cellars is for disaster prevention. In the event of a disaster, a root cellar and a well-stocked pantry could provide months of food.
Links: This site has a good explanation of root cellars. Here's a little of the history and usage of root cellars. Some approximate storage times can be found at the bottom of this page.
(Thanks to billygoat for the topic suggestion. I hope this helps.)