So you're ready to make a purchase. Should you head across town and buy local? Or does it make better environmental sense to surf over to your favorite online shopping site and spend your money there?

The answer isn't always simple. But a new study conducted by Carnegie Mellon University's Green Design Institute suggests that purchases made from home may result in 35 percent less energy consumption and carbon dioxide emissions than traditional shopping. The research used data supplied by Buy.com, a Green Design Institute partner which has been developing more efficient ways to package and deliver online goods.

Researchers found that the greatest areas of impact for local shopping were from shoppers driving to and from retail locations. With online shopping, the greatest amounts of energy use and carbon dioxide emissions resulted from packaging and "last mile" customer delivery. But there was a hidden area of impact with traditional bricks-and-mortar retail: most goods sold in local stores pass through one or more tiers of regional distribution centers and warehouses before getting to the customer. Online merchants which streamline this process are able to substantially reduce its environmental footprint.

The full study, "Life Cycle Comparison of Traditional Retail and E-Commerce Logistics for Electronic Products: A Case Study of Buy.com," can be read here. (1.4 MB PDF download)

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