Walmart, among the world's largest retail chains, has set a goal of eliminating 20 million metric tons of greenhouse gas emission from its global supply chain by 2015.

The amount is 1.5 times the company's estimated global carbon footprint growth over the next five years and is the equivalent of taking more than 3.8 million cars off the road for a year. The goal is to remove the emissions from the the supply chain with the cooperation of suppliers, manufacturers, transportation companies and others, rather than just from the operational carbon footprint of the stores themselves.

"We've been working to make a difference in these areas, both in our own footprint and our supply chain," says Mike Duke, Walmart president. The firm feels the supply chain reductions will spread the impact."

Walmart is working with the Environmental Defense Fund and the Applied Sustainability Center at the University of Arkansas and others in implementing and measuring the reductions. The effort will focus on the the most popular products the company sells that create the most greenhouse gas emissions.

Changes will be made in the raw materials, manufacturing, transportation, customer use or end-of-use disposal of the product. ClearCarbon and PricewaterhouseCoopers will assess the results.