Walmart, the world's largest retailer, says it wants its suppliers to reduce 20 million metric tons of greenhouse gas emissions by the end of 2015. 

The discounter's push to eliminate what it says is the equivalent of 3.8 million cars off the road for a year goes beyond its efforts to date to reduce its own emissions by designing more energy-efficient stores and other measures.

Walmart is collaborating with the Environmental Defense Fund and other environmental experts to measure reduction. It said it won't force suppliers to make changes but will work with them on projects that will reduce both emissions and costs.

Walmart CEO and President Mike Duke said that the company needs to push for greater efficiency to maintain a competitive edge as it expands globally amid higher energy costs.

"We need to continue to build stores and add retail selling space. Yet we know we need to get ready for a world in which energy will only be more expensive and there will only be a greater need to operate with less carbon in the supply chain," Duke said.

Walmart plans to focus on product categories that have the highest carbon footprint and work with those suppliers to reduce emissions from any part of the product's life cycle. That could include sourcing the raw materials, manufacturing, transportation, the use of the product or the disposal.

The company said it will provide a team of experts to work with the suppliers to assess how they can cut emissions.

Walmart works with more than 100,000 suppliers and generated sales of more than $400 billion last year. Its massive size gives it tremendous influence among makers of all kinds of products - muscle that gives its efforts a chance for wider adoption that other retailers might not have.

Last July, Walmart unveiled a plan to develop eco-ratings for products it sells.

©2010AP