A woman shops in a Wal-Mart store in Pompano Beach, Florida. Wal-Mart stores, Inc. announced recently that it would wringing the carbon pollution out of its supply chain, but commentator Brad Plumber wonders if that will be enough to offset damage the company has done globally.

Wal-Mart's enormous leverage over its suppliers has attracted plenty of attention in recent years. Usually, critics home in on the negative impacts. The retailer can dictate prices to factories around the world (after all, a single producer needs Wal-Mart more than vice versa), which encourages ruthless cost-cutting that, in turn, can lead to lower wages and shoddier working conditions. And that's not even the half of it. Barry Lynn wrote a long piece for Harper's in 2006 exploring the pros and cons of Wal-Mart's vast "monopsony" power.

But there's a flip side, too. If Wal-Mart decides, say, to start wringing the carbon pollution out of its supply chain, everyone perks up. So it's a fairly big deal that, Thursday, the company announced plans to reduce 20 million tons of greenhouse-gas emissions from its suppliers by 2015. That's equal to taking 3.8 million cars off the road for a year—not a bad start. The effort, developed in partnership with Environmental Defense Fund, will focus on those products that cause the most total carbon pollution, and the cuts will be verified by an outside firm to make sure these aren't actions that would've happened anyway. (In recent months, Wal-Mart's suppliers have had to fill out surveys disclosing the full environmental costs of their products.)  Photo by Joe Raedle/Getty Images.