What journalists and even environmentalists so often fail to do in reporting on Wal-Mart’s sustainability announcements is to provide some context.

Context is everything. Consider Wal-Mart’s latest announcement: It will push some of the factories that supply its stores to cut their greenhouse gas emissions. That’s a good thing in and of itself, but what happens when we measure it against Wal-Mart’s overall impact on the production of goods?

One of the significant consequences of Wal-Mart’s rise and radical reshaping of the global economy has been a steep decline in the life span of many products. We wear out clothing, toasters, DVD players, and even furniture at a pretty rapid clip these days. It’s part of the reason Americans are now creating twice as much trash as we did twenty years ago.

Faced with relentless pressure to lower costs in order to keep their wares on big-box shelves, producers have cut corners. Even storied brands like Levi’s, once synonymous with durability, have been brought to their knees by Wal-Mart and forced to redesign their products to be cheap and short-lived.

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So, on the one hand, you have Wal-Mart’s sustainability program, which proposes to reduce the emissions associated with some of the products its sells. And, on the other hand, you have Wal-Mart’s core business model, which ensures that we have to replace those products far more often.

This is where some of our most prominent environmental groups have really failed us. They’ve loudly cheered Wal-Mart’s every green announcement, but have done little to help us understand or prod the company to confront the deep sustainability issues that are at the heart of its business model.

Wal-Mart has carefully defined the parameters of sustainability to avoid running up against the basic formula of how it operates and grows. Glaringly absent from Wal-Mart’s recent sustainability report, for example, is any mention of sprawl or land use. There’s no discussion of how much undeveloped, carbon-absorbing habitat its big stores consume each year, even as the nation’s supply of both developed retail space and abandoned “greyfields” mushrooms to epic proportions.

Nor is there any mention of how the big-box format that Wal-Mart pioneered has led to a sharp increase in the number of miles Americans drive for shopping. Although suburbanization accounts for some of this increase, most of it is a function of the basic geography of bigger stores. Each supercenter serves a larger area than the dozens of smaller grocers and other stores it replaces. This means picking up milk is a longer trip than it once was and federal data show that “one-stop-shopping” hasn’t come anywhere close to making up the difference. Indeed, since Wal-Mart began expanding in the 1970s, the number of miles logged per household for shopping has grown more than 300 percent, while household driving overall has expanded 75 percent.

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Some say that none of this really matters, because Wal-Mart is already a behemoth on the landscape and it’s better to have it be somewhat less polluting. But this is to ignore how much Wal-Mart intends to grow and how, in many cases, this growth will be replacing more sustainable economic systems with a less sustainable model. Even during a severe global recession, Wal-Mart is opening about 750 new stores a year, including about 3 supercenters per week in the U.S. and another 600 stores annually around the globe.

While it’s often suggested that Wal-Mart’s main motivation for its sustainability initiatives is to cut costs, by far the bigger financial payoff lies in preserving the company’s rapid expansion.

Just a few years ago, Wal-Mart’s ability to grow both here and abroad was in serious jeopardy. Opinion polls found sizeable numbers of shoppers were determined to find alternatives, while reports issued by stock analysts showed its growth rate was plummeting as more projects ran into roadblocks of local opposition.

Since developing a greener image, Wal-Mart has had a much easier time countering local opposition and winning over city officials.

It’s now working double-time to bring its inherently auto-oriented form of shopping to the rest of the world. One can only wonder at the staggering carbon impact of that transformation.

But where I find the lack of broader context and analysis most troubling of all is in the way some environmentalists have gleefully embraced Wal-Mart’s sheer power. It is true that small changes can add up to big numbers at Wal-Mart’s scale. But if we step back for a moment and ask ourselves why, despite popular support and compelling scientific evidence, we have been unable to address legislatively the biggest environmental challenges of our day, one has to finger concentrated power as a culprit. Large corporate interests have hijacked our government and we have failed to act as citizens to take it back.

Concentrated economic power is a threat to democracy, not only because it invariably translates into political power, but also because Wal-Mart and all the giants it is interconnected with, from Monsanto to Goldman Sachs, have rendered ours an ever less entrepreneurial society. Few Americans can lay claim to any measure of economic autonomy today. We are increasingly powerless employees and passive consumers. Having acquiesced to the Wal-Mart-run economy, where the most important decision we’re allowed to make is paper or plastic, it’s no wonder that we as a society seem unable to marshal the full power of our citizenship.