This week, an estimated 100,000 people will take part in the People’s Climate March, a national effort to somehow, someway persuade the U.S. government to take action on the most pressing environmental crisis of our time.

But after the march, they should head to Wal-Mart.

Why? Because contrary to popular perception, the retail behemoth—the largest employer in 19 states, with $482 billion in annual revenue—is leading the way on corporate climate action. Last week, it announced a commitment to eliminate a gigaton—that’s 1 billion tons—of greenhouse-gas emissions from its supply chain. Yup, Wal-Mart.

“There’s good news here,” said Elizabeth Sturcken, managing director of the EDF+Business program at the Environmental Defense Fund, in an interview with The Daily Beast. Wal-Mart’s proposed cut is more than the annual greenhouse-gas emissions of Germany, Sturcken noted.

Corporate environmentalism is not new, and the EDF in particular has a long history of working with companies to lessen their environmental footprint. Famously or infamously, depending on your point of view, it partnered with McDonald’s in 1990 to eliminate its wasteful “clamshell” packaging and replace it with environmentally friendly alternatives.

Of course, to some, the EDF’s work with McDonald’s and Wal-Mart is a form of “greenwashing,” which is when companies merely rearrange the deck chairs on their environmental Titanic, and then get a PR boost. Indeed, when EDF announced its Golden Arches work 27 years ago, the then-head of Greenpeace said that if the fast-food giant really wanted to help the environment, it would shut its doors.

On the other hand, corporations like Wal-Mart are leading where the U.S. government fears to tread.

With the Republican Party in the pocket of the fossil-fuel industry, the federal government is wedded to a head-in-the-ground denial of the universal consensus of climate scientists that the world is getting hotter and that human activities’ emissions of greenhouse gases are the reason why. Thus, while there is some progress on the state and local level, national action, and by extension the international action that requires U.S. participation, is headed in the wrong direction.

Of course, multinationals like Wal-Mart also have to comply with other countries’ environmental regulations, but in general, Sturcken said, “Companies aren’t waiting for government action. Companies are driven by data, by science. Truth matters. And the only conclusion you can come to, if your company is looking toward the horizon and you want your business to grow… is to be pro-active on these issues.”

Because Wal-Mart is so large, the effects are staggering. According to Sturcken, the retail giant has more than 100,000 global suppliers, and more than 230 million people shop at Wal-Mart every week. “We’ve been working with Wal-Mart for 10 years because of their power to create change,” she said.

In 2010, for example, Wal-Mart agreed to cut 20 million metric tons of annual emissions in the products it sells, Sturcken says, by taking thousands of small actions like “selling low-flow shower heads, changing date labeling on food products to be use-by instead of sell-by, selling more efficient light bulbs, and asking food suppliers to optimize fertilizer use.” The goal was exceeded in 2015.

That kind of change is possible because of Wal-Mart’s outsize influence on its suppliers. No one business could have such a large impact, but a business that influences thousands of others can. “Companies are saying that the challenges and opportunities go beyond their four walls to consumers they touch and products they sell,” Sturcken said.

The publicity benefit of such steps is obvious, which is why oil companies run pro-environment ads in newspapers and on cable news while fighting climate-change regulations in Washington. But Sturcken said the real business value lies elsewhere. “There is immense business value creation in sustainability,” said Sturcken. “That goes back to our partnership with FedEx in the late 1990s to create next-generation trucks: The company saw that it was smart business to get ahead of these issues and be a leader.”

According to Sturcken, this is true even of relatively conservative companies. For example, Smithfield, the pork producer, committed to reduce its GHG emissions 25 percent by 2025. Land O’Lakes has created a business unit focused on sustainability. “These are conservative companies but they’re reality-based and smart,” said Sturcken. “If they’re thinking ahead, they’re thinking of opportunities and seeing customers demand good corporate citizenship.”

OK, but really—Wal-Mart? Aren’t they the ones wrecking local retail economies, treating workers poorly, and hiding money in tax havens?

Sturcken was insistent. “I would say that Wal-Mart is the leading retail company on sustainability. And the reason why I say that is the scale… They’ve made significant strides.

“In terms of volume, they’re the leading organic retailer,” Sturcken said. (Costco claims the same thing.) “The place you see the real impact, is that sustainability is baked into everyday products that consumers who are middle-class can afford… I really do believe they’re not getting enough credit for the change they’re creating here.”

As for its own emissions, “Wal-Mart has a GHG-reduction target for their own operations of 18 percent by 2025. They’re working on factory energy efficiency with Chinese factories… They’re far from sustainable, but let’s praise leadership and not knock down companies because they’re not perfect yet.”

Sturcken emphasized that “EDF does not take money from any of our corporate partners… It’s risky for us to partner with a company and risky for them to partner with us, and it’s better for us to maintain independence and credibility by not taking money.”

I asked Sturcken if she had any advice for the people marching this weekend. Her response was surprising. “Making your individual voice heard does make a difference,” she said. “Not just signing a petition but picking up the phone and placing a call to the CEO of a company that needs to step up will make a huge difference. If everyone from the Climate March did something like that, it would be extremely powerful. Those kinds of things get through the noise to resonate with companies’ boards and executives.”

Of course, such actions will still not be enough. “The planetary imperative is that we need change faster and at scale,” Sturcken said. “You still need policy change. Voluntary corporate action is leading the way right now in this time when the government is going backward, but it’s not enough. We absolutely need policy to deal with issues that are global like climate change. There’s no other way.”