STEPHANIE SY:

So this is a hot spot.

Wal-Mart's mission has grown to not only reduce its own stores' impact on climate change, but to compel its tens of thousands of suppliers to transform their practices.

At Wal-Mart's urging, EDF helped pork producer Smithfield to optimize fertilizer use on crops used to feed its pigs, reducing the amount of the greenhouse gas nitrous oxide released into the atmosphere.

The reductions by Smithfield and other suppliers contributed to Wal-Mart taking credit for meeting a goal, in 2015, of reducing emissions by 20 million metric tons, the equivalent of taking nearly four million cars off the road for a year.

Wal-Mart's newest initiative is called "Project Gigaton," which aims to persuade suppliers to remove 50 times more greenhouse gases — or one billion metric tons — by 2030, about the same amount of pollution as Germany emits in a year.

Wal-Mart, known for squeezing suppliers to keep prices low, is putting a green squeeze on them now, though one that's voluntary.