Perhaps the biggest unanswered question hovering over each round of international climate change talks is whether China can be trusted to abide by any carbon reduction commitments it agrees to. Given Beijing's history of pushing for vague, nonbinding targets — and its reported intervention last weekend to block efforts to include a rigorous review process in the Lima Accord — there's grounds for skepticism.

But a recent development in China gives clear reason to be optimistic. Last Tuesday, the Institute of Public & Environmental Affairs (IPE), a Beijing-based NGO, published a report on air pollution produced by publicly listed companies operating in China. At first glance, the data seems to confirm that most Chinese companies have little reason to abide by pollution laws and regulations.

The mere existence of the data, however, suggests something far more important: China, after decades of prioritizing economic growth over the environment, now seems willing to pressure and even embarrass some of its most powerful corporate citizens in order to curb pollution.