China's central government has repeatedly declared its intention to clean up the environment, from the smoggy skies of Beijing to the scummy green waters of Lake Tai in the Yangtze delta. However, ensuring that intentions are translated promptly, fairly and efficiently into action across the provinces is often a problem.

Two non-governmental organizations (NGOs) may be about to change this. On 3 June, the Institute of Public and Environmental Affairs (IPE) in Beijing and the Natural Resources Defense Council in New York posted their first Pollution Information Transparency Index on the Internet. The index ranks 113 Chinese cities on how well they informed the public about pollution-related legal violations in 2008 — specifically, by measuring their adherence to the national environment-information disclosure measures that came into effect on 1 May, 2008. The index incorporates data on how complete the cities' disclosures are, whether they are timely, what measures have been taken in response and whether the disclosures are user-friendly. The potential maximum score is 100. However, the average score for 2008 was only 30, and just four cities scored more than 60.

The two NGOs hope that the ranking will pressure local governments to recognize and be more responsive to the kind of situation that developed in Yangzong Lake in southern China. From 2001 to 2008, the lake — which supplied drinking water for 26,000 people — was polluted with arsenic by a chemical company, despite fines and promises of action from local officials.

The index is also intended to make role models out of the best-performing local governments. In each of eight categories, the IPE designated a top scorer. Taken together, they form a 'dream team' that scored 89.5 points. “This shows that a high level of information disclosure is possible in China,” says Wang Jingjing at the IPE.

The system has limitations, however. It can only report on cases already recognized in official documents. That is not often an issue, says Wang, and an official source is usually available when the IPE hears of a complaint. But the group has no authority to push for further investigation if information is not available. Only 89 of 113 local environmental protection offices returned their calls.

A deeper problem is that the environmental laws themselves are not clear on crucial issues such as penalties for non-compliance. And in any case, the bar is pretty low. For example, Beijing ranks as one of the most transparent cities on the list, even though allegations that officials were manipulating data ahead of the Olympics have been met with denial, and little in terms of explanation (see Nature doi:10.1038/news.2009.578; 2009).

Although it is easy to be sceptical, local newspapers are paying attention to the index. In a face-saving society, local bureaucrats might now have to explain why they are at the bottom of the list. “The first thing to do is encourage public participation,” says Wang. “But to do that people have to know what is happening.”

The effort will also give central and local lawmakers a better idea of what is happening, and enable them to see whether laws need to be changed to ensure that China can make good on its intentions.