I've got a few quibbles with the way the following is framed (does 'urban resident' automatically mean 'middle class') and I think the piece tends to underplay the way in which pollution has always been a major factor in rural mass incidents, often linked to land seizures for development pruposes, but this is a fascinating article on the dynamics of 'environment' as an issue in protest in China's urban space - never exactly a pretext, but often not the whole story either:
Environmental protection officials and some researchers delight in pointing out that the main causes of these cases of unrest are not actually environmental problems. For example, the proposed smelting plant which sparked protests in Shifang would actually have reduced pollution by replacing smaller and less advanced firms. But the bosses of those smaller firms, unhappy with their lot, encouraged the public to protest. In Ningbo the villagers were unhappy with levels of compensation for relocation, and used the “environmental” banner to bring urban residents out onto the streets.
There is some truth to these views. Unrest is caused by conflict of interests, and conflicts of interests are not just confined to the environment. Environmental issues may just be a politically safe excuse for protest, and the Ministry of Environmental Protection cannot step in and make up for local government failings.
...Although the environmental authorities do not have much power, they represent the central government stance on environmental matters. When the people and the government clash, local government tends to treat those defending their rights as unruly troublemakers to be supressed. But the environmental authorities, representing central government, cannot be ignored, and so conflict is avoided. The prompt appearance of the environmental authorities also maintains the authority and credibility of central government.
Liu Jianqiang notes that protests have become more frequent over the past five years as the Environmental Protection Ministry has become much less active in policing development projects. It may be that this in turn was part of China's internal stimulus in response to the global financial crisis. China would hardly be the only place where the whole green package has just fallen off the agenda.