Emissions trading has quickly gone from being a concept little known in Hong Kong to one that features in seemingly every debate about the environment. Yet although the term has taken root, most people still understand little about trading a commodity that they can neither see nor touch. Now, as we report today on Page A20, a dearth of information about a proposed emissions trading scheme between Hong Kong and the Pearl River Delta is fuelling scepticism about whether the idea would work here. The reservations are understandable. Officials have spoken about emissions trading from time to time over the past five years. But hardly any consultation papers or documents about the highly technical subject have been released. Secretary for Environment, Transport and Works Sarah Liao Sau-tung has been the government's prime advocate of emissions trading since she took up her job in 2002. In a motion debate on the subject in November that year, she disclosed that a taskforce comprising officials from Guangdong and Hong Kong would study the conditions required for emissions trading. That led to the setting up of 16 air-monitoring stations in the region in November last year under the PRD Regional Air Quality Management Plan. In August, after his annual meeting with the Guangdong governor, Chief Executive Donald Tsang Yam-kuen announced that an implementation framework for a pilot emissions trading scheme between power plants in the region had been worked out. The government is now discussing with our two power companies the identification of trading partners and emissions trading agreements. So much has been done by the government in laying the groundwork for an emissions trading scheme that the lack of details about precisely how it is to work is all the more frustrating. Perhaps a misguided desire to respect Guangdong's secretive work culture is to blame. Or perhaps the government does not want to disclose its hand in negotiating with the power companies. Whatever the reason, the lack of a proper consultation on such a major undertaking has barred interested parties from contributing to the deliberations. That has left the government in a precarious situation. Its failure to explain and consult might prompt a backlash when details of the scheme are finally released. Hopefully, this will not be the outcome. But even ardent supporters of emissions trading cannot but be amazed at what is already known about the proposed scheme. Why is it covering only sulfur dioxide, nitrogen dioxide and particulate matters, but not carbon dioxide, the leading cause of global warming? Why is the scheme targeting just power stations, when harmful discharges are also emitted by other polluters? And how will the emission caps be determined? How will the participating polluters' levels of emissions be monitored and how will violations be penalised? Perhaps the most critical issue will be the scheme's impact on electricity bills. A strong argument for emissions trading between Hong Kong and Guangdong is the big cost differentials between the two places. In theory, such differences provide the incentives for participating parties to trade. At the end of the day, however, electricity users in Hong Kong would wonder why they should 'subsidise' Guangdong power companies to clean up their air, if the terms of trade had an adverse impact on their bills. A strong community consensus exists on the need to combat regional pollution. Clean air is a major health and economic issue. The community is prepared to accept any sensible method to reduce air pollution. But before a judgment can be made, some transparency is needed. Details should be released without delay for consultation. Then, people will be able to assess whether the trading scheme worked out between Hong Kong and Guangdong officials behind closed doors is feasible. The government should resist any temptation to present a fait accompli to a sceptical public.