The Observer reports that at a meeting this week in Paris scientists will present evidence that when hydroelectric power plants are built in the tropics, the dead organic matter that accumulates in the reservoir behind the dam eventually decays releasing very large amounts of the greenhouse gases carbon dioxide and methane. As I mentioned in a post last month, I first heard about this extraordinary claim while listening to the radio show EcoTalk. It is tough enough to limit global warming without finding out that what is probably the most important clean method of generating electricity isn’t really clean. According to the Observer, not all scientists in this field agree that the emission of vast amounts of greenhouse gases occurs from hydro plants in tropical regions as some say that after a few years only modest amounts of emissions occur. Certainly global warming policy makers will need to know very soon who is right.