Methane hydrate is methane that is trapped in seabeds and permafrost in a crystalline structure similar to ice. This form of methane, a type of "clathrate," like all forms of methane is a hydrocarbon with potential as an energy source, but also as a greenhouse gas that can enter the atmosphere as the frozen structure melts. As permafrost thaws or seabeds warm, the methane release works as a positive feedback in anthropogenic climate change, with the potential to accelerate global warming.
As an energy source, little is known about the methods of mining methane clathrates and, therefore, the potential to contribute fugitive emissions to the atmosphere. Japan has completed a successful test to extract methane hydrates off its coast, but nothing is yet known about the environmental impacts.
(CC Image courtesy of NASA Earth Observatory on Flickr)