Methane hydrate. Computer model of the structure of methane hydrate, also known as methane ice or methane clathrate. It consists of a molecule of methane, which is composed of carbon (green) and hydrogen (white), surrounded by a cage of water molecules, which are composed of oxygen (blue) and hydrogen. The water molecules are joined by hydrogen bonds (dotted lines). This whole structure is known as a clathrate. Methane hydrate is found in the very cold and high pressure environments under the arctic permafrost and in marine sediments, where it forms a crystalline solid. It is thought there is approximately 3000 times the volume of methane in hydrates than in the atmosphere, making it a huge potential energy source. However, methane is a greenhouse gas and so any release would contribute towards global warming.