知识阅读 Ice That Burns
Ice that burns？ Yes， there is such a thing. It is called methane hydrate. And there is enough of it to meet our energy needs for years. But scientists have yet to figure out how to mine it without causing an environmental disaster.
Bacteria in the sediments on the ocean floor consume organic material and generate methane gas. Under high pressure and low temperature conditions ，methane forms methane hydrate， which consists of single molecules of the natural gas trapped within crystalline cages formed by frozen water molecules. A lump of methane hydrate looks like a gray ice cube. But if one puts a lighted match to it， it will burn.
Oil companies have known about methane hydrate since the 1930s， when they began using high-pressure pipelines to transport natural gas in cold climates. Unless water is carefully removed before the gas enters the pipeline， chunks of methane hydrate will impede the flow of gas.
The total reserve of the methane hydrate in the world’s oceans is estimated to be 1013 tons of carbon content，about twice the amount of carbon in all the coal， oil， and natural gas on land. However， harvesting the energy stored in methane presents a tremendous engineering challenge. It is believed that methane hydrate acts as a kind of cement to keep the ocean floor sediments together. Tampering with the hydrate deposits could cause underwater landslides， leading to the discharge of methane into the atmosphere. This event could have serious consequences for the environment， because methane is a potent greenhouse gas. In fact， scientists have speculated that the abrupt release of methane hydrates may have hastened the end of the last ice age about 10000 years age. As the great blanket of the last ice age ice melted， global sea levels swelled by more than 90 m， submerging Arctic regions rich in hydrate deposits. The relatively warm ocean water would have melted the hydrates. Unleashing tremendous amounts of methane，which led to global warming.