清洁能源来之不易

　　If all the world's theoretically recoverable shale gas could be developed, our supply of clean-burning natural gas would expand 47 percent—lowering both greenhouse gas emissions and energy prices.

　　Bloomberg Businessweek says the hitch is that the process for extracting shale gas, called hydraulic fracking, sucks up as much as 25 million liters of water for each well.

　　A report from the Washington-based World Resources Institute shows that roughly 38 percent of the world's shale gas and oil lies buried beneath water-stressed regions. This means that extraction efforts will be difficult and expensive, as well as economically and environmentally risky.

　　The situation is especially true in China.