????美國環境組織塞拉俱樂部（Sierra Club）執行董事和殼牌（Shell）公司高管之間能夠達成什么樣的共識？答案是，天然氣可以作為美國的一種過渡性燃料，逐步讓美國從依賴石油轉變為廣泛使用可再生能源。

????現在爭論的重點是，這個過渡期將會持續多久。

????本周二，對水力壓裂技術持不同意見的雙方齊聚加利福尼亞舉辦的《財富》綠色頭腦風暴（Fortune's Brainstorm Green）大會，共同探討美國天然氣能源的未來。

????聯邦能源管委會（the Federal Energy Regulatory Commission）前任主席、目前擔任Wood3能源公司負責人的帕特?伍德表示，美國在理想情況下最終將轉向包括核能、太陽能和風能在內的清潔能源。他說：“那一天到來之前，上天恩賜給了我們一份大禮，那就是水力壓裂技術。”

????水力壓裂是開采天然氣時采用的一種油氣井增產技術。石油和天然氣公司從上世紀五十年代就開始在垂直井中采用這種技術。然而2003年哈里伯頓公司（Halliburton）開始在水平井采用這種方法，結果開采量大大超乎預想。

????簡單點來說，水力壓裂技術能夠讓天然氣井附近的頁巖層產生裂縫，接著向巖石裂縫注入混合著砂質的水，將天然氣擠壓出來，進入氣井。

????水力壓裂和天然氣鉆探已經在全美引發了爭議。一些美國人，尤其是那些住在東北部馬塞勒斯頁巖氣田附近的人聲稱水力壓裂已經對他們的水源造成了污染，最起碼影響到了他們的生活質量。馬塞勒斯頁巖氣田所處的兩個州，也就是紐約州和新澤西州，已經暫時禁用水力壓裂技術。

????殼牌美洲上游業務部陸上天然氣業務副總裁拉斯?福德稱：“真正的問題在于，如何妥善建設天然氣井。”他說，所謂的水壓壓裂技術帶來的污染大部分都是由于一些公司沒有正確地使用天然氣井。他說，如果天然氣井建設合理（一般來說確實如此），水力壓裂技術是安全的。

????他說，實際上，天然氣足夠安全，有能力在未來的美國能源結構中占據更大的比重。他很樂意用天然氣來替代污染嚴重的燃煤。

????但塞拉俱樂部執行董事麥克?布魯尼稱，這可能依然解決不了美國非清潔燃料的問題。塞拉俱樂部的長期目標是到2030年讓美國三分之一的燃煤發電廠停止運營。布魯尼表示，這段時間內，理想狀態下，天然氣產量如果沒有輕微下滑的話將會保持穩定，直到人們掌握了更多的信息，進一步名曲天然氣開發的安全性，以及天然氣到底是否真正屬于綠色燃料。

????但如果你詢問天然氣業內人士，你會發現，努力使天然氣成為全球主要燃料來源的系統已開始運轉。而根據伍德和其他人的觀點，水力壓裂技術是保證該系統狀態良好、運轉順利的關鍵所在。

????譯者：李玫曉/汪皓

????What can the executive director of the Sierra Club and a Shell executive agree on? That natural gas can serve as a bridge fuel in the United States, carrying the country from its dependence on oil to a widespread use of renewables.

????The main point of contention is the length of that bridge.

????Panelists on both sides of the fracking divide gathered Tuesday at Fortune's Brainstorm Green conference in California to discuss the future of natural gas in the U.S.

????Ultimately, the country will ideally transition to clean fuels including nuclear energy, solar and wind power, says Pat Wood, former chairman of the Federal Energy Regulatory Commission and currently a principal at Wood3 Resources. "Between now and then, God gave us a great big gift here with fracking."

????Fracking is a well-stimulation method used when drilling for natural gas. Oil and gas companies have used the method on vertical wells since the 1950s. But in 2003, Halliburton (HAL) started fracking along horizontal wells, allowing companies to extract much more natural gas than previously conceived.

????In simple terms, fracking creates fissures in the shale rock alongside a well, then floods those fissures with a mixture of sand and water to push gas out of the cracks and up the well.

????Fracking and gas drilling have caused controversy across the country. Some Americans, especially those living near the Marcellus Shale in the northeast, have claimed that fracking has poisoned their water, or, at the very least, their quality of life. Two states that touch the Marcellus – New York and New Jersey – have temporarily banned fracking.

????"The real issue is how you properly construct a well," says Russ Ford, the vice president of onshore gas, upstream Americas for Shell's exploration and production arm. Most of the pollution problems attributed to fracking happen when companies don't line their wells properly, he says. Ford claims that when wells are properly built, as they usually are, fracking is safe.

????Safe enough, in fact, to become an even greater portion of the U.S. energy portfolio going forward. Ford would be happy, he says, to displace dirty coal with natural gas.

????That may not solve America's unhygienic fuel problem, says Mike Brune, the executive director of the Sierra Club. The Sierra Club's long-term goal is to retire one-third of U.S. coal plants used for power generation by 2030. Over that period of time, Brune says, natural gas production will ideally remain stable if not decline slightly until more information is available on the safety of natural gas drilling, and whether natural gas is truly a green fuel.

????But if you ask the industry, the wheels making natural gas a major global fuel source are already in motion. And fracking, according to Wood and others, is the blessing keeping those wheels good and greased.