加拿大薩斯克徹溫省伊斯得芬的大草原上已建妥一座燃煤發電廠，取代曾經排放大量煤灰，讓戶外晾曬的衣物蒙上一層塵粒的舊發電廠。

But as with even the most modern coal plants, its smokestacks still emit enormous amounts of carbon dioxide, the invisible gas that is the main contributor to global warming. So this fall, a new maze of pipes and tanks will suck up 90 percent of the carbon dioxide from one of the boilers so it can be shipped out for burial, deep underground.

燃煤電廠再現代化，煙囪還是會排放大量二氧化碳。這種看不見的氣體是促成全球暖化的關鍵。新的輸送管與儲存槽今秋將自其中一個鍋爐吸取九成二氧化碳，運出並深埋地底。

The effort will be the first major one of its kind at a power plant, the equivalent of taking about 250,000 cars off the road. And at least in theory, that carbon dioxide will be kept out of the atmosphere forever.

這將是發電廠首次做此類重大嘗試，相當於減少25萬輛汽車的排放量。至少在理論上這些二氧化碳永遠不會逸入大氣層。

Worldwide, coal consumption in 2020 will be about twice what it was in 2000, according to the United States Energy Information Administration, and will continue to grow for decades.

美國能源資訊局表示，2020年全球煤消耗量預估會是2000年的兩倍，其後數十年還會繼續增加。

“If you want to carry on using those fossil hydrocarbons, that means cleaning up their emissions,” said Stuart Haszeldine of the University of Edinburgh. Capturing carbon, he said, “is the single best way of doing that.”

愛丁堡大學的哈塞爾丁說：「若要繼續使用這些化石碳氫化合物，這意味你必須清理它們的排放物。捕集碳是最好的方法。」

Yet because it requires so much energy, sucking up carbon reduces a plant’s ability to make electricity . There are basic questions of whether carbon dioxide can be safely stored underground. And the technology is expensive. Updating the Saskatchewan plant alone cost $1.2 billion .

然而捕集碳耗費大量能源，會使發電廠的發電量減低。二氧化碳能否安全儲存於地底，也還有些基本問題尚待解答，而且技術所費不貲。僅是在薩斯克徹溫興建另一座發電廠就耗資12億美元。

In the pine woods of central Mississippi, another carbon-capture effort is taking shape, in a massive new power plant that will be fed a steady diet of coal from the strip mine next door.

在密西西比州中部的松林，另一項捕集碳的嘗試正在進行。一座新建的大型發電廠所需的煤將由毗鄰的露天礦場供應。

Bruce Harrington, the operations manager, said an army of workers is cutting, welding and testing underground. The plant’s owner, Southern Company, hopes to open the structure next year. But it is more complex than the Saskatchewan effort, and the price tag is now $5.5 billion.

作業經理哈靈頓表示，工人正在地面下切割、焊接及測試。業主南方公司希望這座設施可於明年啟用。然而這項計畫比薩斯克徹溫的複雜，目前估計的成本是55億美元。

The United States and other nations have helped some projects — Canada gave $220 million to the Saskatchewan plant’s owner, SaskPower, and Southern Company received $270 million from the United States Department of Energy — but the costs are high enough that few other power companies have done much beyond study the concept.

美國與另一些國家已經贊助一些類似的方案。加拿大政府補助經營薩斯克徹溫發電廠的薩斯克電力公司2.2億美元，美國能源部則補助南方公司2.7億美元。然而由於成本太高，絕大多數電力公司僅止於研究這個構想而已。

The technology has been around for nearly a century, used at some refineries and other industrial plants, including large ones in Illinois, North Dakota, Canada and Norway.

必要的技術問世已將近一個世紀，主要用於一些煉油廠與其他工廠，包括伊利諾州、北達科他州、加拿大與挪威的一些大型工廠。

But removing carbon dioxide from the swirl of gases unleashed at a power plant is challenging. T he equipment is enormous. At the Saskatchewan plant, called Boundary Dam, a liquid chemical latches onto carbon dioxide molecules after being sprayed onto a plume of combustion gases. The “stripper,” where the carbon dioxide is finally pulled away, is nearly 50 meters high .

然而從發電廠所排放的各種氣體中取出二氧化碳卻是個挑戰。必要的設備體積龐大。在名為「邊界水壩」的薩斯克徹溫發電廠，一種液態化學劑噴向一縷燃燒氣體之後，就會與二氧化碳分子結合。最後取走二氧化碳的清除器高度將近50公尺。

In addition, efficiency is lost because some of the steam that would normally generate electricity goes to the stripper instead.

此外，效率也會折損，因為通常用於發電的蒸汽有一部分也會逸入清除器。

And a monstrous motor compresses the carbon dioxide — until it effectively becomes a liquid — for transport. All told, capturing the carbon dioxide at Boundary Dam will sap electricity generation by about 20 percent . Injecting liquids deep underground can present problems, too. Pumping wastewater from oil and gas production into the ground has been linked to small earthquakes in the United States.

一部巨大的馬達壓縮二氧化碳，直到它成為便於運送的液態。整體而言，邊界水壩捕集二氧化碳大約會使發電量減少20%。把液體注入地底深處也會產生一些問題。將開採石油、天然氣所產生的廢水注入地底經證明與美國的一些輕微地震有關。

The carbon dioxide could taint drinking water, or bubble up into the atmosphere, defeating the entire purpose.

二氧化碳可能汙染飲用水或逸出並進入大氣層，導致整個計畫完全失敗。

Still, carbon dioxide has been buried around the world with few problems. In Norway, about a million metric tons have been stored every year since 1996, injected into sandstone about 900 meters beneath the North Sea. Most of Boundary Dam’s carbon dioxide will become a tool to extract and consume oil.

實際上，二氧化碳已在全球各地掩埋，而且並未產生太多問題。在挪威，1996年起，每年約有100萬公噸的二氧化碳注入北海海底下約900公尺處的沙岩層。邊界水壩的二氧化碳大多會成為開採並消耗石油的工具。

After being sold and shipped through a 60-kilometer pipeline to an oil field, the carbon dioxide will be pumped into old wells, where it will mix with the oil inside, making it flow better. The process is known as enhanced oil recovery . The oil and gas industry has done this for decades, mostly with naturally occurring carbon dioxide that accumulates underground. But each year in North America, more than 13 million metric tons of carbon dioxide from industry are used as well.

二氧化碳賣出並經由一條60公里長的管路輸送到一處油田之後，打入舊油井，與裡面的石油混合，提高石油的流動性。這項流程名為強化採油，在石油、天然氣業已行之數十年，大多是使用在地底自然累積的二氧化碳。不過在北美地區，每年平均也會使用超過1300萬公噸工業界產生的二氧化碳。

The practice could be expanded at many oil fields , experts say, potentially storing billions of metric tons of carbon dioxide and serving as a bridge to the day when it becomes necessary, and economical, to store the gas elsewhere.

專家說，這種流程可在許多油田推廣，可能足以儲存數十億公噸的二氧化碳，同時充當有朝一日必要且具有經濟效益時，在其他地區儲存二氧化碳的銜接階段。

The prognosis for carbon capture around the world is unclear.

捕集二氧化碳的全球性前景仍不明朗。

If the United States moves forward with President Obama’s plans to cut carbon emissions, China and other countries may make bigger strides as well.

如果美國總統歐巴馬的二氧化碳減排計畫得以落實，中國大陸與其他國家也可能大步跟進。

“How this will play out over time is hard to tell,” said Edward S. Ruben of Carnegie Mellon University in Pennsylvania. “Inevitably, there will be a balance between technological capability, cost and political realities.”

賓州卡內基美隆大學的魯本說：「這件事會如何發展很難說。技術、成本與政治現實之間必將取得平衡。」

在以視野遼闊、山脈起伏與河谷高深著稱的美國亞利桑納州李斯渡口（編按；大峽谷的起點），檉柳甲蟲肆虐的痕跡隨處可見。

For stretches along the banks of the Colorado River, hundreds of tamarisk trees — also known as salt cedars — are gray and withered. Their parched branches look like victims of fire or drought.

在科羅拉多河兩岸的部分地區，數百棵又稱紅荊的的檉柳呈灰色已經枯萎。它們的樹枝已經乾枯，彷彿火災或乾旱的受害者。

But this is not the story of beloved trees being ravaged by an invasive pest . Farmers, ranchers and the water authorities here are eager to get rid of the tamarisk trees, which are not native to Arizona and which they say suck too much water.

然而這不是人們鍾愛的樹木被外來害蟲蹂躪的故事。當地的農民、牧場經營者與水資源當局急於剷除這些吸收太多水分的非本土樹種。

They have welcomed the beetles, which have made their way from Colorado and Utah over the last decade, and have watched as the centimeter-long workhorses have damaged the trees by eating their spindly leaves. The hope is that the beetles will now rid Arizona of the trees.

他們歡迎過去10年自科羅拉多州與猶他州一路而來的甲蟲，看著體長僅一公分的牠們啃食檉柳的細長葉子，使檉柳受到重創。他們希望甲蟲能夠替亞利桑納州除掉這種樹。

“We view the tamarisk as a pest,” said Joseph Sigg of the Arizona Farm Bureau.

亞利桑納州農業局的席格說：「我們把檉柳視為有害的樹種。」

But scientists say that nature is rarely a zero-sum game, and that removing the deep-rooted tamarisks — which the authorities have tried with bulldozers, chain saws and now beetles — will not produce more water. New tamarisks or other trees will replace the fallen ones, the scientists say, and the birds that live in the tamarisks, like the endangered Southwestern willow flycatcher, will be harmed.

當局曾經嘗試以推土機、電鋸與如今的甲蟲對付這些檉柳。然而科學家表示，大自然不是零和遊戲，剷除這些扎根很深的樹不會使水量增加，新的檉柳或其他樹木會取而代之，以檉柳為家的鳥類，如瀕危的西南柳樹鶲，必然受害。

Plus, once the beetles are done eating tamarisk leaves, they are likely to feed on other trees. Ruinous droughts and rapid population growth in recent years have strained the state’s vulnerable water supply and heightened the scramble to find new solutions, from desalination to cloud seeding to vegetation management, which includes eliminating the tamarisk.

還有，啃完檉柳的葉子之後，這些甲蟲可能繼續啃食其他樹木。

近年來的多次嚴重乾旱與人口快速增加導致該州原已不足的水供應更加吃緊，促使有關方面加緊尋找其他對策，包括去鹽化、人工造雨與植被管理，其中包括消除檉柳。

The tamarisk, which lives in Asia and the Middle East, was imported more than a century ago to prevent erosion. With a dense and sprawling network of roots and an ability to thrive in arid terrain, it did that job well.

當地人為了防止土壤侵蝕而於100多年前引進原產於亞洲與中東的檉柳。它們根部濃密，蔓延面積大，可在不毛之地存活，充分發揮了作用。

But as rivers were dammed, riverbanks receded, starving native trees and pushing out the insects, birds and other wildlife that relied on them. In their place, the tamarisk took over.

然而隨著河流築壩，河岸為之倒退，導致本地樹木枯死，仰賴它們的昆蟲、鳥類與其他野生動物遷至他處。檉柳取而代之。

Advocates of removing the tamarisk claim that a mature tree can consume more than 750 liters of water a day.

主張剷除檉柳的人說，一棵成熟的檉柳每天可消耗逾750公升的水。

There is little proof, though, that removing the tamarisk will increase the amount of available water. And if thirstier trees replace it, there could be even less .

不過並無具體證據足證，剷除檉柳會使可用的水增加，而如果被更會喝水的樹木取代，可用的水將更少。

While the beetle appears to be efficient at defoliating tamarisk trees, it works on its own schedule, which is why the tree is still often removed manually. It is a costly and imperfect process.

甲蟲似可有效啃掉檉柳葉，卻有自己的作息時間表。因此檉柳經常還是須以人力移除。這麼做很花錢，效果也不理想。

To save money and avoid the constant culling, the United States Department of Agriculture studied how to introduce the tamarisk beetle, the tree’s natural predator. About a decade ago, the first beetles were released in Colorado, and despite predictions that they would move slowly, they have arrived in Northern Arizona sooner than expected.

為了省錢與避免必須不斷移除，美國農業部開始研究如何引進檉柳的天敵甲蟲。大約10年前，在科羅拉多州釋放了第一批甲蟲。雖然當局預期牠們移動速度會很緩慢，牠們卻提早抵達了亞利桑納州北部地區。

The beetles are likely to reach the southern parts of Arizona in about two years, said Stacy Beaugh of the Tamarisk Coalition, which restores riversides.

檉柳聯盟專門復育河畔，成員史黛絲•畢奧格表示，這些甲蟲可能兩年後就會抵達亞利桑納州南部。

“It hasn’t been overnight, but it’s been much faster than expected,” she said.

她說：「不是一夜之間就來到，卻比預期快許多。」

On this stretch of the Colorado River near the Grand Canyon National Park, the beetles’ handiwork is evident . But the trees’ roots are so dense that it may take several seasons before they die, said Gibney Siemion, an ecologist with the Grand Canyon Wildlands Council, which spent $24,000 to remove the trees.

在鄰近大峽谷國家公園的科羅拉多河李斯渡口河段，甲蟲的工作成果明顯可見。不過大峽谷荒野協會的生態專家塞米恩表示，由於檉柳的根部實在太密，可能幾季之後才會枯死。該協會曾以2.4萬美元的經費移除檉柳。

Kelly Burke of the council said that 15 people spent 10 days cutting tamarisks from a two-hectare slice of shoreline 14 kilometers downriver from the Glen Canyon Dam. They applied Garlon, a herbicide, to the stumps, and the fallen trees were burned. Yet nearly five years later, tamarisk saplings have sprouted next to the blackened stumps, a reminder of how difficult it is to remove a tree that produces hundreds of millions of seeds.

協會的凱莉•柏克表示，協會委託15人以10天的時間，砍除葛蘭峽谷大壩下游14公里處2公頃岸線地帶的檉柳。他們對殘幹施用「賈農」除草劑，同時燃燒倒下的檉柳。然而將近五年之後，檉柳的幼樹在焦黑殘幹旁快速成長，證明要剷除可產生無數種子的檉柳何其困難。

“You’ll never get the last tree,” Ms. Siemion said . “You do your best, but the tamarisk is very adaptable.”

塞米恩說：「你永遠不可能砍到最後一棵檉柳。你盡力而為，檉柳卻有很強的適應力。」