作者 「科學美國人」(Scientific American)二月刊發表一項令我們憂喜參半的新技術，看起來相當不錯，很有可能可以減輕嚴重的環境問題，使我幾乎無法駁斥它。不過當我反覆思考之後，我開始有些懷疑了。
這項新技術被稱做碳封存(carbon sequestration)，它可以將企業所排放的二氧化碳(像是燒煤的火力發電廠)蒐集起來，然後把它埋在地底深層或是海洋中。據估計，我們的經濟體系所排放出來的溫室效應氣體當中，二氧化碳佔了三分之二，如果我們可以把它丟到任何一個不屬於大氣層的地方並保存好，那我們就可以在不會破壞氣候的情形下使用石化燃料了。
我們知道碳封存是可行的，因為在某些地方已經這樣做了。天然氣常會跟二氧化碳一起由地底衝出來，通常二氧化碳在從油井衝出來後便釋放到空氣中。但是在同時開採石油及天然氣的過程中，二氧化碳常會被重新注入油井內，以便能再抽取更多的石油，而這項應用的花費則由所增加的石油產量來支付。在美國，每年就能封存四千三百萬噸的二氧化碳，聽起來好像很多，但這數量還不到全球排放二氧化碳總量的百分之一呢。
挪威(Norway)一座海上的Sleipner油田是世界上唯一一座把二氧化碳送回地底下，但並不是為了能開採更多的油，而純粹是為了保護我們現在的氣候的油田。每年約有一百萬噸的二氧化碳被注入海床下三千英尺的砂岩層中，大約是挪威排放二氧化碳總量的百分之三。從經濟上來看這樣的行為是有道理的，因為挪威政府課徵了一項排放稅，每排放一噸的二氧化碳收取五十美元的稅金，這要比Sleipner把二氧化碳埋起來的花費便宜多了。
如果我們都跟挪威人一樣聰明的話，各地應該都要徵收二氧化碳排放稅，碳封存也將是經濟實用的，而由人類所造成的溫室效應也將減輕，我熱切盼望這樣的結果可以實現，我所擔心的是事情就這樣結束了，我們可能會鬆懈，以為我們已經找到了打破問題的神奇子彈，能讓我們繼續盡情地駕駛著耗油的運旅車(sport utility vehicles)。
但是子彈只能作用在單一目標，單一問題，單一原因，單一影響上。而在這裡，我們至少有兩個問題，能源及氣候，以及許多原因及影響。二氧化碳是最普遍的，但並非唯一會改變氣候的氣體，而氣候變化是使用石化燃料最主要，但也非唯一的影響。我們無法封存每一個來自燃燒煤、油及氣體所產生的二氧化碳分子。而就算我們能做到，我們還是有漏油、酸雨、城市煙霧、污染的地下水層，露天採礦、中東安全問題、能源耗盡及其他所有和無法再生、分布不均、濕黏的石化燃料有關的，令人頭痛的問題。
「還好」是「最好」的敵人。碳封存只是還好而已，最好的能源科技是那些只需少少的能源便能提供我們燈光、熱及行動所需的動力。省遊的車、絕緣效率高的燈泡及器具，這些改革不只減輕一項不好的影響，而是經由減低石化燃料的使用，而減輕所有負面的影響(至少有減輕90%的潛力)。
次好的能源科技是取自於能再生的能源，如太陽能、風、水力及氫，尤其是在我們能更有效率地使用能源之後。這些可再生能源雖不見得完全對環境無害，但比其他的能源要好得多。
再下一個最好的能源科技是使用天然氣，尤其是與碳封存技術結合，不需要在很深的地方進行。造林與堆肥可以將碳儲存在樹木及土壤中，這種封存方法除了可以隱藏更多的二氧化碳，同時也可以保持水分，穩定氣候，肥沃土壤，美化環境且所費不多，每個人都可以做得到。
如果我們能照著這個列表順序選用能源，我們就不需要再生產油、煤或是核能。
如果我們有任何的神奇子彈可以使用，那一定是經濟的、非科技性的，需要我們大家都能比挪威人再聰明一些。我們不只要跟油管末端的使用者徵收碳排放稅，更要向油管源頭的能源製造者徵收。這個稅要依對環境造成危害的比例來徵收，對有效率的能源使用可以免徵，使用可再生能源者則收少一些，有做好生物性碳封存(樹木及堆肥)的天然氣能源使用要多收一些，像「科學美國人」(Scientific American)期刊所描述的深層碳封存則收更多一些，沒做碳封存者還要收更多，而像是使用油、煤及核能等能源者要收最高的稅金。
這看起來像是一種稅，它也許可以用其他稅來替代，但這是一種修正市場錯誤的方法。它反應實際的成本，某個時間在某個地點就必須有人付出代價－氣候變遷、空氣污染、酸雨等的代價，這是我們使用這些能源時該付出的價錢。污染者付費。使碳封存像太陽能一樣在各地使用都很划算，而且效率更好。運旅車一加侖可以跑一百英里，或是用氫做動力或是兩者都可以達成。
一個經濟的神奇子彈，可以讓所有科技的子彈對準正確的目標。
by Donella H. Meadows 02.28.00
The February issue of Scientific American tells of a new technology that makes me both rejoice and worry. It looks so great, so likely to relieve a massive environmental problem that there's no way I could oppose it. But on second, third, and fourth thought, I have some doubts.
The technology is called carbon sequestration. It takes carbon dioxide as it is spewed out by a human enterprise (such as a coal-fired power plant) and buries it deep underground or in the ocean. Carbon dioxide accounts for two-thirds of the greenhouse gases our economy emits. If we could put it somewhere other than the atmosphere and keep it there, we could burn fossil fuel without crazing the climate.
We know carbon sequestration can work, because in some places it already does. Natural gas tends to come out of the ground mixed with carbon dioxide, which is usually stripped out at the well and released into the air. But at operations where both gas and oil are produced, the carbon dioxide is often injected back into the well, where it helps push up more oil. This practice pays for itself in enhanced oil recovery. In the United States it sequesters 43 million tons of carbon dioxide a year. That sounds like a lot, but it's less than 1 percent of global carbon dioxide emissions.
The Sleipner gas field off the shore of Norway is the only one in the world that sends carbon dioxide underground not to bring up more oil, but purely to protect the climate. About one million tons of carbon dioxide per year -- three percent of Norway's total emissions -- go into a sandstone bed 3,000 feet below the sea floor. This venture makes economic sense only because Norway imposes an emission tax of $50 per ton of carbon dioxide. It is far cheaper for Sleipner to bury the stuff than to pay that tax.
If we all were as sensible as the Norwegians, there would be a carbon tax everywhere, carbon sequestration would be economic, and the human-induced greenhouse effect would be slowed. I fervently hope that happens. What worries me is the possibility that that will be the end of the story, that we will relax, thinking we've found a magic bullet that lets us go on driving gas-guzzling SUVs to our hearts' delight.
Bullets only work when there's a single target, one problem, one neat cause, one effect. In this case we have at least two problems, energy and climate, and many causes and effects. Carbon dioxide is the most prevalent climate-changing gas, but not the only one. Climate change is a major side effect of fossil fuel burning, but not the only one. We can't begin to sequester every carbon dioxide molecule coming from burning coal, oil, and gas, but even if we could, we would still have oil spills, acid rain, urban smog, messed up aquifers, strip mines, Middle East security worries, depletion, and all the other headaches associated with nonrenewable, unevenly located, sloppy fossil fuels.
The good is the enemy of the best. Carbon sequestration is only good. The best energy technologies are those that give us light, heat, or motion using much less energy. High-mileage cars. Insulation. Efficient light bulbs and appliances. These innovations don't alleviate just one bad effect, they alleviate them all by reducing (potentially by at least 90 percent) fuel use itself.
Next best, especially after we've reduced energy use through efficiency, are technologies that tap renewable sources. Solar. Wind. Hydro. Hydrogen. Not completely benign by any means, but much more so than the options farther down the list.
Next would be natural gas, especially if combined with carbon sequestration, which does not need to take place in deep earth or deep water. Reforestation and composting store carbon in trees and soil. These forms of sequestration do more than hide carbon dioxide; they also hold water, moderate climate, provide habitat for living things, fertilize soil, look beautiful, and cost little. And can be done by anyone.
If we work our way down this list of preferences, we need never come to oil, coal, or nuclear power.
If there's any magic bullet available to us, it's economic, not technical. It would require us all to be a little smarter than the Norwegians. We'd put a tax not on carbon emission at the end of the pipeline, but on energy production where the pipe begins. The tax would be proportional to the real cost of environmental damage. Zero for energy efficiency. Small for renewables. More for natural gas with biological carbon sequestration (trees and compost); still more for the deep sequestration described in the Scientific American article; and more yet if there is no sequestration. Highest of all for oil, coal, and nuclear.
That may look like a tax, and it could substitute for other taxes, but it really is a fix of a market fault. It takes very real costs, which someone has to pay somewhere sometime -- the cost of climate change, air pollution, acid rain -- and puts those costs into the price of energy where they belong. Polluters pay. Carbon sequestration becomes economic everywhere, as does solar power, and above all energy efficiency. SUVs get 100 miles a gallon or run on hydrogen or both.
A magic bullet in the economy helps all the technological bullets zero in on all the right targets.
Donella H. Meadows是永續發展研究所(the Sustainable Institute )所長暨達特茅斯學院(Dartmouth)環境研究教授
全文及圖片詳見http://www.gristmagazine.com/grist/citizen/citizen022800.stm
