【李寧怡╱綜合外電報導】全球暖化嚴重，英國知名科學家認為目前抑制排放二氧化碳的方法緩不濟急，建議採行激進作法：在海洋中豎立大量巨型水管，抽取海底充滿養分的低溫海水送上海面、促進藻類生長，吸收大氣中的二氧化碳。不過也有科學家對此表達疑慮。
英國
英國知名生態學者拉伍洛克（James Lovelock）與倫敦科學博物館館長雷普利（Chris Rapley），在最新一期的《自然》（Science）期刊發表文章提出此項構想。依據兩人初步計算，這項計劃約需要在海中垂直放置一萬至十萬根直徑約10公尺、長100公尺的大型水管。
當水管隨海浪上下起伏，管中設置的單向閥會迫使海水往上流動，將海洋底層較冷海水送上表面，加速海面藻類繁殖。
科學家憂傷害生態
這些藻類除了吸收二氧化碳之外，還會製造化學物質硫化甲基，有助於形成可反射日光的雲層，降低地球溫度。
兩位科學家已經在實驗室初步證實此概念的潛在可行性，目前已獲贊助者支持，準備在海洋中進行實驗。兩人希望先在墨西哥灣與澳洲東北方的珊瑚海進行這項海洋水管計劃，因為降低海面水溫有助降低墨西哥灣颶風能量，也可復育大堡礁表面的珊瑚。
不過有科學家擔心擾亂海水循環恐傷害海洋生態；麻省理工學院環境工程學家齊休姆則指出，海洋深層水被送上海面後，要先釋出較多二氧化碳，才能開始吸收二氧化碳，一來一回間，可能有更多二氧化碳被釋放到大氣中。
James Lovelock's plan to pump ocean water to stop climate change
By Roger Highfield, Science Editor
Last Updated: 6:01pm BST 26/09/2007
A plan to save our world from extreme climate change by pumping cold water from the depths of the oceans is outlined today by James Lovelock, the scientist who inspired the greens.
James Lovelock is best known for his ideas that portray Earth as a living thing, a super-organism - named Gaia, after the ancient Earth goddess - in which creatures, rocks, air and water interact in subtle ways to ensure the environment remains stable.
Today Lovelock, of Green College, Oxford University, outlines an emergency way to stimulate the Earth to cure itself with Chris Rapley, former head of the British Antarctic Survey who is now the director of the Science Museum, London.
They believe the answer lies in the oceans, which transport much more heat than the atmosphere and, covering more than 70 per cent of the Earth's surface.
They propose that vertical pipes some 10 metres across be placed in the ocean, such that wave motion would pump up cool water from 100-200 metres depth to the surface, moving nutrient-rich waters in the depths to mix with the relatively barren warm waters at the ocean surface.
This would fertilise algae in the surface waters and encourage them to bloom, absorbing carbon dioxide greenhouse gas while also releasing a chemical called dimethyl sulphide that is know to seed sunlight reflecting clouds.
"Such an approach may fail, perhaps on engineering or economic grounds", they say, adding that the effects on the acidity of the ocean also have to be factored in.
None the less, "the removal of 500 gigatons (500 billon tons) of carbon dioxide from the air by human endeavour is beyond our current technological capability. "If we can't 'heal the planet' directly, we may be able to help the planet heal itself."
One version of the scheme sees around 10,000 pipes in the Gulf of Mexico, they told The Daily Telegraph. But until there are some trials, "there is no way one can come up with a figure on atmospheric carbon dioxide reduction per pipe let alone temperature reduction," said Dr Rapley.
"The whole idea is to stimulate some action to find out," he said. "To get an idea of orders of magnitude, the net drawdown of the ocean is estimated to be 2 gigatons per year (compared with human emissions of eight gigatons per year), but only part of that is by the biological pump we are seeking to enhance, and only a fraction of that (maybe as low as 10 per cent) finally sinks to the bottom and is trapped in the sediments (although holding it in the deep ocean helps for a while).
"So one would have to work hard to get a net sequestration of a gigaton a year - but every little helps. "
Lovelock added: "Let's not be pessimistic about the possibilities of the pipes or they might never be tried. Do not forget that they cool the top layer as well as fertilizing it.
"In the Gulf this alone may be important for reducing the severity of hurricanes. It is local self interest such as hurricane prevention and the restoration of fisheries that may pay for the project."
And they conclude in Nature: "The stakes are so high that we must try such schemes, even if they may fail.
"The Earth is fast becoming a hotter planet than anything yet experienced by humans," they write, explaining that natural processes that would normally regulate climate are being driven to amplify warming, so that higher temperatures can, for example, stimulate the release of more methane from wetlands and amplify the warming.
"Such feedbacks, as well as the inertia of the Earth system and that of our response, make it doubtful that any of the well-intentioned technical or social schemes for carbon dieting will restore the status quo.
"We need a fundamental cure for the pathology of global heating. Emergency treatment could come from stimulating the Earth's capacity to cure itself."
Scientists have put forward several proposals to reduce the amount of solar radiation that reaches the planet's surface, including the use of light-reflecting sulphate particles in the atmosphere and installing mirrors in orbit around the planet.
Using radical techniques to "engineer" Earth's climate by blocking sunlight could cool our overheated planet but present great risks that could well worsen global warming should they fail or be discontinued, warned one recent study by Ken Caldeira of the Carnegie Institution's Department of Global Ecology.
"Geoengineering schemes have been proposed as a cheap fix that could let us have our cake and eat it, too. But geoengineering schemes are not well understood. Our study shows that planet-sized geoengineering means planet-sized risks."
However, Dr Rapley said in response: "The attraction of this approach is that the dangers of "unexpected consequences" are low, because we are advocating stimulating and enhancing an entirely natural process."
Prof Sir Brian Hoskins, Professor of Meteorology at University of Reading, commented: "This is the latest in a line of geo-engineering "solutions" or rather "buying time".
"As with some of the others, there is certainly a strong scientific basis for the proposal. Also I agree that the current global political inaction on the climate issue is very serious.
"In my opinion our uncertainties over the likely regional impact of what our greenhouse gas emissions may do is high. The uncertainties over what these "solutions" may do is an order of magnitude higher.
"However we must make sure that our understanding of the climate system and our ability to model it increase as fast as possible so that we can be very confident about the former, the greenhouse gas emissions, and confident about the latter, the "solutions".
"As a different issue the sheer practicality of doing the proposed "solutions" on the required scale to combat greenhouse emissions also has to be considered.
"One of the nightmares is that commercial companies may offer to off-set people's carbon emissions by doing them on a smaller scale, with no real knowledge of the wider implications."
