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(回答先: 地球温暖化のタイムテーブル〔Independent〕 投稿者 ネオファイト 日時 2005 年 2 月 09 日 12:01:47)
二酸化炭素が海水に溶けることによりアルカリ性の海水がわずかに酸性側に傾く。水素イオン濃度を示すpHで8.2（弱アルカリ）だったのが8.1（弱アルカリ）へと変化してきており、海水のpHの減少傾向は続いている。水素イオン濃度は生態系が何万年とかけて平衡状態に保ってきたものだが、この平衡が崩れることで海洋中の炭酸を固化する役割を持つプランクトンや甲殻類とそれを餌とする魚、珊瑚やそこを住処とする魚など、多くの種が危険に晒される可能性が指摘されている。また海洋の炭酸を固化する役割が損なわれた場合には一層の大気の二酸化炭素濃度の上昇等も危惧される。
http://www.guardian.co.uk/life/science/story/0,12996,1405811,00.html
Scientists warn growing acidity of oceans will kill reefs
Paul Brown, environment correspondent
Friday February 4, 2005
The Guardian
Scientists have given warning of a newly discovered threat to mankind, which will wipe out coral and many species of fish and other sea life.
Extra carbon dioxide in the air, caused by the burning of fossil fuels, is not only spurring climate change, but is making the oceans more acidic - endangering the marine life that helps to remove carbon dioxide from the atmosphere.
So alarmed have marine scientists become about this that special briefings have been held for government departments. Carol Turley, head of science at Plymouth Marine Laboratory, warned of a "potentially gigantic" problem for the world.
"It is very urgent to warn people what is happening," she said. "Many of the species we rely on to eat, like cod, will disappear. In cartoon form, you could say people should prepare to change their tastes and switch from cod and chips to jellyfish and chips. The whole composition of life in the oceans will change."
Jerry Blackford, another of the authors of a paper presented to a climate change conference in Exeter, has modelled the effect on the oceans. He said: "Some scientists are saying that, in 35 years, all the coral reefs in the world could be dead - it could be less or more. Put it this way, my children may never get the opportunity to go snorkelling on a living reef. Certainly, my grandchildren won't."
Although the phenomenon is caused by excess carbon dioxide in the atmosphere, it is not a "global warming" problem, but a simple chemical reaction between air and sea.
Carbon dioxide mixed with water produces carbonic acid which is making the alkaline oceans more acidic. But for hundreds of thousands and probably millions of years plankton, shellfish and corals have adapted to use the stable levels of calcium and carbon in the sea to make their shells.
"Scientists did not look at this problem because everyone assumed the chemical composition of the sea was constant. But this change is 'O-level' chemistry and we missed it," said Dr Turley.
The oceans' vital role in limiting CO2 levels in the air will have to be reassessed in light of the findings.
Plankton are as important as plants and trees in the take-up of carbon. Scientists estimate that about half the 800 billion tonnes of CO2 put into the atmosphere by mankind since the start of the industrial revolution has been soaked up by the sea. Much of the carbon is fixed in the shells of creatures called coccolithphores, the tiny plankton whose bodies make up the white cliffs of Dover. They live on the ocean surface in trillions and when they die their shells sink to the bottom taking the carbon with them. They could not survive in a more acidic sea and their removal of carbon from the atmosphere would stop.
"These creatures are part of our survival bubble. The oceans give us a sustainable atmosphere by taking out the carbon dioxide. They're the lungs of the planet. People have not woken up to the potential impact their removal will cause," said Dr Turley.
The acidity of liquid is measured on the pH scale, from one to 14, with seven being neutral, and the higher the number the more alkaline. The oceans have previously recorded an 8.2 pH reading, but this has now dropped to 8.1 and is continuing to fall.
The sea around Britain has been found to be more acid than many other areas, partly because of ocean currents, but mainly because Europe and North America are the largest carbon dioxide emitters.
Experiments show that even a small increase in acidity reduces the ability of shellfish and plankton to grow and causes a population fall.
The loss of corals would seriously affect small islands and coasts.
The fundamental problem is the effect on the food chain. Zooplankton, essential food for fish, could suffer increasing mortality rates and starfish, whelks and other shellfish, eaten by cod, might perish.
This might lead to population explosions of other creatures, such as jellyfish, or crabs, shrimps and lobsters which rely on chitin rather than calcium for their shells.
The Royal Society has set up a working group to study the problem. Plymouth Marine Laboratory is installing special tanks to aid the research.
The conference on avoiding dangerous climate change was held at the Meteorological Office in Exeter. At its conclusion, the steering committee of senior scientists identified the growing acidity of the oceans as a new impact that was "potentially disturbing". It would reduce the oceans' capacity to remove CO from the atmosphere and affect the entire marine food chain.
Participants at the conference also concluded that the risks from rising temperatures were "more serious than previously thought".
04 February 2005
Gigantic changes to the oceans, leading to the extinction of marine life from cod to coral reefs, are likely because of the main greenhouse gas causing global warming, British scientists warned yesterday.
Researchers have found a new and potentially devastating danger from the huge volumes of carbon dioxide (CO2) produced by industry and transport, already threatening the planet with climate change.
Now, they warn, it is also rapidly turning the world's oceans acid as it is dissolved in seawater, and putting an enormous array of marine life at risk. Ocean acidification may wipe out much of the microscopic plankton at the base of the marine food web, and have a knock-on fatal effect up through shellfish to major human food species such as cod. It is already having a serious impact on organisms such as coral, and putting a question mark against the future of coral reefs.
The findings about acid seas, which are recent, are causing alarm in the international scientific community because they represent a huge threat to the world until now unknown.
They were set out in detail at the conference on climate change at the Met Office headquarters in Exeter, in a paper by scientists from Britain's Plymouth Marine Laboratory. Sir David King, the chief scientific adviser, who will be reporting on the conference to Tony Blair, said: "This is the first time it [the research] has been pulled together. I think it is very serious."
Dr Carol Turley, the Plymouth laboratory's head of science, who presented the paper, said ocean acidification represented "potentially a gigantic problem for the world". She added: "It's urgent indeed to warn people what's happening. Many of the marine species we rely on to eat could well disappear. In cartoon terms, you could say people should prepare to change their tastes, and switch from cod and chips, to jellyfish and chips."
Remarkably, the findings about acidifying seas constituted the second revelation of a new global danger at the conference, which was called by the Prime Minister as part of Britain's efforts to focus attention on climate change during the UK presidency of the G8 group of rich nations and the European Union. On Tuesday, the head of the British Antarctic Survey, Professor Chris Rapley, disclosed that the vast West Antarctic ice sheet, previously thought to be stable, may be beginning to disintegrate, which would cause a sea-level rise around the world of more than 16ft. Although a growing number of studies about ocean acidification have been done, it is only recently that the whole picture has been put together, and stark nature of the threat appreciated. "The world scientific community is only just waking up to this," said Dr Turley, who with her colleagues has spent weeks briefing senior scientists on the problem in a range of government bodies from English Nature to the Department of Trade and Industry.
The world's oceans have always taken up and given off large volumes of naturally occurring carbon dioxide as part of the carbon cycle. But since the Industrial Revolution, the amounts have greatly increased, now more rapidly. The scientists believe 400 billion tons of man-made CO2 - half that produced - have been taken up by the seas, and much more is going in as the world economy relentlessly expands.
But the extra volumes are now causing a simple chemical reaction with the seawater - "O-level chemistry," Dr Turley said - in which the CO2 and the water (H2O) react to produce carbonic acid (HCO3). This is changing the chemical composition of the sea from slightly alkaline to acidic, producing an environment in which many vital organisms may not survive.
If, for example, the plankton on which cod larvae feed disappear, the cod will go, and something else, perhaps jellyfish, will move into their niche in the ecosystem.
Trials on organisms grown in seawater with raised CO2 levels, from plankton to scallops, indicate many species are likely to be affected. The increasing acidification is affecting coral already and another paper at the conference suggested that in 30 years all the world's coral reefs may be dying because of it.
The conference closed last night, with a statement saying: "In many cases, the risks are more serious than previously thought. This is likely to affect the entire marine food chain."
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