Ocean Acidification: 'Evil Twin' Threatens World's Oceans The rise in human emissions of carbon dioxide is driving erous changes in the chemistry and ecosystems of the world's oceans, international marine（海洋的）scientists have warned. 'Ocean conditions are already more extreme than those experienced by marine organisms and ecosystems for millions of years,' says the latest issue of the journal Trends in Ecology and Evolution. 'This emphasizes the urgent need to adopt policies that markedly reduce CO2 emissions.' Ocean acidification, which the researchers call the 'evil twin of global warming', is caused when the CO2 emitted by human activity, mainly burning fossil fuels, dissolves into the oceans. It is happening independently of, but in combination with, global warming. Evidence gathered by scientists over the last few years suggests that ocean acidification could represent an equal -- or perhaps even greater threat -- to the biology of our planet than global warming. More than 30% of the CO2 released from burning fossil fuels, cement production, deforestation and other human activities goes straight into the oceans, turning them gradually more acidic. 'The resulting acidification will impact many forms of sea life, especially organisms whose shells or skeletons are made from calcium carbonate（碳化钙）, like corals and shellfish. It may interfere with the reproduction of plankton species which are a vital part of the food web on which fish and all other sea life depend,' he adds. The scientists say there is now persuasive evidence that mass extinctions in past Earth history, like the 'Great Dying' of 251 million years ago and another wipeout 55 million years ago, were accompanied by ocean acidification, which may have delivered the deathblow to many species that were unable to cope with it. 'These past periods can serve as great lessons of what we can expect in the future, if we continue to push the acidity the ocean even further' said lead author, Dr. Carles Pelejero, from ICREA and the Marine Science Institute of CSIC in Barcelona, Spain. 'Given the impacts we see in the fossil record, there is no question about the need to immediately reduce the rate at which we are emitting carbon dioxide in the atmosphere,' he said further. 'Today, the suce waters of the oceans have already acidified by an average of 0.1 pH units from pre-industrial levels, and we are seeing signs of its impact even in the deep oceans,' said co-author Dr. Eva Calvo, from the Marine Science Institute of CSIC in Spain. 'Future acidification depends on how much CO2 humans emit from here on -- but by the year 2100 various projections indicate that the oceans will have acidified by a further 0.3 to 0.4 pH units, which is more than many organisms like corals can stand,' Prof. Hoegh-Guldberg says. 'This will create conditions not seen on Earth for at least 40 million years.' 'These changes are taking place at rates as much as 100 times faster than they ever have over the last tens of millions of years' Prof. Hoegh-Guldberg says. Besides directly impacting on the fishing industry and its contribution to the human food supply at a time when global food demand is doubling, a major die-off in the oceans would affect birds and many land species and change the biology of Earth as a whole profoundly, Prof. Hoegh-Guldberg adds. 67. What is the biggest cause of the ocean acidification according to the report? A. the increase of carbon dioxide emission by human beings B. The worsening of global warming C. The disappearance of the world’s forests D. The decrease of marine life 68. In what way according to the report does ocean acidification affect the majority of marine life? A. It affects their reproduction          B. It destroys their food chain C. It affects the growth of their young    D. destroys their habitats 69. Which of the following statements is NOT true about ocean acidification? A. Ocean acidification has made ocean conditions most extreme in millions of years. B. Ocean acidification may do more damage than global warming to human and plant life in the long run. C. Ocean acidification is suspected of having caused mass extinctions of life in past Earth history. D. The effects of ocean acidification are not now but will be felt in the foreseeable future. 70. From the report we can clearly feel that the situation with ocean acidification __________. A. is quite optimistic                B. remains well under control C. looks more than urgent            D. is already out of control