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  3. At noon on May 4th the carbon-dioxide concentration in the atmosphere around the Mauna Loa Observatory in Hawaii hit 400 parts p

At noon on May 4th the carbon-dioxide concentration in the atmosphere around the Mauna Loa Observatory in Hawaii hit 400 parts p

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问题     At noon on May 4th the carbon-dioxide concentration in the atmosphere around the Mauna Loa Observatory in Hawaii hit 400 parts per million (ppm). The average for the day was 399.73 and researchers at the observatory expect this figure, too, to exceed 400 in the next few days. The last time such values prevailed on Earth was in the Pliocene epoch (上新世) 4m years ago, when jungles covered northern Canada.
    There have already been a few readings above 400 ppm elsewhere—those taken over the Arctic Ocean in May 2012, for example—but they were exceptional. Mauna Loa is the benchmark (标准) for CO2 measurement because Hawaii is so far from large concentrations of humanity. The Arctic, by contrast, gets a lot of polluted air from Europe and North America.
    The concentration of CO2 peaks in May, falls until October as plant growth in the northern hemisphere’s summer absorbs the gas, and then goes up again during winter and spring. This year the average reading for the whole month will probably also reach 400 ppm, according to Pieter Tans, who is in charge of monitoring at Mauna Loa, and the seasonally adjusted annual figure will reach 400 ppm in the spring of 2014 or 2015.
    Mauna Loa’s readings are one of the world’s longest-running measurement series. The first, made in March 1958, was 315 ppm. That means they have risen by a quarter in 55 years. In the early 1960s they were going up by 0.7 ppm a year. The rate of increase is now 2.1 ppm—three times as fast—reflecting the relentless rise in green-house-gas emissions.
    As a rule of thumb, CO2 concentrations will have to be restricted to about 450 ppm if global warming is to be kept below 2 degrees. Because CO2 stays in the atmosphere for decades, artificial emissions of the gas would have to be cut immediately, and then fall to zero by 2075, in order to achieve 450 ppm. There seems no chance of that. Emissions are still going up. At current rates, the Mauna Loa reading will rise above 450 ppm in 2037.
We can learn from the first paragraph that ______.
选项 A、Mauna Loa Observatory is located in northern Canada
B、about 4 million years ago, jungles covered northern part of the Earth
C、the carbon-dioxide concentration is expected to exceed 400 ppm in the next few days
D、it is the first time in human history that carbon-dioxide concentration reaches 400 ppm
答案C
解析 根据选项A中的“Mauna Loa”定位到首句：...the Mauna Loa Observatory in Hawaii…说明Mauna Loa是在夏威夷而不是加拿大。根据选项B定位到尾句：...4m years ago, when jungles covered northern Canada. 故B项错误。C项对应原文：...researchers at the observatory expect this figure, too, to exceed 400 in the next few days. 而“this figure”指代的就是“carbon-dioxide concentration”，故正确。D项对应原文：The last time such values prevailed on Earth was in the Pliocene epoch 4m years ago… 说明达到400 ppm这个数据不是历史上第一次。综上所述，该题答案为选项C。
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