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  3. The climate of Earth is changing. Climatologists are confident that over the past century, the global average surface temperatur

The climate of Earth is changing. Climatologists are confident that over the past century, the global average surface temperatur

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问题     The climate of Earth is changing. Climatologists are confident that over the past century, the global average surface temperature has increased by about half a degree Celsius. This warming is thought to be at least partly the result of human activities, such as the burning of fossil fuels and the clearing of forests for agriculture. As the global population grows and national economies expand, the global average temperature is expected to continue increasing by an additional 1.0 to 3.5°C by the year 2100.
    Climate change is one of the most important environmental issues facing humankind. Understanding the potential impacts of climate change for natural ecosystems is essential if we are going to manage our environment to minimize the negative consequences of climate change and maximize the opportunities that it may offer. Because natural ecosystems are complex, nonlinear systems, it follows that their responses to climate change are likely to be complex. Climate change may affect natural ecosystems in a variety of ways. In the short term, climate change can alter the mix of plant species in land ecosystems such as grasslands. In the long term, climate change has the potential to dramatically alter the geographic distribution of major vegetation types — savannas, forests, and tundra. Climate change can also potentially alter global ecosystem processes, including the cycling of carbon, nitrogen, phosphorus, and sulfur. Moreover, changes in these ecosystem processes can affect and be affected by changes in the plant species of the ecosystem and vegetation type. All of the climate change-induced alterations of natural ecosystems affect the services that these ecosystems provide to humans.
    The global average surface temperature increase of half a degree Celsius observed over the past century has been in part due to differential changes in daily maximum and minimum temperatures, resulting in a narrowing of the diurnal temperature range. Decreases in the diurnal temperature range were first identified in the United States, where large-area trends showed that maximum temperatures have remained constant or increased only slightly, whereas minimum temperatures have increased at a faster rate. In this issue, Alward’s report on the different sensitivities of rangeland plants to minimum temperatures increases.
The second paragraph is primarily concerned with______.
选项 A、the potential impacts of climate change for natural ecosystems
B、how to minimize the negative consequences of climate change
C、how to maximize the opportunities that climate change may offer
D、the complex, nonlinear nature of natural ecosystems
答案A
解析 本题的四个选项中，只有A项为正确答案。这可从文中第二段的内容推知，即对人类来说，气候变化是众多重要环境问题之一。后面又分析了气候变化会带来的诸多影响和后果，特别是对生态环境的影响。
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