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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℃ 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 temperature have increased at a faster rate. In this issue, Alward et al. 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 作者在第二段指出，气候变化可能在许多方面影响自然生态系统。在短期内，气候变化能够改变陆地生态系统，如草原上的植物物种的成分比例。从长远的观点来看，气候变化有可能大大地改变主要植被——如大草原、森林和苔原的地理分布。气候变化还有可能改变全球生态系统的变化过程，包括碳、氮、磷和硫的循环过程。
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