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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

admin2013-01-19  47
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.
According to the author, what may chiefly be responsible for the temperature increases ______ observed over the past century?
选项 A、Increases of daily maximum temperatures.
B、Decreases of daily minimum temperatures.
C、Increases of diurnal temperature range.
D、Decreases in the diurnal temperature range.
答案D
解析 通过上个世纪的观察，每日温差缩小是气温上升的主要原因。作者在最后一段开头说，根据上个世纪的观察，地球表面平均温度上升0.5℃，其部分原因在于每日最高气温和最低气温的差异性变化，使每日的温差缩小。
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