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Unit 4 Weather and Climate 天气与气候
passage (2/4)
Hints:
60F
Without this natural "greenhouse effect", temperatures would be much lower than they are now, and life as known today would not be possible. Thanks to greenhouse gases, the earth's average temperature is a more hospitable 60F. However, problems may arise when the atmospheric concentration of greenhouse gases increases.
Scientists generally believe that the combustion of fossil fuels and other human activities are the primary reason for the increased concentration of carbon dioxide. What has changed in the last few hundred years is the additional release of carbon dioxide by human activities. Fossil fuels burned to run cars and trucks, heat homes and businesses, and power factories are responsible for about 98% of US carbon diozide emissions, 24% of methane emissions,and 18% of nitrous oxide emissions. |
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发表于 2016-8-2 11:36:35