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Why Do Mountains Have Snow on Top All Year?
为什么高山顶部常年积雪？
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Air gets colder as you go higher in the atmosphere.大气层中，海拔越高，气温越低。
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Mountain tops stay below freezing even in summer months.即使在夏季，山顶温度也常年低于冰点。
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Snow falls often and melts very slowly due to low temperatures.降雪频繁，且因气温低而融化极慢。
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Strong winds also blow snow into sheltered spots where it builds up.强风还将积雪吹入背风处堆积。
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Over years, snow compacts into ice and forms glaciers.经年累月，积雪压实成冰，形成冰川。
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Sunlight reflects off white snow, keeping the area cooler.阳光被白雪反射，使当地保持低温。
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This cold zone is called the 'snow line'—it rises near the equator.这一寒冷区域称为‘雪线’，在赤道附近位置更高。
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Climate change is now raising this line higher each decade.气候变化正使这条雪线每十年持续升高。