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April 22, 2008
Cloudy Sky, Location Unknown, 2004
Photograph by Peter Essick
Piles of cotton-like cumulus clouds fill the sky on a clear day. Mid-level cumulus clouds form between 6,500 feet (2,000 meters) and about 20,000 feet (6,000 meters). They form when humid air cools enough for water vapor to condense into droplets or ice crystals. A single cloud can hold billions of pounds of water, but may not always produce rain.
Earth Day, celebrated annually on April 22, marks the anniversary of the 1970 birth of the environmental movement. Scientists warn that rising temperatures worldwide could fuel extreme weather—just one of many damaging effects of global warming.
意译:堆积像棉花似的积云充满在晴朗的天空。中水平的堆积云从6500英尺(2000米)到20000英尺(6000米)之间。它们的构成当湿润的冷空气充足使得水蒸气浓缩成为小滴或冰晶。单一的云层能够拥有十亿磅的水,但不可能总是引起降雨。
地球日,著名的一年一次在4月22日,标志的周年纪念在1970年诞生的保护环境的运动。科学家发出警告:全世界的温度的上升燃料能造成极端的气候――其中之一正好是许多有破坏性的产生全球的变暖。
引自:“美国国家地理杂志”,当天的图片。(2008-4-22)