The Greenhouse effect and Global warming
　　The heart-trapping capacity of the atmosphere is popularly known as the “greenhouse effect”. Despite public controversy surrounding global warming, the natural greenhouse effect has been long established as fact in the scientific community.
　　Indeed, carbon dioxide, and other gases, the earth’s natural climate would be about 33℃ cooler than it is. Life would have evolved quite differently in such a climate.
　　Most scientists believe that the rapid expansion of agriculture and industrial activities over the last several hundred years have generated significant increases in carbon dioxide and methane in the atmosphere. However, experts disagree about whether such changers have caused the increase of approximately 0.5℃ in the earth’s surface temperature that has been documented over the past century. Many scientists cite the fact that 1997 was the warmest year on record, following a decade in which 9 of the 11 hottest years of this century were reported, as strong, but circumstantial, evidence that human activities have altered the earth’s climate. Other experts, however, believe this temperature trend is a natural variation.
　　Also disputed is whether projectedworld population growth to more than 10 billion people by the year 2100 will result in a doubling or tripling of atmospheric concentrations of carbon dioxide. If such a buildup occurs, as many scientists predict, global surface temperatures could increase by anywhere from about one Celsius degree to about 4 Celsius degrees during the next century. The higher half of range involves temperature changes outside of those experienced by human civilizations since the end of the last ice age some 10,000 years ago. During the last ice age, average global temperatures were only about 5 Celsius degrees cooler than the present period.
　　A temperature increase of several degrees Celsius could result in a sea level rise ranging from about 10 cm to about 1 m. A sea level rise of about 0.5 m would be noticeable primarily in the most vulnerable, low-lying islands and coastal areas. Larger sea level rises would result in extensive flooding of lowland beaches, wetlands, and coastal settlements. Moreover, a higher sea level base would increases the risk of catastrophic storm surges in coastal areas, since flooding would likely extend island well beyond historic levels.
　　Warmer temperature could also intensify droughts in some regions, destabilize ecosystems, and cause the decline or extinction of some species. Since carbon dioxide enhances photosynthesis, some scientists have calculated that higher concentrations in the atmostphere would increase the productivity of crops and forests. But others have point out that carbon dioxide increase and a warming climate could encourage the spread of destructive pests, including weeds and disease-carrying insects.
　　參考譯文：
　　大氣儲存熱量的能力被普遍看作是“溫室效應”。盡管公眾對于全球氣候變暖這一問題存在爭議，但是在科學界，自然的溫室效應問題很久前就被看作是事實了。確實，如果不是因為云層、水蒸氣、二氧化碳以及其他氣體對熱量的儲存，地球的自然溫度應該比現在低33度，生命在那種氣候條件下的進化將會大不一樣。
　　大多數科學家相信，在過去幾百年里農業(yè)和工業(yè)的迅速發(fā)展使得大氣中二氧化碳和甲烷的含量迅速增加。然而，對于這些改變是否是造成地球表面溫度比上個世紀增加了大約0.5攝氏度的原因，專家們持不同意見。許多科學家引述了這樣一個事實：1997年是有氣象記錄以來最熱的一年，之前的十年里有九年排在本世紀溫度最高的前11名里，這充分且有力地證明了人類活動已經改變了地球的氣候。但是另外一些科學家卻認為這種溫度變化趁勢是自然變化。
　　另一個爭議是關于世界計劃人口到2100年突破100億是否會使大氣中二氧化碳含量增加一倍到兩倍?許多科學家預測說如果這種情況真的發(fā)生的話，下個世紀世界各地的氣溫都將升高，升高程度從一度到四度不等。這個溫度變化范圍中最大的部分比從上個冰河時代末期到現在的10000年間人類經歷的溫度變化還要大。在上一個冰河時期，全球平均氣溫只比現在低5攝氏度。
　　溫度升高幾度會造成海平面升高10厘米到1米不等。海平面上升0.5米對于處在低地的島嶼和沿海地區(qū)來說就相當危險了。海平面再升高一些就會給低地的海灘、濕地、和沿海居民帶來特大洪災。而且，海平面升高就會增加沿海地區(qū)發(fā)生災難性暴風雨的可能性，因為洪水可能會以前所末有的強度登陸。
　　溫度升高還會加劇一些地方的干旱，破壞生態(tài)平衡，造成一些物種數量的減少甚至滅絕。由于二氧化碳能促進光合作用，所以一些科學家估計大氣中二氧化碳含量的增加會提高莊稼的產量并且促進森林生長。但是另外一些科學家則指出二氧化碳的增加和氣候變暖會使得具有破壞性的害蟲、雜草以及攜帶疾病的昆蟲大規(guī)模擴散。

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