大气储存热量的能力被普遍看作是“温室效应”。尽管公众对于全球气候变暖这一问题存在争议，但是在科学界，自然的温室效应问题很久前就被看作是事实了。确实，如果不是因为云层、水蒸气、二氧化碳以及其他气体对热量的储存，地球的自然温度应该比现在低33度，生命在那种气候条件下的进化将会大不一样。

　　大多数科学家相信，在过去几百年里农业和工业的迅速发展使得大气中二氧化碳和甲烷的含量迅速增加。然而，对于这些改变是否是造成地球表面温度比上个世纪增加了大约0.5摄氏度的原因，专家们持不同意见。许多科学家引述了这样一个事实：1997年是有气象记录以来最热的一年，之前的十年里有九年排在本世纪温度最高的前11名里，这充分且有力地证明了人类活动已经改变了地球的气候。但是另外一些科学家却认为这种温度变化趁势是自然变化。

　　另一个争议是关于世界计划人口到2100年突 破 100亿是否会使大气中二氧化碳含量增加一倍到两倍?许多科学家预测说如果这种情况真的发生的话，下个世纪世界各地的气温都将升高，升高程度从一度到四度不等。这个温度变化范围中最大的部分比从上个冰河时代末期到现在的10000年间人类经历的温度变化还要大。在上一个冰河时期，全球平均气温只比现在低5 摄氏度。

　　温度升高几度会造成海平面升高10厘米到1米不等。海平面上升0.5米对于处在低地的岛屿和沿海地区来说就相当危险了。海平面再升高一些就会给低地的海滩、湿地、和沿海居民带来特大洪灾。而且，海平面升高就会增加沿海地区发生灾难性暴风雨的可能性，因为洪水可能会以前所末有的强度登陆。

　　温度升高还会加剧一些地方的干旱，破坏生态平衡，造成一些物种数量的减少甚至灭绝。由于二氧化碳能促进光合作用，所以一些科学家估计大气中二氧化碳含量的增加会提高庄稼的产量并且促进森林生长。但是另外一些科学家则指出二氧化碳的增加和气候变暖会使得具有破坏性的害虫、杂草以及携带疾病的昆虫大规模扩散。

　　【参考译文】

　　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.