46 What is the main idea of this article?
(A)Public reactions toward global warming and the greenhouse effects.
(B)How human beings cause global warming.
(C)Global warming and greenhouse effects on earth.
(D)Solutions of global warming and greenhouse effects.

 Throughout its long history, Earth has warmed and cooled time and again. Climate has changed when the planetreceived more or less sunlight due to subtle shifts in its orbit, as the atmosphere or surface changed, or when the Sun’senergy varied. 

在其悠久的歷史中，地球一次又一次地變暖和變冷。當行星由於其軌道的細微變化，大氣或地表的變化或太陽的能量變化而受到或多或少的陽光照射時，氣候就發生了變化。

 Global warming is the unusually rapid increase in Earth’s average surface temperature over the past centuryprimarily due to the greenhouse gases released as people burn fossil fuels. The global average surface temperature rose 0.6 to 0.9 degrees Celsius (1.1 to 1.6°F) between 1906 and 2005, and the rate of temperature increase has nearlydoubled in the last 50 years. Temperatures are certain to go up further. 

 全球變暖是過去一個世紀以來地球平均表面溫度異常迅速的上升，主要原因是人們燃燒化石燃料時釋放的溫室氣體。從1906年到2005年，全球平均表面溫度上升了0.6到0.9攝氏度（1.1到1.6°F），在過去50年中，溫度的上升速度幾乎翻了一番。溫度肯定會進一步上升。

 Earth’s temperature begins with the Sun. Roughly 30 percent of incoming sunlight is reflected back into space bybright surfaces like clouds and ice. Of the remaining 70 percent, most is absorbed by the land and ocean, and the rest isabsorbed by the atmosphere. The absorbed solar energy heats our planet. As the rocks, the air, and the seas warm, theyradiate “heat” energy (thermal infrared radiation). From the surface, this energy travels into the atmosphere wheremuch of it is absorbed by water vapor and long-lived greenhouse gases such as carbon dioxide and methane. Whenthey absorb the energy radiating from Earth’s surface, microscopic water or greenhouse gas molecules turn into tinyheaters— like the bricks in a fireplace, they radiate heat even after the fire goes out. They radiate in all directions. Theenergy that radiates back toward Earth heats both the lower atmosphere and the surface, enhancing the heating they getfrom direct sunlight. This absorption and radiation of heat by the atmosphere—the natural greenhouse effect—isbeneficial for life on Earth. If there were no greenhouse effect, the Earth’s average surface temperature would be a verychilly -18°C (0°F) instead of the comfortable 15°C (59°F) that it is today. 

地球的溫度始於太陽。大約30％的入射陽光通過雲層和冰層等明亮的表面反射回太空。在剩餘的70％中，大部分被陸地和海洋吸收，其餘被大氣吸收。吸收的太陽能加熱我們的星球。當岩石，空氣和海洋變暖時，它們會輻射“熱”能（紅外熱輻射）。該能量從表面傳播到大氣中，其中的大部分能量被水蒸氣和長壽命的溫室氣體（例如二氧化碳和甲烷）吸收。當它們吸收地球表面輻射的能量時，微小的水或溫室氣體分子會變成微小的加熱器，就像壁爐中的磚頭一樣，即使在火熄滅後也會輻射熱量。它們向各個方向輻射。輻射回地球的能量會加熱低層大氣和地表，從而增強它們從直射陽光中獲得的熱量。大氣層對熱量的吸收和輻射（自然的溫室效應）對地球上的生命有益。如果沒有溫室效應，地球的平均表面溫度將是非常涼爽的-18°C（0°F），而不是今天的15°C（59°F）舒適。

 What has scientists concerned now is that over the past 250 years, humans have been artificially raising theconcentration of greenhouse gases in the atmosphere at an ever-increasing rate, mostly by burning fossil fuels, but alsofrom cutting down carbon-absorbing forests. Since the Industrial Revolution began in about 1750, carbon dioxidelevels have increased nearly 38 percent as of 2009 and methane levels have increased 148 percent. The atmospheretoday contains more greenhouse gas molecules, so more of the infrared energy emitted by the surface ends up beingabsorbed by the atmosphere. Since some of the extra energy from a warmer atmosphere radiates back down to thesurface, Earth’s surface temperature rises.
 現在，科學家們擔心的是，在過去的250年中，人類一直在以不斷增加的速度人為地提高溫室氣體的濃度，主要是通過燃燒化石燃料，還通過砍伐吸收碳的森林。自大約1750年工業革命開始以來，截至2009年，二氧化碳含量增加了近38％，甲烷含量增加了148％。如今的大氣中含有更多的溫室氣體分子，因此，表面釋放出的更多紅外能量最終被大氣吸收。由於來自更溫暖的大氣的一些額外能量向下輻射回地面，因此地球的表面溫度會升高。

 Throughout its long history, Earth has warmed and cooled time and again. Climate has changed when the planet received more or less sunlight due to subtle shifts細微的變化 in its orbit, as the atmosphere or surface changed, or when the Sun’s energy varied. 

     Global warming is the unusually rapid increase in Earth’s average surface temperature over the past century primarily due to the greenhouse gases released as people burn fossil fuels. The global average surface temperature rose 0.6 to 0.9 degrees Celsius (1.1 to 1.6°F) between 1906 and 2005, and the rate of temperature increase has nearly doubled in the last 50 years. Temperatures are certain to go up上升 further. 

     Earth’s temperature begins with the Sun. Roughly 30 percent of incoming sunlight is reflected back into space by bright surfaces like clouds and ice. Of the remaining 70 percent, most is absorbed by the land and ocean, and the rest is absorbed by the atmosphere. The absorbed solar energy heats our planet. As the rocks, the air, and the seas warm, they radiate “heat” energy (thermal infrared radiation). From the surface, this energy travels into the atmosphere where much of it is absorbed by water vapor水汽，汽，蒸汽 and long-lived 長久的greenhouse gases such as carbon dioxide and methane. When they absorb the energy radiating from Earth’s surface, microscopic water or greenhouse gas molecules turn into tiny heaters— like the bricks in a fireplace壁爐, they radiate heat even after the fire goes out. They radiate in all directions. The energy that radiates back toward Earth heats both the lower atmosphere and the surface, enhancing the heating they get from direct sunlight. This absorption and radiation of heat by the atmosphere—the natural greenhouse effect—is beneficial for life on Earth. If there were no greenhouse effect, the Earth’s average surface temperature would be a very chilly -18°C (0°F) instead of the comfortable 15°C (59°F) that it is today. 

     What has scientists concerned now is that over the past 250 years, humans have been artificially raising the concentration of greenhouse gases in the atmosphere at an ever-increasing rate, mostly by burning fossil fuels, but also from cutting down carbon-absorbing forests. Since the Industrial Revolution began in about 1750, carbon dioxide二氧化物 levels have increased nearly 38 percent as of 2009 and methane甲烷，沼氣 levels have increased 148 percent. The atmosphere today contains more greenhouse gas molecules, so more of the infrared紅外線 energy emitted by the surface ends up being absorbed by the atmosphere. Since some of the extra energy from a warmer atmosphere radiates back down to the surface, Earth’s surface temperature rises.