“溫室效應”是指地球大氣層上的一種物理特性。假若沒有大氣層，地球表面的平均溫度不會是現在合宜的15℃，而是十分低的-18℃。這種溫度上的差別是由溫室氣體導致的，這些氣體吸收紅外線輻射而影響到地球整體的能量平衡。受到溫室氣體的 影響，大氣層吸收紅外線輻射的份量比它釋放到太空外的垛，這使地球表面溫度上升，這個過程就是“天然的溫室效應”。但由于人類活動釋放出大量的溫室氣體，結果讓更多紅外線輻射被折射到地面上，加強了“溫室效應”的作用。

全球變暖是目前全球環境研究的一個主要議題。根據對100多份全球溫度變化資料的系統分析，發現全球平均溫度已升高0.3～0.6攝氏度。其中11個最暖的年份發生在80年代中期以后，因而全球變暖是一個毋庸置疑的事實。全球變暖將帶來非常嚴重的后果，如冰川消退、海平面上升、荒漠化等等，還給生態系統、農業生產帶來嚴重影響。全球變暖現象最終可能會導致全球變冷，形成另一次冰河時代。就像我們在美國電影《后天》里面看到的可怕情景。

因此，探求全球變暖的起因成為重要的研究課題。分析表明，雖然地球演化史上曾經多次發生變暖--變冷的氣候波動，但人類活動引起的大氣溫室效應增長可能是主要因素。

各國政府、企業和科學家們逐步達成共識，大家必須迅速行動起來，與氣候變化作斗爭。目前人們已經采取措施限制二氧化碳的排放量。許多公司正積極應對二氧化碳限排時代的到來。

Part 8 El Nino and La Nina 厄爾尼諾和拉妮娜

El Nino and La Nina are opposite phases of the El Nino-Southern Oscillation (ENSO) cycle, with La Nina sometimes referred to as the cold phase of ENSO and El Nino as the warm phase of ENSO.

El Nino is a disruption of the ocean-atmosphere system in the tropical Pacific having important consequences for weather around the globe. Among these consequences are increased rainfall across the southern tier of the US and in Peru, which has caused destructive flooding, and drought in the West Pacific, sometimes associated with devastating brush fires in Australia.

In normal, non-El Nino conditions, the trade winds blow towards the west across the tropical Pacific. These winds pile up warm surface water in the west Pacific, so that the sea surface is about 1/2 meter higher at Indonesia than at Ecuador.

The sea surface temperature is about 8 degrees C higher in the west, with cool temperatures off South America, due to an upwelling of cold water from deeper levels. This cold water is nutrient-rich, supporting high levels of primary productivity, diverse marine ecosystems, and major fisheries. Rainfall is found in rising air over the warmest water, and the east Pacific is relatively dry.

During El Nino, the trade winds relax in the central and western Pacific leading to a depression of the thermocline in the eastern Pacific, and an elevation of the thermocline in the west. This reduced the efficiency of upwelling to cool the suface and cut off the supply of nutrient rich thermocline water to the euphotic zone. The result was a rise in sea surface temperature and a drastic decline in primary productivity, the latter of which adversely affected higher trophic levels of the food chain, including commercial fisheries in this region.

Rainfall follows the warm water eastward, with associated flooding in Peru and drought in Indonesia and Australia. The eastward displacement of the atmospheric heat source overlaying the warmest water results in large changes in the global atmospheric circulation, which in turn force changes in weather in regions far removed from the tropical Pacific.

Global climate La Nina impacts tend to be opposite those of El Ninno impacts. In the tropics, ocean temperature variations in La Nina tend to be opposite those of El Nino. At higher latitudes, El Nino and La Nina are among a number of factors that influence climate. However, the impacts of El Nino and La Nina at these latitudes are most clearly seen in wintertime.

In the continental US, during El Nino years, temperatures in the winter are warmer than normal in the North Central States, and cooler than normal in the Southeast and the Southwest. During a La Nina year, winter temperatures are warmer than normal in the Southeast and cooler than normal in the Northwest.

The twists and turns in the ongoing dialogue between ocean and atmosphere in the Pacific can have a ripple effect on climatic conditions in far flung regions of the globe. This worldwide message is conveyed by shifts in tropical rainfall, which affect wind patterns over much of the globe.

Imagine a rushing stream flowing over and around a series of large boulders. The boulders create a train of waves that extend downstream, with crests and troughs that show up in fixed positions. If one of the boulders were to shift, the shape of the wave train would also change and the crests and troughs might occur in different places.

Dense tropical rainclouds distort the air flow aloft 5-10 miles above sea level much as rocks distort the flow of a stream, or islands distort the winds that blow over them, but on a horizontal scale of thousands of miles. The waves in the air flow, in turn, determine the positions of the monsoons, and the storm tracks and belts of strong winds aloft, commonly referred to as jet streams, which separate warm and cold regions at the Earth's surface.

In El Nino years, when the rain area that is usually centered over Indonesia and the far western Pacific moves eastward into the central Pacific, as shown on p. 17, the waves in the flow aloft are affected, causing unseasonable weather over many regions of the globe.

近年來，各類媒體越來越關注這樣一個氣候學名詞：厄爾尼諾。眾多氣候現象與災難都被歸結到厄爾尼諾的肆虐上，例如印尼的森林大火、巴西的暴雨、 北美的洪水及暴雪、非洲的干旱等等。它幾乎成了災難的代名詞！

可是厄爾尼諾究竟是什么呢？用一句話來說：厄爾尼諾是熱帶大氣和海洋相互作用的產物，它原是指赤道海面的一種異常增溫，現在其定義為在全球范圍內，海氣相互作用下造成的氣候異常。

厄爾尼諾現象是發生在大氣環流和海洋環流之間的強耦合事件的例子。大氣環流（風）施加于海洋的應力是海洋環流的主要驅動力，同時，正如我們所看到的那樣，來自海洋的熱量，特別是蒸發作用對大氣環流有極大的影響。

厄爾尼諾現象的基本特征是赤道太平洋中東海域海水溫度異常增高。由于熱帶太平洋是一個控制大氣運動的巨大熱源和水氣源，因此厄爾尼諾現象的發生將引起全球氣候異常。

拉尼娜是指赤道太平洋東部和中部海面溫度持續異常偏冷的現象（與厄爾尼諾現象正好相反）。是氣象和海洋界使用的一個新名詞。意為“小女孩”，正好與意為“圣嬰”的厄爾尼諾相反，也稱為“反厄爾尼諾”或“冷事件”。

厄爾尼諾與赤道中、東太平洋海溫的增暖、信風的減弱相聯系，而拉尼娜卻與赤道中、東太平洋海溫度變冷、信風的增強相關聯。因此，實際上拉尼娜是熱帶海洋和大氣共同作用的產物。

拉尼娜同樣對氣候有影響。拉尼娜與厄爾尼諾性格相反，隨著厄爾尼諾的消失，拉尼娜的到來，全球許多地區的天氣與氣候災害也將發生轉變。總體說來，拉尼娜并非性情十分溫和，它也將可能給全球許多地區帶來災害，其氣候影響與厄爾尼諾大致相反，但其強度和影響程度不如厄爾尼諾。

Global environmental collapse is not inevitable. But the developed world must work with the developing world to ensure that new industrialized economies do not add to the world's environmental problems. Politicians must think of sustainable development rather than economic expansion.

Conservation strategies have to become more widely accepted, and people must learn that energy use can be dramatically diminished without sacrificing comfort. In short, with the technology that currently exists, the years of global environmental mistreatment can begin to be reversed.

科學技術以前所未有的速度和規模迅猛發展，增強了人類改造自然的能力，給人類社會帶來空前的繁榮，也為今后的進一步發展準備了必要的物質技術條件。對此，人們產生了盲目樂觀情緒，好象自己已經成為大自然的主人，可以長期掠奪資源而不會受到大自然的懲罰。然而，這種掠奪式生產已經造成了生態和生活的破壞，大自然向人類亮起了紅燈。

人們承認面臨的嚴重危機，但是可以通過共同的努力戰勝它，尋求新的發展道路。可持續發展戰略的核心是經濟發展與保護資源、保護生態環境的協調一致，讓人類子孫后代能夠享有充分的資源和良好的自然環境。可持續發展是一個長期的戰略目標，需要人類世世代代的共同奮斗。現在是從傳統增長到可持續發展的轉變時期，因而最近幾代人的努力是成功的關鍵。