氣象學在託福聽力科技類文章常出現的主題，而且往往國內學生在這方面的託福聽力背景知識知之甚少，今天我們就讓大家感受一下托福考試中的氣象知識。
比如有一篇難度頗大的文章，提到了全球氣候在冰期和暖期間的切換。
Now, the typical pattern for an interglacial period, and we have studied several, is that the concentration of carbon dioxide and methane gas actually reaches it... its peak, that is, there is the most carbon dioxide and methane gas, uh, greenhouse gases in the atmosphere just after the beginning of the interglacial period. And then, for reasons which are not entirely clear, the concentration of greenhouse gases gradually goes down. Now, the climate continues to warm for a while because there is a lag effect. But uh, gradually as the concentration of greenhouse gases goes down, earth starts to cool again, and eventually you slip back into an Ice Age.
原來這大氣中溫室氣體(主要是二氧化碳和甲烷)有關，當溫室氣體含量下降，溫度就下降，慢慢的地球就進入了冰期。之後，因爲某些尚不明確的'原因，溫室氣體的含量有開始回升，地球又逐漸變暖。這就是地球在冰期和暖期切換的原因。
In fact, back in the 1970s, a lot of theorists were predicting that, you know, the climate would start to cool and we’d slowly enter into the new Ice Age. And then they were puzzled as to why it didn’t seem to be happening.
但是人類的活動正在改變這一循環，事實上，有一批科學家根據規律推測地球即將進入下一個冰期，但是這個冰期至今還沒有到來。現在我們已經知道，這是因爲人類排放了太多的二氧化碳到了大氣中。
那未來究竟會怎樣呢?教授是這樣說的：
Now, what are the implications for the future? Well, um... it is a little tricky. I mean, you could say, well, here is an example of ... um ... human activity, the agricultural revolution which actually was beneficial; we altered the climate for the better, perhaps, by preventing an Ice Age. But then industrialization, of course, has drastically increased the amount of carbon dioxide that humans are putting into the atmosphere, the burning of fossil fuels tends to put a lot of CO2 into the atmosphere. Um... so we are entering into uncharted territory now, in terms of the amount of carbon dioxide, the concentrations of carbon dioxide that are now being put into the atmosphere as a result of industrialization and the use of fossil fuels.
目前的研究也沒有得出明確的結論。好的方面是我們避開了一次本該到來的冰期。但是另一方面來看，人類燃燒化石能源，排放大量的二氧化碳有讓地球的氣候開始了史無前例的變化，使我們進入了未知的領域。
那未來究竟會怎樣呢，後天電影中告訴我們地球可能很快進入冰期，迎來大冰凍，事實上，這個觀點還是有一定科學依據的，這一事件在歷史上發生過三次，最近的一次稱爲“新仙女木事件(Younger Dryas)”
The Younger Dryas, from c. 12,900 to c. 11,700 years ago (BP), was a sharp decline in temperature over most of the northern hemisphere, at the end of the Pleistocene epoch, immediately preceding the current warmer Holocene. It was the most recent and longest of several interruptions to the gradual warming of the Earth's climate since the severe Last Glacial Maximum, c. 27,000 to 24,000 BP. The change was relatively sudden, taking place in decades, and resulted in a decline of 2 to 6 degrees Celsius, advances of glaciers and drier conditions, over much the temperate northern hemisphere. It is thought to have been caused by a decline in the strength of the Atlantic meridional overturning circulation, which transports warm water from the equator towards the North Pole, and which in turn is thought to have been caused by an influx of fresh cold water from North America into the Atlantic. The Younger Dryas was a period of climatic change, but the effects were complex and variable. In the southern hemisphere, and some areas of the north such as the south-eastern United States, there was a slight warming.
上次冰期結束時，大約1.7萬年前地球開始變暖，氣溫逐漸地回升。兩極、北美和北歐的冰川開始消融，海平面逐漸上升，渤海、黃海、挪威海的草原被水淹沒。到了1.3萬年前，北美和北歐的冰雪已經融化了相當大一部分，南北半球春暖花開，一片繁榮景象。但就在此時北美巨大的冰川融化，和現在北極冰蓋的融化相似，巨量的淡水衝入北大西洋，導致北大西洋暖流中斷，在短短十年內，地球平均氣溫下降了大約7、8℃。這次降溫持續了上千年，直到11500年前，氣溫才又突然回升。
