Huge ice sheets, several thousand meters thick, encased parts of North America, Asia, and Europe.

巨大的冰層有數千公尺厚，覆蓋部分北美洲、亞洲與歐洲，

We commonly know it as the "Ice Age."

這就是廣為人知的「冰河時期」，

But geologists call it the Last Glacial Maximum.

但地質學家通常稱之「末次冰盛期」，

That's because it's the most recent time that ice reached such a huge extent, and “ice age” is an informal term without a single agreed-upon definition.

因為那是最近一次被如此大規模冰層覆蓋，而「冰河時期」是非正式的說法，在定義上意見尚未統一。

Over the last million years, there have actually been about 10 different glacial maxima.

過去 100 萬年之間，實際上發生過 10 次不同規模的冰盛期。

Throughout Earth's history, climate has varied greatly.

綜觀地球歷史，氣候經歷相當大的變化，

For hundreds of millions of years, the planet had no polar ice caps.

數億年來的氣候變遷，地球的極地冰冠消失，

Without this ice, the sea level was 70 meters higher.

沒有了冰層，海平面會上升 70 公尺。

At the other extreme, about 700 million years ago, Earth became almost entirely covered in ice, during an event known as “Snowball Earth.”

另一次極端現象，大概 7 億年前，地球幾乎完全被冰層覆蓋，這個事件被稱為「雪球地球」。

So what causes these massive swings in the planet's climate?

所以，是什麼原因導致地球的氣候變動如此劇烈？

One of the main drivers is atmospheric carbon dioxide, a greenhouse gas that traps heat.

其中一個主要的驅動因子是大氣中的二氧化碳，一種能保留熱能的溫室氣體，

Natural processes, such as volcanism, chemical weathering of rocks, and the burial of organic matter,

自然過程，像火山作用、岩石的化學風化作用，以及被掩埋的有機質，

can cause huge changes in carbon dioxide when they continue for millions of years.

持續數百萬年的作用，就能造成二氧化碳含量巨大改變。

Over the past million years, carbon dioxide has been relatively low, and repeated glacial maxima have been caused by cycles in Earth's movement around the sun.

過去 100 萬年間，二氧化碳含量相較之下處於低點，而反覆的冰盛期是因為地球繞著太陽公轉的週期造成。

As Earth rotates, it wobbles on its axis and its tilt changes, altering the amount of sunlight that strikes different parts of its surface.

當地球公轉時，地軸方向逐漸漂移，傾斜角度改變，改變地球表面不同地區接收到的陽光照射量。

These wobbles, combined with the planet's elliptical orbit, cause summer temperatures to vary depending on whether the summer solstice happens when Earth is closer or farther from the sun.

這樣的晃動，加上地球公轉的橢圓形軌道，造成夏天溫度的差異，取決於當地球離太陽更近一點或更遠一點時，夏至有沒有發生，

Approximately every 100,000 years, these factors align to create dramatically colder conditions that last for millennia.

大約每 10 萬年，這些因素會結合在一起，造成長達上千年之久的嚴寒氣候。

Cool summers that aren't warm enough to melt the preceding winter's snow allow ice to accumulate year after year.

涼爽的夏天不夠溫暖，導致先前冬天的積雪無法融化，使冰雪年復一年堆積，

These ice sheets produce additional cooling by reflecting more solar energy back into space.

這些冰層會反射更多太陽能量回太空，造成更寒冷的環境，

Simultaneously, cooler conditions transfer carbon dioxide from the atmosphere into the ocean, causing even more cooling and glacier expansion.

同時，寒冷的環境將二氧化碳從大氣轉移至海洋中，造成更多冷卻作用，還有冰河擴張。

About 20,000 years ago, these trends reversed when changes in Earth's orbit increased summer sunshine over the giant ice sheets, and they began to melt.

大約 2 萬年前，這樣的情勢反轉了，當地球運行軌道改變，增加夏天照射，在冰層上的陽光，使得冰層開始融化。

The sea level rose 130 meters and carbon dioxide was released from the ocean back into the atmosphere.

海平面上升了 130 公尺，二氧化碳也從海洋釋放到大氣中。

By analyzing pollen and marine fossils, geologists can tell that temperatures peaked about 6,000 years ago, before another shift in Earth's orbit caused renewed cooling.

透過花粉跟海洋化石的分析，地質學家得知溫度在 6 千年前達到高峰，之後地球軌道再次轉變，冷卻作用又再次開始。

So what's coming next?

所以接下來會發生什麼事？

Based on the repeated natural cycle seen in the climate record, we'd normally expect the Earth to continue a trend of gradual cooling for the next few thousand years.

根據氣候記錄中重覆發生的自然週期，正常來說我們會預期地球在接下來數千年間，會有漸漸冷卻的趨勢，

However, this cooling abruptly reversed about 150 years ago.

然而，大約 150 年前，這樣的冷卻作用卻突然被翻轉了。

Why?

為什麼？

Carbon dioxide levels in the atmosphere have been rising since the 19th century, when fossil fuel use increased.

從 19 世紀以來，大氣中的二氧化碳含量上升，因為石化燃料使用量增加。

We know that from studying air bubbles trapped in Antarctic ice.

我們透過研究南極冰層中的氣泡得知這個現象。

This surge in carbon dioxide also coincides with a global temperature increase of nearly one degree Celsius.

二氧化碳含量高漲也正好與全球溫度上升將近攝氏 1 度的情況重合。

Ice cores and atmospheric monitoring stations show us that carbon dioxide levels are rising faster, and to higher levels, than at any point in the last 800,000 years.

冰核與大氣監控站顯示二氧化碳含量上升相當快速，並且比過去 80 萬年間任何時間點都要高。

Computer models forecast another one to four degrees Celsius of warming by 2100, depending on how much additional fossil fuel we burn.

電腦模型預測到西元 2010 年為止，地球會再上升攝氏 1 到 4 度，根據我們又再燃燒了多少石化燃料。

What does that mean for the ice currently on Greenland and Antarctica?

對目前格陵蘭嶼南極大陸的冰層來說，又代表了什麼？

Past climate changes suggest that even a small warming shift can begin a process of ice melt that continues for thousands of years.

過去的氣候變遷顯示即使是微小的暖化轉變都可能造成持續數千年的融冰過程。

By the end of this century, ice melt is expected to raise the sea level by 30 to 100 centimeters, enough to impact many coastal cities and island nations.

到這世紀末時，融化的冰層預期會提升海平面 30 到 100 公分，足以影響許多沿海城市與島國。

If a four-degree Celsius warming persisted for several millennia, the sea level could rise by as much as 10 meters.

如果攝氏 4 度的暖化程度持續數千年，海平面將會上升 10 公尺。

By studying past climates, scientists learn more about what drives the shifts in ice that have shaped our planet for millions of years.

透過研究過去的氣候，科學家更了解是什麼原因造成冰層轉變，如此的轉變在數百萬年間不斷形塑我們的地球。

Research suggests that by taking action now to reduce carbon dioxide emissions quickly, we still have the opportunity to curb ice loss and save our coastal communities.

研究顯示現在採取行動，盡快減少二氧化碳排放，我們仍有機會抑制冰層流失，並拯救我們的沿岸社區。

If your'e a student watching this now, we have a question for you.

如果你是一名學生正在觀看這隻影片，我們有個問題要問你。

Do you ever feel like you're too young to have any real impact on climate change?

你是否覺得自己還太年輕，無法對氣候變化產生任何實際的影響？

If so, we disagree.

如果是的話，我們不同意你這個觀點。

All these students in our Ted-Ed clubs program are speaking up and taking action to fight for a healthy, habitable planet.

在我們的 Ted-Ed 俱樂部中，所有這些學生都在發聲，為健康、宜居的星球而採取行動。

And maybe the next great idea or well-chosen word will change the world or change someone's mind will be yours.

也許下一個提供好主意或精闢的想法改變世界或改變某人的想法的會是你。