When will the next ice age happen? - Lorraine Lisiecki

譯者: Lilian Chiu 審譯者: congmei Han

Twenty thousand years ago,

兩萬年前，

the Earth was a frigid landscape where woolly mammoths roamed.

地球上是嚴寒的地景， 長毛象漫遊的地方。

Huge ice sheets, several thousand meters thick,

大冰原有數千公尺的厚度，

encased parts of North America, Asia, and Europe.

覆蓋了北美洲的一部分， 亞洲，及歐洲。

We commonly know it as the "Ice Age."

那就是我們一般所知的 「冰河時期」。

But geologists call it the Last Glacial Maximum.

但地質學家叫它「末次冰盛期」。

That’s because it’s the most recent time that ice reached such a huge extent,

因為這是最近期一次 冰的範圍達到這麼大，

and “ice age” is an informal term without a single agreed-upon definition.

而「冰河時期」是非正式的用語， 沒有意見一致的定義。

Over the last million years,

在過去的一百年間，

there have actually been about 10 different glacial maxima.

已經有大約十次不同的冰盛期。

Throughout Earth’s history, climate has varied greatly.

在地球的整個歷史上， 氣候經歷過很大變化。

For hundreds of millions of years,

數億年來隨著氣候變化，

the planet had no polar ice caps.

地球沒有了極地冰冠。

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

沒有這層冰，海平面 就高了 70 公尺。

At the other extreme, about 700 million years ago,

另一次極端現象發生在 大約七億年前，

Earth became almost entirely covered in ice

地球幾乎完全被冰覆蓋，

during an event known as “Snowball Earth.”

這個事件叫做「雪球地球」。

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

地球氣候的變動這麼巨大， 是什麼原因造成的？

One of the main drivers is atmospheric carbon dioxide,

主要的驅動因子之一， 是大氣中的二氧化碳，

a greenhouse gas that traps heat.

這種溫室氣體會把熱給困住。

Natural processes, such as volcanism,

自然過程，如火山作用、

chemical weathering of rocks,

石頭的化學風化，

and the burial of organic matter,

以及有機物質被掩埋，

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

如果這些過程持續數百萬年， 就能造成二氧化碳含量的巨大改變。

Over the past million years, carbon dioxide has been relatively low,

在過去一百萬年間， 二氧化碳含量算是相對比較低，

and repeated glacial maxima

而重覆的冰盛期

have been caused by cycles in Earth’s movement around the sun.

是因為地球繞著太陽 公轉的循環所造成。

As Earth rotates,

地球轉動時會隨著地軸晃動，

it wobbles on its axis and its tilt changes,

傾斜度就會改變，

altering the amount of sunlight that strikes different parts of its surface.

改變地球表面不同部分 所接收到的陽光量。

These wobbles, combined with the planet’s elliptical orbit,

這些晃動加上地球的橢圓軌道，

cause summer temperatures to vary

就會造成夏天溫度改變，

depending on whether the summer solstice happens when Earth is closer

取決於當地球離太陽更近或更遠時

or farther from the sun.

是否發生夏至。

Approximately every 100,000 years,

大約每十萬年，

these factors align to create dramatically colder conditions that last for millennia.

這些因子就會匹配在一起， 造成持續百年非常寒冷的環境。

Cool summers that aren’t warm enough to melt the preceding winter’s snow

涼爽的夏季不夠溫暖， 無法使先前冬季的積雪融化，

allow ice to accumulate year after year.

讓冰一年又一年累積下去。

These ice sheets produce additional cooling

這些冰原會產生額外的冷卻，

by reflecting more solar energy back into space.

過程就是它們會把更多的 太陽能反射回太空。

Simultaneously, cooler conditions transfer carbon dioxide

同時，更涼爽的環境會把二氧化碳

from the atmosphere into the ocean,

從大氣轉移到海洋中，

causing even more cooling and glacier expansion.

造成更多的冷卻作用 以及冰河擴張。

About 20,000 years ago,

大約兩萬年前，

these trends reversed when changes in Earth’s orbit increased summer sunshine

這些趨勢被反轉了，當時 地球軌道的改變增加了夏天

照射在大冰原上的陽光， 導致大冰原開始融化。

over the giant ice sheets, and they began to melt.

The sea level rose 130 meters

海平面上升了 130 公尺

and carbon dioxide was released from the ocean back into the atmosphere.

二氧化碳從海洋釋放出來， 回到大氣當中。

By analyzing pollen and marine fossils,

透過分析花粉和海洋化石，

geologists can tell that temperatures peaked about 6,000 years ago,

地質學家得知，溫度在 約六千年前達到高峰，

before another shift in Earth’s orbit caused renewed cooling.

之後地球軌道又發生一次轉變， 讓冷卻作用再次開始。

So what’s coming next?

所以，接下來會發生什麼？

Based on the repeated natural cycle seen in the climate record,

根據氣候記錄中可以看見的 重覆性自然循環，

we’d normally expect the Earth to continue a trend of gradual cooling

正常來說，我們會預期地球 漸漸冷卻的趨勢會持續下去，

for the next few thousand years.

在接下來幾千年都會持續。

However, this cooling abruptly reversed about 150 years ago.

然而，大約在 150 年前， 這個冷卻作用突然反轉了。

Why?

為什麼？

Carbon dioxide levels in the atmosphere have been rising since the 19th century,

大氣中的二氧化碳含量 從 19 世紀就開始升高，

when fossil fuel use increased.

原因是化石燃料的使用增加。

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

我們是透過研究被困在南極冰中的 氣泡得知這個事實的。

This surge in carbon dioxide also coincides

二氧化碳高漲的同時，

with a global temperature increase of nearly one degree Celsius.

剛好也發生了全球溫度 上升接近攝氏一度。

Ice cores and atmospheric monitoring stations

冰核和大氣監控站

show us that carbon dioxide levels are rising faster,

發現二氧化碳含量快速上升，

and to higher levels,

所達到的含量比過去

than at any point in the last 800,000 years.

80 萬年間任何時點的含量都高。

Computer models forecast another one to four degrees Celsius of warming by 2100,

電腦模型預測，到 2100 年 會再上升攝氏一至四度。

depending on how much additional fossil fuel we burn.

預測的依據是我們燃燒掉的 額外化石燃料量。

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

對於目前在格陵蘭和南極的 冰來說，那有什麼意涵？

Past climate changes suggest that even a small warming shift

過去的氣候改變，顯示出 即使只有小小的暖化轉變，

can begin a process of ice melt that continues for thousands of years.

也會引起一個持續 數千年的融冰過程。

By the end of this century,

到這個世紀末，

ice melt is expected to raise the sea level by 30 to 100 centimeters,

預期融冰會造成海平面 上升 30 到 100 公分，

enough to impact many coastal cities and island nations.

足以影響到許多 沿岸城市和島嶼國家。

If a four-degree Celsius warming persisted for several millennia,

如果四度的暖化持續數百年，

the sea level could rise by as much as 10 meters.

海平面可能會 提升 10 公尺之多。

By studying past climates,

藉由研究過去的氣候，

scientists learn more about what drives the shifts in ice

科學家得以更了解 是什麼造成冰的轉變

that have shaped our planet for millions of years.

正是這種轉變 形塑出數百年間的地球。

Research suggests that by taking action now

研究指出，如果現在就採取行動，

to reduce carbon dioxide emissions quickly,

盡快減少二氧化碳排放，

we still have the opportunity to curb ice loss and save our coastal communities.

我們就還有機會遏止冰的流失， 拯救我們的海岸社區。