Those are what we study.

這些正是我們研究的。

This is a piece of ice – about 20,000 years old – from Antarctica.

這是一片來自南極的冰，有大約 2 萬年的歷史。

And bubbles trap air from 20,000 years ago, so we can find out what air was like back then.

泡泡困住了 2 萬年前的空氣，所以我們可以得知當時的空氣狀況。

(We) Can figure out if carbon dioxide has gone up or down.

我們可以得知二氧化碳濃度是否上升或是下降。

And what we've learned from that is carbon dioxide is higher now than it's been for at least the last million years, probably the last 20 million years, but that's less certain.

得出的結果是目前二氧化碳濃度達到過去 100 萬年來的最高峰，或許是過去 2000 萬年，不過後者比較不確定。

So it's really quite a dramatic thing that we humans have done to the carbon dioxide.

我們人類對二氧化碳帶來了劇烈影響。

Hey smart people.

聰明人大家好。

Joe here.

我是 Joe。

Earth's atmosphere and climate have changed in a big way, and they are continuing to change.

地球的大氣與氣候今非昔比，而且還在持續變化。

There's no doubt about that, and we've known it for decades.

這一點毋庸置疑，我們幾十年前就知道了。

But Earth's climate has always changed throughout its history.

不過地球的氣候隨時都在變化。

So how do we know this time is different?

我們怎麼知道現在特別不同？

We know because at places like the Scripps Institution of Oceanography in southern California, we have freezers full of ancient ice that let us look into the past, thousands.

我們之所以知道，是因為在加州南部的斯克里普斯海洋研究所，有承載上千年歷史的古老冰塊。

Even millions of years, and measure exactly what Earth's atmosphere, and its climate, were like throughout deep history.

甚至達百萬年，能夠用來測出地球大氣及氣候於過往歷史的變化。

I recently stopped by to visit Dr. Jeffrey Severinghaus, who studies ice cores.

我近期前往拜訪 Jeffrey Severinghaus 博士，他專門研究冰塊。

He's part of a team working to find the oldest ice on Earth.

他們小組致力於發掘地球上最古老的冰。

Each of these little blocks of frozen water can tell us something about our planet's past, long before we existed – and where it's heading, now that we do.

這些小小結冰體能告訴我們地球的過去，早在我們存在以前 —— 並且估算未來的動向。

And inside these tiny bubbles in this ice are old bubbles of air that existed on this planet as old as that ice is.

冰塊裡的這些微小氣泡，蘊藏著和冰塊本身一樣古老的氣體。

Yeah.

沒錯。

That's the atmosphere of the planet, trapped in those little bubbles.

這些是地球的大氣，被困在了小氣泡裡。

What happens in the polar regions is it's too cold to melt.

極地地區實在太冷了，雪不會融化。

So when snow falls it doesn't melt, it just piles up and piles up, and eventually turns into ice under its own weight.

所以當雪落下、一層一層堆積後，被自己的重量壓成冰。

But if you think about what snow is like, if you have a snowflake you have air in between the snowflake.

想像一下雪長什麼樣，雪花之間其實有氣體。

As snow becomes more and more dense, it tends to squeeze out the air between snowflakes, but it turns out it doesn't squeeze out all the air.

當雪壓得越來越緊密，雪花之間的氣體就會被擠壓，不過並非所有氣體都會被擠出。

As more layers of snow fall and condense, those tiny voids are literally frozen in time, layer upon layer.

隨著越來越多層的雪堆積、壓實，這些小小的空隙就被凍住了，一層接著一層。

And, there are a lot of layers.

而且是真的非常多層。

Some ice cores have annual layers just like trees do, you know how you can count tree rings?

有些冰核和樹一樣有年層，你知道怎麼數樹的年輪嗎？

So some graduate student sits there and counts 50,000 annual layers.

有研究生坐在那裡數，數出超過 5 萬個年層。

Of course it has to be a graduate student!

可想而知是研究生做的！

What a lot of work.

耗功夫啊。

But to study ancient ice, first you have to find ancient ice.

不過為了研究古老冰塊，首先必須找到它們。

Where are you doing this research?

你在哪裡做這項研究？

Where are you collecting these ice cores?

在哪裡收集這些冰核的？

This is from a place called Taylor Glacier in Antarctica.

這塊來自南極的泰勒冰川。

Taylor Glacier is a 54 kilometer stretch of ice and rock.

泰勒冰川長達 54 公里，含冰和石塊。

People like Dr. Severinghaus can read it like a book–full of stories about our ancient climate.

如 Severinghaus 博士這些人，能夠從它讀出許多有關古代氣候的故事。

Taylor Glacier is special because it's one of the few places on Earth where the ancient ice has risen to the surface.

泰勒冰川很特別，因為它是地球上少數古老冰塊浮至表層的地方。

So, you only have to drill 5-10 meters to get the ice.

所以只需要往下鑽個 5 到 10 公尺就能取得冰塊。

Which is much easier than drilling a deep ice core which is 3,000 meters and costs 50 million dollars.

比起耗資 5000 萬、鑽 3000 公尺取得深層冰核，這簡單很多。

It's basically a cylinder that has little tiny teeth on the bottom.

基本上就是底部有小鋸齒的圓筒。

And when you rotate the barrel it carves out the ice on the edges and leaves behind an ice core in the middle.

轉動圓筒時，它會沿著邊緣切出冰塊，留下一條冰核。

Once the core is pulled up, it's packed up and sent off, carrying a slice of history inside it.

冰核一旦被取出，就會被包裝然後運送，連同帶上一小段歷史。

It's a slow process, it takes like a month for the ship to get here.

過程很緩慢，要花上一個月才能送到。

Whether you're standing in the middle of the Amazon rainforest or at the North Pole, you're breathing roughly the same air.

不論你是站在亞馬遜雨林的中央還是北極，你呼吸的空氣基本上都一樣。

Our atmosphere is pretty much the same everywhere.

各地的大氣基本上一致。

Which means that a tiny air bubble from that one spot is enough to paint a picture of what the entire planet's atmosphere looked like so many years ago.

意思是來自那個地方的小氣泡已足以描繪許多年前整個地球的大氣狀況。

This is the freezer.

這是冰庫。

We won't be in there long, so don't worry about the cold.

我們不會在裡面待太久，你不用擔心溫度。

So this is what a typical ice core sample looks like.

冰核樣本基本上就長這樣。

Now you'll notice that there's no bubbles.

注意現在裡頭並沒有氣泡。

That's because when you get down below 600-700 meters, the pressure is so high that the air turns into something called a clathrate which is an ice-like substance.

那是因為到達地下六七百公尺時，壓力高到空氣轉變為一種稱為晶籠化合物的東西，看起來就像冰。

Clathrates are crystals, where instead of bubbles, the molecules are trapped in a cage made by the bonds between frozen water molecules.

晶籠化合物是晶體，氣泡分子被困在凍結的水分子之間。

There's still gas in there.

這裡頭還有氣體。

There's still gas molecules but they're not in a gas phase.

裡頭依然有氣體分子，不過不是氣體的形態。

Man the patterns are so cool, you must randomly see such cool ice phenomena.

天啊紋路看起來好酷，你一定有事沒事就會看到那麼酷的冰塊現象。

It's cold in here!

這裡頭很冷！

This cold!

這麼冷！

Funny how that works.

溫度計竟然還能運作。

Okay, but how do you get the ancient air out of the ice to measure it?

不過究竟要如何把古老空氣從冰塊裡取出然後測量？

I mean, without contaminating it with… all this air around us?

我的意思是，它怎麼樣才不會被我們周圍的空氣污染？

So this is how we actually extract the ancient air, if you will.

要做的話，這是我們萃取古代空氣的方法。

We take a piece of ice and put it in a vacuum flask, and pump out all of the modern air, the air we're breathing right now, using a vacuum line.

我們取一小塊冰，把它放進這個燒瓶，然後用真空管把所有現代空氣吸出，就是我們現在在呼吸的。

This is a vacuum pump here.

這是一個真空幫浦。

So we make a seal, we pump all the modern air, and close this valve, and then you only have an ice cube and a little bit of water vapor, but no air.

密封之後抽出所有現代空氣，將氣閥關緊，這樣燒瓶裡就只有冰塊和一點水蒸氣，沒有空氣。

Then we melt the ice, and the melting of the ice releases those little air bubbles of ancient air.

然後我們將冰塊融掉，融化時冰塊裡頭的小氣泡會釋出古代空氣。

So because you already let out the "now air," the only gasses that are coming out are the ones that are trapped inside the ice.

因為你已經把所有現代空氣吸出了，裡面唯一會有的空氣就只有原先被困在冰塊裡的那些。

Right, and then once we've done that, we can purify the gas a little bit by freezing the water.

沒錯，一旦完成這步驟，我們可以藉由冷凍水加強淨化氣體。

So they pump out all the modern air, melt the ice to let the ancient atmosphere vaporize, re-freeze the water, and pump that ancient atmosphere out so it can be measured.

所以他們吸出現代空氣、將冰塊融掉、讓古代氣體蒸發，重新凍結水，然後將古代氣體抽出、測量。

This is a liquid helium tank, it's cold enough - it's at 4 kelvin, 4 degrees about absolute zero.

這是一桶液態氦，溫度夠冷，差不多凱爾文 4 度，絕對零度 (−273 °C) 周圍 4 度。

It's cold enough that all the air actually condenses and turns into ice - air ice.

冷到空氣會壓縮、轉變成冰塊，氣冰。

Every gas, will freeze.

所有氣體都會凍結。

Every gas except helium.

所有氣體，除了氦氣。

So then we take it over here.

然後我們把它拿來這。

This is the analysis part of it.

這裡是進行分析的地方。

This tube is actually a bottle, a long skinny bottle that's capable of dipping itself into the liquid helium.

這條管子其實是一個瓶子，一個非常細的瓶子，細到足以拿來浸到液態氦裡。

You wouldn't want to be getting your own hands too close to 4 kelvin.

你不會想拿自己的手伸進絕對零度的環境裡。

No.

絕不。

The frozen air gets put into this, a mass spectrometer, which basically measures the masses of really tiny things.

冷凍的氣體被放進這台巨大的分光計，基本上就是用來測量非常微小的東西的質量。

We measure the chemical composition of the atmosphere using isotopes: they're like different flavors of atomic elements.

我們利用同位素測量大氣中的化學成分：就好像不同口味的原子元素。

Isotopes, those flavors of elements, have unique masses, and the mixture of them in the air bubbles can tell us all kinds of things about ancient earth.

同位素，這些多種口味的元素，有各自獨特的質量，他們在氣泡中的各種混合能夠告訴我們關於古代地球的所有事。

We use the isotopes of nitrogen to tell ancient temperature at the time the snow was falling.

我們利用氮同位素辨別雪落下當時的古代氣溫。

Ordinary nitrogen has a mass of 14, but the rare isotope nitrogen 15 has a mass of 15.

一般的氮質量 14，不過罕見的同位素氮 15 的質量為 15。

It turns out that relative proportions of N15 and N14 are sensitive to temperature.

氮 15 和氮 14 的相對比例對氣溫很敏感。

So, whatever the temperature is at a particular time, it's creating different mixes of different flavors of gasses in the atmosphere, like a fingerprint for temperature.

所以特定時間下的氣溫會製造出不同的大氣氣體組成，就好像氣溫的指紋。

That's right, and that's trapped in air bubbles for posterity.

沒錯，而且被困在氣體裡供我們後代研究。

So the sample here starts out waiting its turn and when its turn comes the valve opens and goes into this little tiny tube, which leads into the mass spectrometer, here.

所以這邊的樣本在排隊，輪到它們的時候氣閥打開、把他們送進這個小管子，然後到這個質量分光計裡。

And it gets accelerated by a 3,000 volt electrical gradient, which makes the ions go really fast.

它以 3000 伏特電子升降率加速，使得離子行進得非常快。

And then they hit this magnet and they're forced to make a 90-degree right turn.

然後它們會撞到這塊磁鐵，被迫在這裡轉 90 度。

And in doing so, heavy things like N15 try to go straight, and lighter things like N14 get bent more.

如此一來，如氮 15 之類的重質量承恩會走直線，比較輕的如氮 14 就會彎比較大。

It's like being in a car.

就好像開車一樣。

You can't turn as fast in a big heavy car.

太重的車無法快速轉彎。

So they swing out, and then the detector is seeing what swung out farther.

會擺出去，然後偵測器偵測出哪一個擺幅比較大。

So, you're getting resolution of things that differ by a single neutron when they're flying through that curve?

所以你藉由單一種中子的飛行擺幅大小獲得分析結果？

That's pretty cool.

真是酷斃了。

The same idea can be used to find out more than just temperature.

同一種方式不只能拿來發掘溫度。

Labs all over the world use elements trapped in air, trapped in ice cores, to paint a map from our distant past to today.

世界各地的實驗室利用空氣中、冰核中的元素描繪遠古至今的形貌。

Oxygen isotopes can tell us how oceans changed, mineral dust tells us about how the atmosphere moved around, there are chemical clues about early volcanoes.

氧同位素能夠告訴我們海洋的變化，礦物塵埃告訴我們大氣移動的途徑，每一座火山都有化學線索。

But maybe most importantly, we can trace changing levels of carbon dioxide.

不過或許最重要的是，我們能夠回溯二氧化碳的濃度。

So the climate has changed before, how do we know that this time it's us.

從前也曾發生氣候變遷，怎麼知道這次是我們造成的。

The way we know, is just like we talked about with nitrogen, the carbon in carbon dioxide also has two flavors.

我們得知的方法就和氮氣一樣，二氧化碳中的碳也有兩種口味。

There's carbon 12, which is ordinary carbon, and then a very rare form of carbon, carbon 13.

有碳 12，是一般的碳，還有非常罕見的碳，叫做碳 13。

So, that's how we know it's human caused.

我們因此得知是人為造成的。

The atmosphere, as it goes up in CO2 concentration, the carbon 13 of the atmosphere is taking a nosedive.

大氣中的二氧化碳濃度升高時，大氣中的碳 13 卻急劇下降。

And that's not what would happen if it was natural CO2.

如果是自然的二氧化碳，就不會發生這種事情。

Because fossil fuel CO2 is very depleted in carbon 13.

因為化石燃料中的二氧化碳的碳 13 衰減得非常迅速。

This comes from the fact that plants prefer to eat CO2 made of carbon-12.

這是因為植物比較喜歡吃由碳 12 組成的二氧化碳。

And when we burn fossil fuels made from those ancient plants, the fraction of carbon-12 in the atmosphere goes up while carbon-13 goes down.

當我們燃燒古代植物組成的化石燃料，大氣中的碳 12 就會上升，碳 13 則會下降。

We've only been measuring carbon dioxide in the atmosphere since 1957, but using the data from ice cores, we can trace levels back way farther.

我們從 1957 年才開始測量大氣中的二氧化碳，不過藉由取自冰核的資料，我們能追溯到更久遠之前的數值。

And this is what we see: CO2 was pretty flat for most of the past 1,000 years.

以下是結果：過去 1000 年以來，二氧化碳濃度基本上都很穩定。

All around 280 ppm.

均為 280ppm 左右。

Now we're going to add in the carbon 13 abundance, this gold line.

現在加入碳 13 的豐度數值，也就是這一條黃線。

And you can see that was also pretty constant for most of the last thousand years.

如你所見，過去 1000 年來它的濃度也很穩定。

But then around 1850, right when carbon dioxide concentration started to rise, the carbon 13 abundance started taking a nosedive.

不過在 1850 年左右，二氧化碳濃度開始增加，碳 13 的豐度開始急劇下降。

And this kind of unambiguously tells you that humans did it.

這點明顯顯示為人為所致。

That's why I call it the smoking gun of human causation.

我稱之為「人為的確切證據」。

There are lots of other ways we know, but this is the simplest.

還有其他方式可以得出這個結果，不過這是最簡明的方式。

We're moving into uncharted territory.

我們正要進入一個未知的領域。

The last time something like this shows up in the ice record is around 55 million years ago, when a volcano popped up under an oil field and cooked basically everything.

上一次出現這種數據是大約 5500 萬年前，一座油田底下的火山噴發，燒毀了幾乎一切。

It sent all the carbon dioxide into the atmosphere.

它將所有的二氧化碳釋放至大氣。

So, the carbon dioxide shot up, we think it nearly quadrupled, and the climate warmed by 6 degrees.

所以二氧化碳濃度飆升，推估達到近 4 倍，氣候暖化了 6 度。

The most important thing is right away to solve this global warming problem.

當務之急是解決全球暖化問題。

We don't have much time left.

我們沒剩多少時間了。

We got to put aside all of our political differences.

必須將所有政治問題放到一旁。

We can do this, I know we can.

我們做得到的，我知道我們可以。

We can. But will we?

我們可以。但我們會嗎？

I hope so. Stay curious.

希望如此。永保好奇。