Narrator: Listen to part of a lecture in an environmental science class.

旁白：下面请听一段环境科学讲座的片段。

Professor: Now, over the next few weeks, we're gonna focus on carbon and its role in what's known as the "greenhouse effect".

教授：接下来的几周，我们将集中在碳元素上以及它在“温室效应”中的作用。

Everyone knows what that is, right?

大家都知道温室效应是什么，对吗？

But let's make sure anyway.

我们还是来确认下。

Yes, Karlie?

Karlie？

Student: The greenhouse effect is when gases in Earth's atmosphere act like the glass in a greenhouse or a hothouse.

学生：温室效应是当温室气体在地球大气层里，它们就像温室的玻璃一样。

They trap in heat which warms up the earth.

不让热量消散，使得地球温度上升。

Professor: Gases like?

教授：气体比如是？

Student: Um, water vapor? Carbon dioxide?

学生：水蒸气？二氧化碳？

Professor: Right. Carbon dioxide.

教授：对的。二氧化碳。

We hear a lot about carbon these days, no?

我们最近听说很多有关碳的事，不是么？

Carbon emissions, carbon burning, leaving a carbon footprint.

碳排放，碳燃烧，碳足迹。

So it'd be easy to assume that any form of carbon burning is necessarily a bad thing.

所以我们很容易推断出任何形式的碳燃烧必定是个坏事。

But the fact is: it's not quite that simple.

但是事实是：并不是那么简单。

So we're gonna focus today on the difference between good, bad, and well, the, not so bad, the potentially okay carbon burning.

所以今天我们主要来看下那些好的，坏的，不是那么坏的，潜在是有益的碳燃烧的区别。

OK. Good carbon burning.

ok。好的碳燃烧。

Well, we all have a personal stake in this because burning carbon is the basis of life.

我们每个人都亲自参与其中，因为燃烧碳是生命的基础。

We wouldn't be here if we ourselves weren't burning carbon.

如果我们不燃烧碳那么人类就不会存在。

Basically, all living things burn carbon to survive.

基本上，所有的生物都依赖燃烧碳而存活。

Usually this happens at the cellular level and what's burned is carbon in the form of sugars, glucose.

通常这是发生在生物的细胞阶段，燃烧的是以糖，葡萄糖为形式的碳。

Oxygen gets chemically combined with sugars in our cells and the energy produced from that reaction is then used to power the cells.

在我们细胞中，氧通过化学反应与糖结合，化学反应产生能量来供给细胞。

So just by breathing you could say we are all guilty of carbon emission and contribute to the amount of carbon in the atmosphere.

所以仅仅呼吸一次，你可以说我们都是碳排放的“罪人”，增加了大气中的碳含量。

Student: Um, another thing about atmospheric carbon: it keeps us from freezing.

有关大气中的碳的另一件事是：它让我们远离寒冷。

Because without carbon and other greenhouse gases, our planet would be the same temperature as outer space, around four degrees above absolute zero.

因为没有碳和其他温室气体，我们星球上的温度跟外太空是一样的，大概零上四度。

And there's nothing going on at that temperature.

这个温度上什么都没有。

No possibility of life of any sort.

不可能有任何形式的生命体。

So without atmospheric carbon, life couldn't exist on Earth.

所以没有大气中的碳，地球上不会有生命。

Now, another thing to remember is that carbon is always being removed from the atmosphere.

现在，还要记住另一件事，就是碳是总是从大气中清除掉。

It gets used up.

它被消耗了。

Largely it’s consumed by plant life through photosynthesis.

大部分是被植物通过光合作用消耗掉。

Also, it dissolves in the oceans or gets stored deep in the ocean.

而且它会溶解在海里或储藏在海底。

You have shellfish that use the CO2 dissolved in the water to make carbonate shells and when they die, they fall to the ocean floor and the carbon gets sequestered down there.

有些贝壳类水生物用在水中溶解的二氧化碳去造碳酸钙的贝壳，并且当他们死后，他们身体沉入海底，碳就被隔绝在海底了。

So with all this carbon constantly being depleted from the atmosphere, we really need to keep carbon output up to a certain point.

所以因为碳持续性得从大气中消耗尽，我们真的需要提高碳产量让它维持在一个点上。

So why all the bad press for burning carbon?

所以为什么还会有关于燃烧碳的那么多负面的新闻呢？

Well, turns out it's the source of the carbon being burned that's the key.

嗯，结果表明燃烧的碳的来源是问题关键。

It's in fact the burning of what we call "fossil carbon" that creates the imbalance: fossil fuels, coal, oil, natural gas.

事实上是燃烧我们说的“化石碳”导致了这些不平衡：化石燃料，煤，石油，天然气。

These substances are all mined.

这些东西都是采掘出来的。

We have to dig them up or drill a well to release them.

我们必须要把他们挖出来或者钻一个井去得到他们。

And this is carbon that was in the atmosphere millions of years ago.

这些碳是几百万年前在大气中的碳。

So what happens is: when we burn this carbon, ok, it doesn't really release a whole lot compared to the amount that's already there in the atmosphere, but it adds to the pool.

所以事情是这样的：让我们燃烧这些碳，ok，跟已经在大气中的碳相比，燃烧他们释放的碳不是很多，但是他们增加了大气的碳总量。

And over years it accumulates.

多年来碳含量一直在累积。

Think of the atmosphere as a big bathtub.

把大气想成一个大的浴缸。

It's basically already filled to the brim with carbon.

里面已经装满了很多碳，就快溢出来了。

When we start adding fossil carbon into the mix, it starts to spill over.

当我们开始增加化石碳进去，大气里的碳就开始溢出。

That being said, there's actually a category that's in-between: what we call biomass fuels, probably the most common one is wood.

虽这么说，事实上有一种碳形式是在两者之间的：我们叫生物燃料，最常见的可能就是木材。

Another example, um, on the North American plains, the Native Americans used to collect buffalo droppings to burn.

另一个例子，在北美平原上，当地人过去常常收集水牛的粪便去燃烧。

Uh, in Ireland, they cut up peat from bogs and they burn that.

在Ireland，人们把泥塘里的泥煤切下来去烧。

So what's the big distinction between this and fossil carbon?

所以这种碳和化石燃料有什么大的区别？

Biomass carbon is what we might call current carbon.

生物燃料是我们说的流动性碳。

It's always going in and out of the atmosphere.

他们总是进出大气。

So if we burn one of these fuels, we're putting its carbon into atmosphere. Right?

如果我们燃烧了其中的碳，我们增加了大气中的碳含量，对吗？

But in a balanced system, somewhere else in the world the same amount of carbon is going back.

但是在一个平衡的系统里，世界上另一个角落里会减少同等量的碳。

It gets taken in by growing vegetation.

通过种植植被把这部分碳消耗掉。

So burning biomass fuel produces sort of not-so-bad carbon.

所以燃烧生物燃料产生的是那种不是很坏的碳。

In fact, it can become good carbon if we endeavor as a society, as humanity, to allow forests to recover this carbon, if we don't, say, pave over all the surfaces to prevent things from growing.

事实上，它可以成为好的碳如果我们整个社会整个人类努力让森林去消耗这些碳的话。如果我们不这么做，比如把地球上所有土地都为人类所用不让植物生长（他们就不会成为好的碳）。

So whenever we cut down a tree and burn its wood, we have to allow another tree to grow to keep things in balance.

所以无论什么时候我们砍掉一棵树，燃烧了木材，我们必须让另一颗树去成长去平衡这个体系。

That way, you're, you're carbon neutral.

那样的话，你就创造了中性碳。