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If you've been outside, like, even one time in your life, you know that the Sun plays a key role in the weather.
如果大家都在室外待过的话，哪怕只有一次，你们也一定会感受到太阳在天气中发挥的重要作用。
It's usually warmer during the day and colder at night, and a cloudy day feels a lot different from a sunny one.
天气一般都是白天暖一些，晚上凉一些，有云的时候跟晴天感觉大不相同。
But that's pretty obvious.
但这些都是明显的感受啦。
Here's a harder question: How much does the Sun affect Earth's climate?
这里问大家个不那么容易回答的问题：太阳对地球气候的影响有多大呢？
Like, beyond the fact that it keeps us from being a frozen hunk of space rock?
太阳可以保证地球不冻成一个冰块这件事儿，这里先不提。
After all, the Sun goes through all kinds of cycles and changes, so it seems like at least some of that should affect our planet, too.
毕竟太阳可以会经历各种周期和变化，所以似乎至少部分周期和变化也会影响到地球的行星。
It turns out that it does -- and has for billions of years.
事实也确实如此——而且这种影响已经延续了数十亿年了。
But it's definitely not the only variable.
但这当然不是唯一的变量了。
When scientists talk about the planet's climate, they're referring to long-term patterns of weather that can only be seen over long periods of time, like tens, hundreds, or even thousands of years.
科学家讨论的行星气候，是指长期的气候模式，只能通过长期的观察来得知。这里说的长期，可能是数十年、数百年，乃至上千年。
All kinds of things can influence this, so it makes sense that changes with the Sun, like with its energy output, would, too.
各种要素都会影响气候，所以说气候随着太阳的变化而变化也就合情合理了，就像气候也会随着能量输出的变化而变化一样。
After all, that's mainly where we get our heat.
毕竟，我们主要是从太阳获取能量。
The thing is, though, some solar changes don't always do what we think they should.
但问题在于，太阳的一些变化并不总是按套路出牌。
One way we can track the Sun is through the solar constant, which measures roughly the average amount of energy striking every square meter of the Earth.
有一种可以循迹的办法就是通过太阳常数，太阳常数可以大致估量出地球上每平方米上平均吸收的能量。
We've measured it at about 1.4 kilowatts per meter squared, but studies of other Sun-like stars suggest that number could have changed.
此前，根据我们的估量，太阳常数是1.4千瓦每平方米，但在研究了其他一些与太阳类似的哼醒后，我们发现太阳常数可能是在变化的。
The solar constant isn't very constant at all.
太阳常数并不是一成不变的。
In fact, early in Earth's life, it was likely 25 or 30% lower than what it is today, thanks to how processes inside the Sun have changed over its lifetime.
实际上，地球形成初期，太阳常数比现在低25%-30%左右，这是因为太阳内部的进程也会随着生命周期的演进而发生变化。
As a result, basic physics suggests that three billion years ago, Earth should've been as frozen as Hoth from Star Wars.
所以，基础物理学表明，30亿年前，地球跟《星球大战》里的霍斯星一样冷。
And some models suggest the Earth would've been frozen solid for something like two billion years after its formation.
一些模型显示，地球形成后，大概冰冻了近20亿年。
The problem is, that totally didn't happen according to the fossil record.
但根据化石记录，这一切并未曾发生过。
There's also evidence that Mars was warm and wet early on, exactly when the Sun should've been dim and cool.
还有证据表明：火星一开始是又暖又湿的，而那时候，太阳应该是灰暗寒冷的。
Planetary scientists often call this apparent contradiction the faint young Sun paradox.
行星科学家经常将这种截然相反的对比称为黯淡太阳悖论。
Since it was first realized in the late 1960s, astronomers, geologists, and climate scientists have tried basically every idea under the Sun to explain what happened.
自从上世纪60年代人类发现太阳以来，天文学家、地质学家、气候学家都穷尽脑汁去解释这些现象。
Some scientists think the Sun must be unusual or that Earth's orbit and rotation had to have been very different.
一些科学家认为，太阳一定有什么不同寻常之处，再不就是地球的轨道以及旋转情况与众不同。
Others argue that maybe clouds or the greenhouse effect work differently than we think.
还有些科学家认为，或许云或者温室效应的影响与我们理解的不同。
Fifty years later, we still don't have a good answer for why the Sun didn't affect Earth as much as it should've back then.
50年后，我们依然无法很好地解释太阳以前影响地球的力度为何不是理论上推断的那样。
But this paradox does make one thing clear: Even if the Sun can change our climate, it's not the only thing that affects it.
但这种悖论明确了一件事：即便太阳会改变气候，但太阳绝不是唯一一个可以改变气候的因素。
Even over shorter and more recent time spans, it isn't as constant as it might seem, and evidence suggests that those little changes have affected our planet, too -- at least, to a point.
即便在近代，太阳也不是它看起来的那样恒定，而且有证据显示，这些细微的变化可能也影响了地球，至少从某个角度来看是这样的。
For hundreds of years, scientists have tracked a pattern of activity on the Sun called the solar cycle.
几百年来，科学家一直在跟进太阳的一种活动形式，名作太阳活动周期。
Over the course of each 11-year cycle, magnetic forces in the Sun cause big variations in things like cool sunspots and explosive solar flares.
太阳活动周期是11年一个轮回，太阳内部的磁力造成了一些现象的巨大浮动，比如酷酷的太阳黑子，以及爆炸性的太阳耀斑。
Evidence recorded in the rings of trees also hints at longer and more subtle cycles spanning hundreds or even thousands of years.
许多树的年轮也表明数目的周期可能或长或缓，有时候是数百年，有时候是数千年。
It's hard to know for sure, but some of these cycles seem to match up with ancient changes in the climate.
很难精确得知具体的周期，但其中一些周期似乎与古时候的气候变化情况相吻合。
For instance, one study tracking solar activity from about 6000 years ago matched up periods when the Sun was calm with wetter environments here on Earth.
比如，关于近6000年前太阳活动的一项研究与另一个时期的情况相吻合。另一个时期就是指太阳不活跃，而地球环境潮湿的时期。
But it's not like the Sun directly caused floods or anything, so to know the whole picture, we'd need to understand everything else happening around that time.
但这跟太阳直接引发的洪水等现象不同，为了了解整个事情的来龙去脉，我们需要知道那个时期的所有情况。
In general, our star does seem to have played some role in our climate, but there's also a lot going on down here.
总体而言，太阳确实对地球气候造成了一定的影响，但还有很多需要考量的地方。
If nothing else, though, one thing we can say for sure is that these long-term solar patterns are definitely not causing the global warming of the last century.
其中一个可以肯定就是：长期的太阳模式并不是引起上世纪全球变暖的原因。
At most, the solar cycle results in a change in heat from the Sun of about 0.1%, or nearly 60 times less than what would cause the heating we see today.
满打满算，太阳周期只能提升0.1%的热量，这个热量是今天引发全球变暖热量的近1/60。
And, in fact, while the last few decades have experienced the most dramatic warming in millions of years, the Sun has been going through one of its least active periods on record.
而且，过去几十年里，是地球数百万年间气候变暖最严重的时期，但这个时期里，太阳确实史上最不活跃的时期之一。
So there's only one culprit for the rapid climate changes Earth is experiencing: us troublesome humans.
地球气候变化如此迅速的罪魁祸首只有一个：不消停的人类。
The overwhelming scientific consensus is that the recent warming of the Earth is due primarily to our production of greenhouse gases.
科学界有一个压倒性的共识：近期地球经历的全球变暖主要是因为我们产生了过多的温室气体。
There are lots of these, carbon dioxide possibly the most famous, and they're called that because they contribute to the greenhouse effect, or trapping of heat by Earth's atmosphere.
温室气体太多了，二氧化碳是其中最为人所知的。温室气体得名于此是因为它们导致了温室效应，使地球大气层累积了太多的热量。
That heat first arrives at the Earth as visible light from the Sun, but eventually it gets re-emitted by the surface in the infrared.
热量最开始是以可见光的形式来到地球，但最后以红外线的方式从地球表面放射出去。
Then, greenhouse gases block much of that infrared energy from escaping out to space, so it sticks around and warms up our climate.
然后，温室气体会阻止红外线能量跑到宇宙中，所以红外线就一直被阻隔在大气层之内，让地球气候越来越暖。
Now, some amount of greenhouse gas is a good thing, because it helps us stay warm.
一定量的温室气体是好事，可以保证温暖的环境。
But too much -- as you might already know -- is a really big problem.
但太多的温室气体——正如大家已经知道的这样——是个大问题。
At the end of the day, the Sun dominates almost every aspect of life here on Earth.
一天下来，太阳主导着地球生命的方方面面。
But that doesn't mean we're off the hook, either.
但这并不意味着我们就能摆脱困境了。
We're a pretty big variable all on our own.
人类本身就是非常大的不确定因素。
Thanks for watching this episode of SciShow Space!
感谢收看本期的《太空科学秀》！
If you'd like to learn more about how scientists study the Earth's climate and predict our future, you can watch our episode all about climate modeling over at the main SciShow channel.
如果大家想了解科学家研究地球气候并预测未来的方式的话，可以在《太空科学秀》频道的主栏目观看我们有关气候模拟的视频。
