On our planet, we have two polar regions:
地球上有两块极地：
the Arctic, whose name comes from the Greek Arktikos, of the North, and the Antarctic from Antarktikos, opposite of the North.
一个是北极，名字来自于希腊文，代表北方的意思，另一个是南极，也是来自于希腊文，意思是与北方相反。
But there's an easier way to remember them if you just remember what surrounds them.
有一个记住它们的更简单的方法，只要你知道它们周围是什么就可以了。
The Arctic, situated in the Northern hemisphere of our planet, is an ocean entirely surrounded by land.
北极, 在地球的北半球，是一块几乎被陆地包围的海洋。
On the other side of the world, the Antarctic is a continent entirely surrounded by ocean.
在世界的另一端，南极是一块大陆，几乎被海洋包围着。
So, the Arctic has polar bears but no penguins, and the Antarctic has penguins but no polar bears.
所以北极有北极熊而没有企鹅，南极有企鹅但是没有北极熊。
Let's talk about the Arctic first.
我们先来讲讲北极吧。
The Arctic region consists of a vast, ice-covered ocean surrounded by treeless permafrost.
北极有一块很大、被冰雪覆盖着的海洋，四周是没有树木的永冻土。
The area can be defined as the region between the Arctic Circle and the North Pole.
这一区域可以说是位于北极圈以及北极点之间的地方。
If you were to stand at the North Pole, everywhere you looked, in all directions, would be south.
如果你站在北极点上，无论你向哪个方向看都是南方，
But standing at the North Pole is difficult to do for very long
但是站在北极点上，你没办法站太久，
because it's in the middle of an ocean, covered by constantly shifting, frozen sea ice.
因为你是在海洋中间，被不断移动的海冰覆盖。
If you were to fall into the water at the North Pole, you'd fall into water that's 13,980 feet deep.
如果你掉到北极的海洋里，你会落到13980英尺这么深。
Above the water, average winter temperatures can be as low as -40 degrees Celsius,
水面上，冬天的平均温度可以低于零下40摄氏度，
and the coldest recorded temperature is approximately -68 degrees Celsius.
纪录中最冷的温度几乎到了零下68摄氏度以下。
Despite these incredibly harsh conditions, humans have populated areas in the Arctic for thousands of years.
虽然这儿的生活很艰困，还是有人居住在北极长达数千年了。
Life in the Arctic includes organisms living in the ice, zooplankton and phytoplankton,
居住在北极的其它生物还有浮游生物和植物，
fish and marine mammals, birds, land animals, plants, and human societies.
鱼、海洋哺乳类动物、鸟类、陆地动物、植物以及人类。
Okay, what about Antarctica?
好，那么南极呢?
Antarctica is Earth's southernmost continent, and it contains the geographic South Pole.
南极是地球最南方的大陆，它包含南极点。
It's the fifth largest continent on the planet at nearly twice the size of Australia.
南极是地球上第五大的大陆，几乎是澳洲的两倍大。
Almost 98% of Anarctica is covered by ice at least one mile in thickness.
几乎98%的南极大陆被冰雪覆盖，厚度起码有1英里。
Conditions in Antarctica are some of the most extreme in the entire world.
南极的生活环境可以说是世上最极端的一种。
On average, it's the coldest, windiest, driest continent and has the highest average elevation of all the continents.
平均而言，相较于所有大陆，这里最冷，风最大，最干燥，平均海拔最高。

You might think that it snows all the time at the Poles, but Antarctica is so dry,
你也许认为, 极地一年四季都在下雪，但是南极这么干燥，
it's considered a desert with annual precipitation of only 200 millimeters along the coast and far less inland.
可以说是一个沙漠，海岸沿线地区的年降雨量只有两百毫米，越往内陆越少。
The temperature in Antarctica has reached -89 degrees Celsius.
南极的温度可达到零下89摄氏度以下。
Because it's so harsh and hard to get to, there are no permanent human residents on Antarctica,
因为气候环境太恶劣，也太难抵达，所以南极没有永久居住的人类，
but anywhere from 1,000 to 5,000 people reside throughout the year at the research stations scattered across the continent.
只有一千到五千人左右在南极居住一年，住在遍布于南极的观测站。
Even the most extreme animals fight for survival, and only cold-adapted organisms survive there,
甚至最凶猛的动物都要为生存而战，也只有适应寒冷的动物能够生存，
including many types of algae, animals, bacteria, fungi, plants, and protista.
像是某些种类的水藻，动物，细菌，真菌，植物以及原生生物。
But why is Antarctica colder than its northern cousin?
但为什么南极比北极还要冷呢?
Well, first, much of the continent is more than three kilometers above sea level, and temperature decreases with elevation.
首先，和陆地有关，南极陆地在海平面三公里以上，温度随着海拔升高而下降。
That's why mountaintops have snow on them.
这也就是为什么山顶上会有雪。
Second, remember that the Arctic is really a frozen ocean.
第二，还记得北极是冰冻的海洋吗？
The water in the ocean beneath it is warmer than the frozen ground in the Antarctic,
在冰层底下的海水比南极冰冻的大陆要温暖的多，
and that warmth is transferred through the ice pack.
浮冰群会传递温度。
This prevents temperatures in the Arctic regions from reaching the extremes typical of the land surface of Antarctica.
这也会让北极的温度不会低到像南极那么极端。
Third, the seasons are conspiring against the Antarctic.
第三，季节也促成南极的冰冷气候。
During the aphelion in July, when the Earth is the farthest away from the Sun,
在七月的远日点，也就是地球离太阳最远的时候，
it also happens to be winter in the Antarctic, which creates a double-whammy of cold for the southern pole.
刚好也是南极的冬天，因此造就了这冷上加冷的南极气候。
But despite being inhospitable, the North and South Pole are a big reason why our planet is the way it is.
尽管不适合人居住，但是南北极依然是解释现今地球样貌何以如此的主要原因。
Both of our polar regions are very important climate controllers.
这两块极地是控制气候的重要因素。
They help moderate the temperature in our temperate zones and give us stable weather.
极地会舒缓温带地区的温度，给我们稳定的天气。
As sea ice in the Arctic declines due to climate change and global warming,
北极的海冰减少，是因为气候变化以及全球变暖，
weather around the globe becomes increasing more unstable.
因此地球的天气正变得越来越不稳定。