If you've been to a beach before, you've probably noticed a sort of line where the ocean water meets the land.

如果你曾經去過海邊，你可能會注意到海水與陸地間的某種交界線。

Of course ocean water doesn't stay at the same level all the time.

當然，海水不會一直維持在同一個水平面上。

Waves and tides cause the level of the water to rise and sink all day long.

波浪和潮汐會導致海水整天的上升和下降。

But we can measure the height of ocean water many times a day and figure out the water's average, or typical, height.

但我們每天都可以多次測量海水的高度，並計算出海水的平均（或是典型）高度。

The average height of the ocean in a particular place is called the local sea level.

特定地點的海洋平均高度被稱為「地方平均海面」。

But the ocean covers most of our planet.

但海洋覆蓋了地球大部分的面積。

So, it's way too big to measure with just a ruler.

所以它廣大到無法以尺進行測量。

NASA measures the average sea level of the whole ocean from space.

NASA 會從太空測量整個海洋的平均海平面。

This measurement is called the global sea level.

這項度量衡被稱為「全球海平面」。

People have been measuring local sea level at certain locations along the coast for hundreds of years,

數百年來，人們都在沿岸某些地點測量地方平均海面，

and NASA has been measuring the global sea level for almost three decades.

而 NASA 近三十年來則持續地測量全球海平面。

Over this time, scientists have observed that the global sea level has been rising.

這段時間內，科學家們觀察到海平面不斷地上升。

The ocean is about 7 to 8 inches higher now than it was a century ago.

海平面相較一世紀之前上升了 7 至 8 英吋。

Why?

為什麼？

Because Earth is getting warmer.

因為地球正在暖化。

Glaciers and ice sheets are large masses of ice that sit on land.

冰川和冰層是在陸地上的大型冰體。

As our planet warms, this ice melts and flows into the ocean.

隨著地球暖化，這些冰會融化並流入海洋。

More water in the ocean makes the sea level rise higher.

海洋中的水量增加會使海平面上升更高。

But that's not the only way seas are rising.

但這並不是海平面上升的唯一因素。

As Earth warms, the ocean is warming, too.

隨著地球暖化，海水也會跟著變暖。

Water expands as it gets warmer.

水會隨著溫度上升而膨脹。

So, warm water takes up more room in the ocean, making sea levels higher.

因此，溫暖的海水在海洋中佔據更多空間，讓海平面更高。

Rising sea levels can have an impact on how we live, especially in communities near the coasts.

上升的海平面可能會對我們的生活造成影響，尤其是沿海社區。

NASA and its partners use the Jason satellites to measure global sea level.

NASA 與其合作夥伴透過傑森衛星來測量全球海平面。

It takes approximately 10 days for the satellites to complete one measurement.

衛星完成一次完整測量大約需要 10 天。

And after they finish one measurement, they start measuring all over again.

當結束一次測量後，它們會開始重新測量。

By keeping an eye on Earth's oceans like this, we can measure how much sea level is rising and how quickly it is happening.

藉由這種方式密切關注海洋，我們能夠測量海平面上升的高度和速度。

Find out more about our planet at NASA Climate Kids.

請到 NASA Climate Kids 獲得更多相關資訊。