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Today we think carbon dioxide as a dangerous gas,
如今我们认为二氧化碳是危险的气体
causing havoc through climate change.
它改变气候并因而引发浩劫。
but actually, carbon dioxide has always been vital to our planet
不过事实上，二氧化碳对地球而言，一直是至关重要的
because it traps heat in the atmosphere that would otherwise be lost to space.
二氧化碳有助于留住大气层内的热能 否则这些热量将散失到太空中。
To see just how critical carbon dioxide is to Earth,
为了理解二氧化碳对地球的重要性
take a look at our near neighbors.
看一下地球邻居的情况。
Mars is a frozen wasteland with an average temperature of minus 60 degree.
火星是一片冰冻荒原 平均为零下60度。
that is because, its atmosphere doesn't have enough carbon dioxide to keep it warm.
原因是火星大气层没有足够二氧化碳来保暖
At the other extreme,
金星处在另一个极端
is hot enough to melt lead,not simply because it's a bit coser to the Sun,
其表面温度高得足够融化铅 原因并不只是与太阳的距离更近
but because Venus has an atmosphere with thousands times more carbon dioxide than Earth.
也是因为金星大气中的二氧化碳含量为地球的数千倍
