相反，当大气二氧化碳浓度低时，气孔密度似乎增加了——就像长出更多的嘴来呼吸。

Conversely, when atmospheric carbon dioxide is low, stomatal density tends to increase - it's like getting more mouths to breathe with.

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林木和其他类植物可以维持星球适宜温度，但是大气中二氧化碳浓度的增加会减低这种调节作用。

Trees and other plants help keep the planet cool, but rising levels of carbon dioxide in the atmosphere are turning down this global air conditioner.

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但是，二氧化碳浓度在一直增加。

But CO2 levels continue to rise.

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