Because warm air can hold more moisture than cool air, the relative humidity will be constant only if the amount of water vapor in the atmosphere increases as the temperature rises.

因为温暖的空气比冷空气能容纳更多的湿气，所以只有当大气中的水蒸气量随着温度的升高而增加时，相对湿度才会保持不变。

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An increase in temperature, for example, can boost the moisture content of the atmosphere, which then causes further warming because water vapor is a greenhouse gas.

例如，温度的升高会增加大气中的水分含量，这又会导致进一步的变暖，因为水蒸气是一种温室气体。

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The assumption of constant relative humidity is important, because water vapor in the atmosphere is another efficient absorber of radiation at infrared wavelength.

相对湿度恒定的假设是重要的，因为大气中的水蒸气是红外波长辐射的另一种有效吸收剂。

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Now most of that increase occurred after 1970, and it's an indication that there's more water vapor in the atmosphere so that these storms get invigorated.

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