双语：NASA宣称全球将进入“大雨季”

　　As our planet continues to warm, the amount of rain that will fall in tropical regions will increase, research suggests.

　　研究表明，随着全球持续变暖，热带地区的降雨量将会增加。

　　The study found that global climate models may underestimate the amount of rain that will fall in these regions, because they underestimate decreases in high clouds over the tropics seen in recent NASA observations.

　　该研究发现，全球气候模型可能低估了这些地区的降雨量，因为它们低估了热带地区高空云层的减少——而NASA最近的观测则发现了这一点。

　　High-altitude tropical clouds trap heat in the atmosphere, but global warming appears to create fewer of these clouds, which would lead to the tropical atmosphere cooling - leading to increased tropical rainfall.

　　热带高空云层会阻隔大气中的热量，但是全球变暖似乎会使得这些云层减少，这就会使得热带大气冷却，导致该地区降雨量增加。

　　But how can fewer clouds lead to more rainfall?

　　但是云层减少了，为什么降雨量反而会增加呢?

　　Rainfall isn’t just related to the clouds that are available to make rain - but also to the Earth’s ’energy budget’ - incoming energy from the sun compared to outgoing heat energy.

　　因为雨量不仅与降雨云有关，也和地区的“能量预算”有关——即从太阳吸收得来的能量和地球外散的能量之比。

　　High-altitude clouds trap heat in the atmosphere, but if there are fewer of these clouds in the future, the tropical atmosphere will cool, and cooling water vapor condenses it, turning it into a liquid - rain.

　　高空云层可以阻隔大气中的热量不外泄，但是如果将来这些云层减少，热带大气就会冷却下来，就会使得水蒸气冷却，变成液态降雨。

　　The research, led by Dr Hui Su of NASA’s Jet Propulsion Laboratory in Pasadena, California, also found that the increased tropical rainfall would warm the air up again to balance the cooling from the high clouds shrinking.

　　该项研究由苏慧(音)博士、以及位于加州帕萨迪纳的NASA喷气推进实验室联合进行，还发现热带降雨的增加会使得空气再次升温，从而和高空云层缩减带来的冷却相平衡。

　　Rainfall warming up the air also sounds counter-intuitive, as people are used to rain cooling the air around them.

　　降雨会使空气升温听起来也有违直觉，因为人们一般都认为降雨会使空气降温。

　　However, several miles up in the atmosphere, a different process occurs.

　　但是，在离地面几英里的高空中，却出现了一个不同的过程。

　　When water evaporates into water vapor on Earth’s surface and rises into the atmosphere, it carries with it the heat energy that made it evaporate.

　　当水蒸发成地球表面的水蒸气并上升到大气中时，会携带着使其蒸发的热量。

　　But when the vapor reaches the cold upper atmosphere, it condenses into liquid droplets or ice, releasing its heat and warming the atmosphere.

　　但是当水蒸气遇到寒冷的上层大气，就会凝结成液态水滴或者冰晶，释放热量并使得大气升温。

　　The study, published in the journal Nature Communications, says the decrease in high tropical cloud cover is one result of a planet-wide shift in large scale-scale air flows occurring as Earth’s temperature warms.

　　该项研究被刊载在《自然通讯》期刊上，热带高空云层的减少，是由于地球气温变暖导致大规模空气流量发生大范围变化的结果之一。