万物简史 第380期:进入对流层(21)

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　　Eventually much of that limestone¹ will end up feeding volcanoes, and the carbon will return to the atmosphere and fall to the Earth in rain, 那些灰岩中的很大一部分最终会成为火山的原料，破将回到大气层，以雨的形式落在地球上。

　　which is why the whole is called the long-term carbon cycle. 因此，整个过程被称之为长时碳循环。

　　The process takes a very long time—about half a million years for a typical carbon atom, 该过程要花很长的时间才完成——对一个普通的碳原子来说，大约要花50万年，

　　but in the absence of any other disturbance² it works remarkably³ well at keeping the climate stable. 在没有别的因素干扰的情况下，这对保持气候稳定很起作用。

　　Unfortunately, human beings have a careless predilection⁴ for disrupting this cycle 不幸的是，人类却随意打乱这个循环，

　　by putting lots of extra carbon into the atmosphere whether the foraminiferans are ready for it or not. 把大量额外的碳排放到大气里，不顾有孔虫是否有了准备。

　　Since 1850, it has been estimated, we have lofted⁵ about a hundred billion tons of extra carbon into the air, 据估计，自1850年以来，我们已经额外向空气里排放了大约1000亿吨碳，

　　a total that increases by about seven billion tons each year. 这个数字又以每年大约70亿吨的速度增加。

　　Overall, that's not actually all that much. 总的来说，那实际上不算很多。

　　Nature—mostly through the belchings of volcanoes and the decay of plants—sends about 200 billion tons of carbon dioxide into the atmosphere each year, 大自然——主要通过火山喷发和树木腐烂——大约每年向大气里投放2000亿吨二氧化碳，

　　nearly thirty times as much as we do with our cars and factories. 差不多是我们的汽车和工厂排放量的30倍。

　　But you have only to look at the haze⁶ that hangs over our cities to see what a difference our contribution makes. 但是，你只要看一眼我们雾蒙蒙的城市或者科罗拉多大峡谷，有时候甚至是多佛尔的白垩，你就会明白，我们的参与造成了多大的差别。

　　We know from samples of very old ice that the "natural" level of carbon dioxide in the atmosphere, 我们从非常古老的冰样得知，大气里二氧化碳的“自然”浓度，

　　that is, before we started inflating⁷ it with industrial activity—is about 280 parts per million. 也就是说，在我们的工业活动开始雪上加霜之前的浓度——大约是百万分之二百八十。

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