万物简史 第377期:进入对流层(18)

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　　Indeed, meteorologists increasingly treat oceans and atmosphere as a single system, which is why we must give them a little of our attention here. 实际上，气象学家们越来越把海洋和大气看成是单一体系，因此我们在这里要多说几句。

　　Water is marvelous at holding and transporting heat. 水非常善于储存和传递热量——难以想像的大量热量。

　　Every day, the Gulf¹ Stream carries an amount of heat to Europe equivalent to the world's output of coal for ten years, 墨西哥湾暖流每天送到欧洲的热量，相当于全世界10年的煤产量。

　　which is why Britain and Ireland have such mild winters compared with Canada and Russia. 与加拿大和俄罗斯相比，为什么英国和爱尔兰冬天的气候比较温和，原因就在这里。

　　But water also warms slowly, which is why lakes and swimming pools are cold even on the hottest days. 但是，水热得很慢，因此即使在最热的日子里，湖泊和游泳池里的水也是凉的。

　　For that reason there tends to be a lag in the official, astronomical² start of a season and the actual feeling that that season has started. 由于这个原因，往往会有这样的情况：从天文学的角度来说，一个季节已经开始，而在实际的感觉上，还不到那个季节。

　　So spring may officially start in the northern hemisphere in March, but it doesn't feel like it in most places until April at the very earliest. 因此北半球的春季始于3月，而最早要到4月，大部分地方才有春天的感觉。

　　The oceans are not one uniform mass of water. 海水不是一个均匀的整体。

　　Their differences in temperature, salinity³, depth, density⁴, and so on have huge effects on how they move heat around, which in turn affects climate. 各地海水的温度、盐度、深度、密度等帮都存在差异，对海水传递热茧的方式有着巨大的影响，进而又影响到气候。

　　The Atlantic, for instance, is saltier than the Pacific, and a good thing too. 比如，大西洋比太平洋的盐度要高，这还是一件好事情。

　　The saltier water is the denser⁶ it is, and dense⁵ water sinks. 海水越咸，密度越大，密度大的海水下沉。

　　Without its extra burden of salt, 要是大西洋洋流不需要负担额外的盐量，

　　the Atlantic currents would proceed up to the Arctic, warming the North Pole but depriving Europe of all that kindly⁷ warmth. 就会一直推进到北极地区，使北极暖和起来，但欧洲会完全失去那些不可多得的热量。

　　The main agent of heat transfer on Earth is what is known as thermohaline circulation, 地球上热盘传递的主要载体是所谓的热盐对流。

　　which originates in slow, deep currents far below the surface—a process first detected by the scientist-adventurer Count von Rumford in 1797. 它源自海洋深处的缓慢洋流——这个过程是科学家、冒险家伦福德伯爵于1797年发现的。

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