PNAS2013-11-19 12:45 AM

Identifying external influences on global precipitation 全球降水的可识别外部影响

Abstract Changes in global (ocean and land) precipitation are among the most important and least well-understood consequences of climate change. Increasing greenhouse gas concentrations are thought to affect the zonal-mean distribution of precipitation through two basic mechanisms. First, increasing temperatures will lead to an intensification of the hydrological cycle (“thermodynamic” changes). Second, changes in atmospheric circulation patterns will lead to poleward displacement of the storm tracks and subtropical dry zones and to a widening of the tropical belt (“dynamic” changes). We demonstrate that both these changes are occurring simultaneously in global precipitation, that this behavior cannot be explained by internal variability alone, and that external influences are responsible for the observed precipitation changes. Whereas existing model experiments are not of sufficient length to differentiate between natural and anthropogenic forcing terms at the 95% confidence level, we present evidence that the observed trends result from human activities. 论文摘要 全球(包括海洋和陆地)降水量的改变是气候改变最重要和最未被充分理解的后果之一。温室气体的持续聚积可能是通过两种基础机制来影响降水量的纬度平均分布的。首先,温度的持续上升会导致水循环的强化(“热力学”的改变)。其次,大气环流模式的改变将导致风暴路径和亚热带干旱地区的极向位移和热带带(动态变化)的扩大。我们证明了这些改变在全球降水中同时发生,这一行径不能单一解释为内部变化原因,外部因素的影响对所观测到的降水变化也起了推波助澜的作用。然而现有的模型实验还未具有足够长度以95%的置信水平来鉴别自然和人类强制条件之间的区别。我们展示的证据证明所观测到的趋势是由人类行为活动所导致的。

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