The contrasting rainfall between the wet tropics and the dry subtropics largely determines the climate of the tropical zones. A southward shift of these rain belts has been observed throughout the latter half of the twentieth century, with profound societal consequences. Although such large-scale shifts in rainfall have been linked to interhemispheric temperature gradients from anthropogenic aerosols, a complete understanding of this mechanism has been hindered by the lack of explicit information on aerosol radiative effects. Here we quantify the relative contributions of radiative forcing from anthropogenic aerosols to the interhemispheric asymmetry in temperature and precipitation change for climate change simulations. We show that in model simulations the vast majority of the precipitation shift does not result from aerosols directly through their absorption and scattering of radiation, but rather indirectly through their modification of cloud radiative properties. Models with larger cloud responses to aerosol forcing are found to better reproduce the observed interhemispheric temperature changes and tropical rain belt shifts over the twentieth century, suggesting that aerosol–cloud interactions will play a key role in determining future interhemispheric shifts in climate.

中文翻译：

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人为气溶胶-云相互作用驱动的半球气候变化

湿热带与干亚热带之间形成鲜明对比的降雨在很大程度上决定了热带地区的气候。在整个二十世纪后半叶，这些雨带向南转移，给社会带来了深远的影响。尽管这种大规模的降雨变化与人为气溶胶引起的半球温度梯度有关，但由于缺乏关于气溶胶辐射效应的明确信息，妨碍了对该机制的全面理解。在这里，我们为气候变化模拟量化了人为气溶胶辐射强迫对温度和降水变化的半球间不对称性的相对贡献。我们显示，在模型模拟中，绝大部分的降水变化不是由气溶胶直接通过其吸收和散射辐射引起的，而是间接地通过其对云辐射特性的改变而引起的。发现对气溶胶强迫具有较大云响应的模型可以更好地重现20世纪观测到的半球温度变化和热带雨带变化，这表明气溶胶-云相互作用将在确定未来的半球气候变化中发挥关键作用。