Asymmetries in tropical rainfall and circulation patterns in idealised CO2 removal experiments
Asymmetries in tropical rainfall and circulation patterns in idealised CO2 removal experiments
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DOI：
10.1007/s00382-012-1287-2
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发表时间：
2013-01-01
期刊：
影响因子：
4.6
通讯作者：
Andrews, Timothy
中科院分区：
文献类型：
--
作者：
Chadwick, Robin;Wu, Peili;Andrews, Timothy
大气中二氧化碳的去除作为减排的补充，甚至替代减排，目前正受到认真的考虑。然而，这种战略对气候系统的可能后果，特别是对水文循环的区域变化的可能后果，还没有得到很好的理解。描述了两个理想化的大气环流模型实验，其中二氧化碳浓度沿着相同的路径稳步增加，然后降低。在二氧化碳开始减少后的几十年里，全球平均降水量继续增加。由于降水和水汽对全球环流的限制，平均热带环流显示出相关的变化。降水和环流变化的模式对于二氧化碳和全球平均温度的变化也表现出不对称性，但全球降水的滞后可以归因于同一温度状态下不同水平的二氧化碳，而区域变化则不能。相反，海洋记忆和热传递在这里很重要。特别是，在二氧化碳浓度下降期间，赤道东太平洋相对于西太平洋继续变暖，产生了异常大的赤道太平洋海面温度梯度和相关的降水异常。这种机制很可能是对东太平洋混合层水和下面的次温跃层水之间的大气强迫的反应滞后，原因是通过海洋环流输送。这项研究的含义是，大气中二氧化碳浓度先增加后减少的路径可能会导致二氧化碳减少期间的气候状态，而这种气候状态在增加期间没有经历过。
Atmospheric CO2 removal is currently receiving serious consideration as a supplement or even alternative to emissions reduction. However the possible consequences of such a strategy for the climate system, and particularly for regional changes to the hydrological cycle, are not well understood. Two idealised general circulation model experiments are described, where CO2 concentrations are steadily increased, then decreased along the same path. Global mean precipitation continues to increase for several decades after CO2 begins to decrease. The mean tropical circulation shows associated changes due to the constraint on the global circulation imposed by precipitation and water vapour. The patterns of precipitation and circulation change also exhibit asymmetries with regard to changes in both CO2 and global mean temperature, but while the lag in global precipitation can be ascribed to different levels of CO2 at the same temperature state, the regional changes cannot. Instead, ocean memory and heat transfer are important here. In particular the equatorial East Pacific continues to warm relative to the West Pacific during CO2 ramp-down, producing an anomalously large equatorial Pacific sea surface temperature gradient and associated rainfall anomalies. The mechanism is likely to be a lag in response to atmospheric forcing between mixed-layer water in the east Pacific and the sub-thermocline water below, due to transport through the ocean circulation. The implication of this study is that a CO2 pathway of increasing then decreasing atmospheric CO2 concentrations may lead us to climate states during CO2 decrease that have not been experienced during the increase.