An intensified hydrological cycle in the simulation of geoengineering by cirrus cloud thinning using ice crystal fall speed changes
An intensified hydrological cycle in the simulation of geoengineering by cirrus cloud thinning using ice crystal fall speed changes
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DOI：
10.1002/2015jd024304
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发表时间：
2016-06
期刊：
影响因子：
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通讯作者：
L. Jackson;J. Crook;P. Forster
中科院分区：
文献类型：
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作者：
L. Jackson;J. Crook;P. Forster
通过卷云减薄（CCT）对地球气候进行地球工程的提议可能比太阳辐射管理计划具有优势：北极的冷却放大，特别是对全球平均降水量的扰动较小。使用CCT的理想化气候模式实现，其中冰粒子下落速度增加2倍，4倍和8倍，我们研究了大气顶部有效辐射强迫（ERF），近地面温度和水文循环响应之间的关系。ERF与下降速度变化是非线性的，并由相反的正短波和负长波辐射强迫之间的权衡驱动。4倍和8倍下落速度下的ERF均为−2.0 Wm−2。全球平均温度随ERF呈线性下降，而北极温度的下降与全球平均变化相比被放大。全球平均降水量的变化涉及快速调整（~ 1%/Wm 2），与净大气能量平衡的变化呈线性关系，以及反馈响应（~2%/°C）。全球平均降水量和蒸发量在CCT的第一年强烈增加。大气垂直翻转环流的增强、有利于蒸发的边界层气候的变化以及地表可用于蒸发的能量增加（来自净短波辐射的增加和地下热量储存的减少）促进了水文循环的增强。这种水文循环的强化是CCT导致气候变冷的一个重要副作用。任何伴随的负面卷云反馈响应都会隐含地增加CCT部署的成本和复杂性。
Proposals to geoengineer Earth's climate by cirrus cloud thinning (CCT) potentially offer advantages over solar radiation management schemes: amplified cooling of the Arctic and smaller perturbations to global mean precipitation in particular. Using an idealized climate model implementation of CCT in which ice particle fall speeds were increased 2×, 4×, and 8× we examine the relationships between effective radiative forcing (ERF) at the top of atmosphere, near‐surface temperature, and the response of the hydrological cycle. ERF was nonlinear with fall speed change and driven by the trade‐off between opposing positive shortwave and negative longwave radiative forcings. ERF was −2.0 Wm−2 for both 4× and 8× fall speeds. Global mean temperature decreased linearly with ERF, while Arctic temperature reductions were amplified compared with the global mean change. The change in global mean precipitation involved a rapid adjustment (~ 1%/Wm2), which was linear with the change in the net atmospheric energy balance, and a feedback response (~2%/°C). Global mean precipitation and evaporation increased strongly in the first year of CCT. Intensification of the hydrological cycle was promoted by intensification of the vertical overturning circulation of the atmosphere, changes in boundary layer climate favorable for evaporation, and increased energy available at the surface for evaporation (from increased net shortwave radiation and reduced subsurface storage of heat). Such intensification of the hydrological cycle is a significant side effect to the cooling of climate by CCT. Any accompanying negative cirrus cloud feedback response would implicitly increase the costs and complexity of CCT deployment.