Climate Engineering by Arctic Winter Cirrus Thinning: Risks and Feasibility (AWiCiT)

讨论了气候工程(CE)方法作为抵消气候变化负面影响的可能工具。除了二氧化碳去除和太阳辐射管理外，还提出了一种方法，该方法建议通过减少卷云的变暖效应来增加传出的长波辐射，我们计划在这项提议中采取后续行动。为了最大限度地关注长波辐射，我们将重点放在冬季北极卷云的稀疏上，目的是回答以下问题：北极冬季卷云稀疏(AWiCiT)可行吗？可以实现的最大降温幅度是多少？AWiCiT的风险和副作用将根据北极平流层的可能变化，包括通过应用ICON-ART天气化学预报模型可能改变臭氧层和低层云，在区域范围内进行研究。将利用全球气溶胶-大气-海洋耦合气候模式MPI-ESM-HAM处理对全球环流、洋流和海冰覆盖的可能影响。为了解决这些问题，我们需要验证当前的模型是否足够好来解决上面提出的问题。特别是，它们能否再现北极冬季观测到的卷云的范围和垂直分布？在北极冬季的动态条件下，天然和播种成冰颗粒(INP)的输送途径是什么？需要对它们进行研究，以便估计所需区域中种子粒子的寿命。高空飞行的商用飞机的高度和航线是否足以播种相当一部分北极卷云，或者播种区域是否应该扩大到中纬度？在这种条件下，目前提出的可见气溶胶粒子BiJ3是最好的播种剂吗？只有当天然卷云主要通过溶液液滴的均匀冻结形成时，卷云变薄才有效。如果它们主要是由INP上的异质冻结形成的，播种可能会导致过量播种，导致增温而不是降温。因此，需要评估卷云的性质，特别是在当今气候条件下，异质冰冻对其形成的贡献。

Climate Engineering (CE) methods are discussed as possible instruments to counteract negative climate change impacts. In addition to carbon dioxide removal and solar radiation management, a method that suggests increases in the outgoing longwave radiation by reducing the warming effect of cirrus clouds has been proposed and that we plan to follow up in this proposal. In order to maximize the focus on longwave radiation, we focus on thinning of Arctic cirrus in winter with the goal to answer the following question: Is Arctic winter cirrus thinning (AWiCiT) feasible and what is the maximum extent of cooling that could be achieved? The risks and side effects of AWiCiT will be studied regionally in terms of possible changes in the Arctic stratosphere including possible modifications of the ozone layer and lower-lying clouds by applying the ICON-ART weather-chemistry forecast model. Possible effects on the global circulation, ocean currents and sea ice coverage will be addressed using the coupled aerosol-atmosphere-ocean global climate model MPI-ESM-HAM. In order to address these questions, we need to validate if the current models are good enough to tackle the questions formulated above. In particular, can they reproduce the observed extent and vertical distribution of cirrus in the Arctic winter? What are the transport pathways of natural and seeding ice nucleating particles (INP) under the dynamic conditions of the Arctic winter? They need to be studied in order to estimate the lifetimes of seeding particles in the desired region. Are the altitudes and routes of the high-flying commercial aircraft sufficient to seed an appreciable fraction of Arctic cirrus or should the seeding area be extended to mid-latitudes? Is under these conditions Bismuth-Tri-iodide (BiJ3), the currently proposed seeing aerosol particle the best seeding agent? Cirrus thinning is only effective if the natural cirrus form predominantly by homogeneous freezing of solution droplets. If they mainly form by heterogeneous freezing on INP, seeding could cause an overseeding leading to a warming instead of a cooling. Therefore the cirrus properties, especially in terms of the contribution of heterogeneous freezing to their formation in the present-day climate, need to be assessed.