Impacts of Climate Engineering Using Stratospheric Aerosols

“地球工程”是采取有目的的行动来抵消全球温室效应的想法，在这种情况下，通过人为增加地球的反射率，从而减少气候系统可用的太阳能。 该项目利用气候模型，特别是共同体地球系统模型（CESM），研究将硫酸盐注入平流层产生反射气溶胶的潜在后果，模拟大规模火山爆发的影响。该奖项是PI在AGS-1157525下先前工作的延续。PI和其他人先前的工作提出了平流层地球工程将导致季风降雨减少的担忧，对热带农业产生负面影响。在这里，PI提出，可以使用优先冷却南半球海洋的地球工程技术来减轻负面影响。 这一想法是基于研究表明，南半球的冷却将热带辐合带推向北方，从而优先在北方季风区造成更多的降雨。 数值实验将通过人为改变CESM模拟中的海洋表面温度来验证这一观点。本文的第二个主题是平流层硫酸盐注入对陆地植被和农业的影响。 以前的工作使用嵌入在气候模型中的植被模型表明，由于平流层气溶胶注入，光合作用略有减少，部分原因是平流层气溶胶散射阳光增加了漫射表面日射，牺牲了直射阳光（除了减少到达地面的总阳光）。 但其他影响也可能很重要，特别是由于气溶胶注入造成平流层臭氧减少而增加了紫外线阳光（火山爆发后的一种影响）。 增加紫外线对农业生产的影响进行了研究，通过使用社区土地模型（CLM），CESM的土地表面组件模型，使用CLM-Crop版本，允许农作物的代表。 除了与CESM的合作外，该项目还支持地球工程模型比较项目（GeoMIP），这是一个由多个气候模拟中心进行一系列模拟的国际合作项目，目的是评估可能的结果范围。 该项目支持为GeoMIP参与者举办年度讲习班，并正在启动一个作物模型模拟地球工程对农业影响的相互比较项目。 作物模型相互比较工作是在现有的全球网格作物模型相互比较（GGCMI）倡议下组织的，该项目的更广泛影响来自于需要进行研究，如向决策者和公众通报地球工程计划的潜在成本和效益。此外，CLM-Crop的拟议发展将为研究界提供更多的资源。该项目支持一名研究生和一名博士后，从而为未来的气候科学工作者提供支持。

"Geoengineering" is the idea of taking purposeful action to offset global greenhouse warming, in this case by artificially increasing Earth's reflectivity and thus reducing the solar energy available to the climate system. This project uses climate models, particularly the Community Earth System Model (CESM) to examine the potential consequences of injecting sulfate into the stratosphere to produce reflecting aerosols, mimicking the effect of large volcanic eruptions. The award is a continuation of previous work by the PI under AGS-1157525.Previous work by the PI and others raised concerns that stratospheric geoengineering would result in a reduction in monsoon rainfall, with negative impacts on tropical agriculture. Here the PI proposes that the negative impacts could be mitigated using a geoengineering technique that preferentially cools the Southern Hemisphere ocean. The idea is based on research suggesting that cooling the Southern Hemisphere pushes the intertropical convergence zone northward, thereby causing preferentially greater amounts of rainfall in Northern Hemisphere monsoon regions. Numerical experiments to test this idea would be conducted by artificially altering ocean surface albedo in CESM simulations.A second topic pursued here is the effect of stratospheric sulfate injection on terrestrial vegetation and agriculture. Previous work using vegetation models embedded in climate models suggests a small reduction in photosynthesis due to stratospheric aerosol injection, in part because scattering of sunlight by stratospheric aerosols increases diffuse surface insolation at the expense of direct sunlight (in addition to reducing total sunlight reaching the ground). But other effects could be important, in particular the increase in ultraviolet (UV) sunlight due to the reduction of stratospheric ozone as a consequences of aerosol injection (an effect seen following volcanic eruptions). The impact of increased UV on agricultural production is studied through the use of the Community Land Model (CLM), the land surface component model of CESM, using the CLM-Crop version which allows representation of agricultural crops. Some of the effort is devoted to developing CLM-Crop to include more crops and represent processes relevant to the UV impact.In addition to the work with CESM, the project also supports the Geoengineering Model Intercomparison Project (GeoMIP), a coordinated international project in which multiple climate modeling centers perform a specified set of simulations, so that the range of possible outcomes can be assessed. The project supports annual workshops for GeoMIP participants, and is also launching an intercomparison project for crop model simulations of the agricultural impacts of geoengineering. The crop model intercomparison effort is organized under the existing Global Gridded Crop Model Intercomparison (GGCMI) initiative.The broader impacts of this project stem from the need for studies such as this one to inform policy makers and the public regarding the potential costs and benefits of geoengineering schemes. In addition, the proposed developments to CLM-Crop will provide an enhanced resource for the research community. The project support a graduate student and a postdoc, thereby providing for the future climate science workforce.