Impacts of Climate Engineering Using Stratospheric Aerosols

“地球工程”是指采取有目的的行动来抵消全球温室效应变暖的想法，在这种情况下，通过人为地增加地球的反射率，从而减少气候系统可用的太阳能。该项目使用气候模型，特别是社区地球系统模型（CESM）来研究向平流层注入硫酸盐以产生反射气溶胶的潜在后果，模拟大型火山爆发的影响。该合同是美国空军在AGS-1157525项目下工作的延续。PI和其他人之前的工作引起了人们的担忧，即平流层地球工程将导致季风降雨减少，对热带农业产生负面影响。在这里，PI建议可以使用一种优先冷却南半球海洋的地球工程技术来减轻负面影响。这一想法是基于一项研究，该研究表明，南半球的降温推动了热带辐合带向北，从而优先导致北半球季风区的降雨量增加。在CESM模拟中，通过人为改变海洋表面反照率来进行数值实验来验证这一想法。本文探讨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。先前使用嵌入在气候模型中的植被模型的工作表明，由于平流层气溶胶的注入，光合作用会有轻微的减少，部分原因是平流层气溶胶对阳光的散射增加了漫反射的表面日照，以牺牲直射阳光为代价（此外还减少了到达地面的总阳光）。但其他影响可能也很重要，特别是由于气溶胶注入导致平流层臭氧减少（火山爆发后出现的效应），紫外线（UV）阳光增加。通过使用社区土地模型（CLM），即CESM的土地表面成分模型，使用允许表示农作物的CLM- crop版本，研究了紫外线增加对农业生产的影响。一些工作致力于开发CLM-Crop，以包括更多的作物，并代表与紫外线影响相关的过程。除了与CESM合作外，该项目还支持地球工程模型比对项目（GeoMIP），这是一个协调的国际项目，由多个气候模拟中心执行一组特定的模拟，以便评估可能结果的范围。该项目支持为GeoMIP参与者举办年度研讨会，并且还启动了一个相互比较项目，用于模拟地球工程对农业的影响的作物模型。作物模型比对工作是在现有的全球网格作物模型比对（GGCMI）倡议下组织的。这个项目的更广泛的影响源于需要进行这样的研究，以便让决策者和公众了解地球工程方案的潜在成本和收益。此外，拟议的CLM-Crop开发将为研究界提供一个增强的资源。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劳动力提供支持。

"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.