大西洋经向翻转环流(AMOC)能够将热量从热带地区传输到寒冷的北半球高纬度地区，并将大气中的碳和热量储存到深海中，在促进全球热量再分配和减缓气候变暖等方面都发挥至关重要的作用。观测与模拟结果表明，近年来，随着温室气体排放增加，AMOC强度有所减弱，并将在未来变暖情景中持续减弱，会给全球气候系统带来深远影响。为缓解温室气体强迫导致的全球变暖，相关学者提出了地球工程(Geoengineering)的备选治理理念，即采用大规模人为技术手段对全球气候进行干预。太阳辐射干预(Solar Radiation Modification, SRM)是一种基本的地球工程方法，是指利用人工方法大尺度改变地-气系统的辐射平衡，旨在通过减少入射的太阳短波辐射或增加逃逸到太空的长波辐射来缓解全球变暖。目前讨论度相对较高的四种太阳辐射干预方法分别为太空遮阳、海表反照率干预、平流层气溶胶注入以及海洋云增白。这几种方法在技术难度、作用区域、辐射干预高度等方面都有所区别，可能会导致其对气候系统的影响存在差异。因此，比较不同太阳辐射干预方法对气候系统的影响差异十分重要。太阳辐射干预有望通过降低地表温度来缓解全球变暖导致的AMOC减弱。已有相关研究证明了太空遮阳和平流层气溶胶注入缓解AMOC强度减弱的有效性，但是对海洋云增白和海表反照率干预的影响研究仍不充分，而且关于不同太阳辐射干预方法对气候系统的影响差异研究仍不充分。 
本研究利用6个地球系统模式，在四个太阳辐射干预试验情景(G1、G1ocean-albedo、G4和G4cdnc)及两个温室气体排放情景(Abrupt4×CO2和RCP4.5)下的模拟数据，分析四种不同太阳辐射干预方法(太空遮阳、海表反照率干预、平流层气溶胶注入和海洋云增白)相比于变暖情景下AMOC强度的变化，评估太阳辐射干预方法对气候变暖导致的AMOC变化的缓解效果，比较四种太阳辐射干预方法之间缓解AMOC变化的有效性差异，并分析了AMOC变化的驱动因子和物理机制。研究结果表明： 
(1) 两种温室气体排放情景(Abrupt4×CO2和RCP4.5)对AMOC的强度具有明显的减弱作用(分别减弱约6Sv和2.1Sv)，四种太阳辐射干预方法都能够有效缓解AMOC的减弱，但是不能完全将AMOC强度恢复到工业化前水平。其中，太空遮阳缓解AMOC减弱的效果明显强于其它三种方法；海洋云增白缓解AMOC减弱的有效性略强于平流层气溶胶注入，但是二者之间的有效性差异不显著；海洋云增白、平流层气溶胶注入和海表反照率干预对于缓解AMOC减弱的效果相似。 
(2) 四种太阳辐射干预方法下AMOC强度发生变化的主要驱动因素是北大西洋深对流区域(拉布拉多海、伊尔明厄海、北欧海)内海洋到大气的热通量。北极海冰面积变化也能通过北大西洋淡水通量机制影响AMOC强度，但相比之下，海气热通量变化对AMOC强度的影响更明显。AMOC将携带热量的表层海水传输到北大西洋深对流区域内，在该区域内海洋温度通常高于近地表气温，表层海水向大气中释放热量并冷却下沉。全球变暖增加大气温度，减少海洋向大气的热通量传输，削弱表层海水冷却下沉，进而减缓AMOC。四种太阳辐射干预方法都能够降低气温，部分恢复温室气体强迫减小的海气温差，增加海洋到大气的热通量，促进表层海水冷却下沉，增强AMOC。虽然四种太阳辐射干预方法都可以通过冷却大气来增强AMOC，但海气热通量仍弱于piControl情景，所以太阳辐射干预方法不能完全将AMOC强度恢复到工业化前水平。且不同太阳辐射干预方法之间缓解AMOC减弱的有效性差异与它们之间的海气热通量差异显著相关。 
(3)太阳辐射干预方法下AMOC强度变化对北大西洋不同区域的表层海水北向热量传输的影响不同。北向热量传输对不同气候情景的响应，在60°N附近发生变化。气候变暖导致AMOC减弱，减少了北大西洋中纬度地区的北向热量传输，但却微弱增加了高纬度地区向极地海洋的热量传输。四种太阳辐射干预方法都能够有效缓解大西洋表层海水，在中纬度地区热量传输的减弱和在高纬度地区热量传输的增强。但是高纬度表层海水北向热量传输对不同太阳辐射干预方法的响应不显著，其与北极海冰面积之间的相关性也很低。即在四种太阳辐射干预方法下，AMOC强度没有通过影响表层海水的北向热量传输来直接驱动北极海冰面积的变化。 

Atlantic meridional overturned circulation (AMOC) plays a vital role in promoting global heat redistribution and slowing global warming. It can transport heat from the tropics to high latitudes of the northern hemisphere, and transport carbon and heat from the atmosphere to the deep ocean for storage. The observation and simulation results show that with the increase of greenhouse gas emissions, the intensity of AMOC has weakened in recent years, and it will continue to weaken in the future warming scenario. The weakening of AMOC will have a far-reaching impact on the global climate system. Geoengineering, that is the deliberate and large-scale manipulation of the Earth’s climate, has been proposed as a way to mitigate or offset some of the impacts of anthropogenic global warming. Solar Radiation Modification (SRM) is one of the fundamental geoengineering methodologies, reducing the net solar shortwave radiation reaching Earth or increasing the outgoing longwave radiation, thus balancing longwave greenhouse gas (GHG) forcing. Space-Based Sun-shade (SBS) which simply blocking some incoming solar radiation before it reaches the Earth, Stratospheric aerosol injection (SAI) whereby aerosols aloft reflect incoming solar radiation, Marine cloud brightening (MCB) that is introducing aerosols into the marine boundary layer and thereby increasing cloud droplet numbers and hence their reflectivity, and Ocean albedo modification that is increasing the reflection of solar radiation by increasing the albedo of the ocean surface are the most commonlydiscussed methods.The four methods are different in technical difficulty, action area and the height of radiation modification, which may lead to the difference of climate effects. Therefore, it’s very important to compare the climate effects of different solar radiation modification methods. Solar radiation modification is expected to mitigate the weakening of AMOC caused by global warming. Relevant studies have proved the effects of SBS and SAI to mitigate AMOC weakening, but to now, the research on the effects of MCB and OAM are still insufficient. Moreover, few studies have systematically compared the climate impact differences caused by different solar radiation modification methods, especially in high latitudes. 

Based on the output data of six earth system models under four solar radiation modification scenarios (G1, G1ocean-albedo, G4 and G4cdnc) and two greenhouse gas emission scenarios (Abrupt4×CO2 and RCP4.5), this study evaluates the mitigation effect of different solar radiation modification types (SBS, OAM, SAI and MCB) on the change of AMOC intensity relative to greenhouse gas emission scenarios, compares the mitigation effectiveness differences of the four differenct solar radiation modification scenarios, compares the effectiveness of four differenct solar radiation modification scenarios to mitigate the AMOC weakening, and analyzes the driving factors and physical mechanisms of AMOC changes. The main results of this study are as follows:

(1) The two greenhouse gas emission scenarios (Abrupt4×CO2 and RCP4.5) can significantly weaken AMOC (about 6 Sv and 2.1 Sv respectively). The four solar radiation modification scenarios can effectively mitigate the weakening of AMOC, but these scenarios can not completely restore the intensity of AMOC to the pre-industrial level (piControl). The effect of SBS to mitigate the weakening of AMOC is significantly stronger than the other three scenarios. The mitigate effect of MCB is slightly stronger than that SAI, but the difference is no significant. The effects of MCB, SAI and MCB on mitigating the weakening of AMOC are similar. 
(2) The main driving factor for the AMOC changes under the four solar radiation modification scenarios is the sea-air heat flux in the North Atlantic deep convection regions (Labrador Sea, Irminger sea and Nordic sea). The change of Arctic sea ice area can also affect AMOC through the mechanism of North Atlantic fresh water flux, but the impact of sea-air heat flux on AMOC is more obvious. AMOC transprots the warm surface seawater to the North Atlantic deep convection regions, where the ocean temperature is usually higher than the atmosphere temperature. The surface seawater releases heat into the atmosphere, then cools and sink. Global warming increases the atmospheric temperature, reduces the heat flux transmission from the ocean to the atmosphere, weakens the cooling and sinking of surface seawater, slows down AMOC. The four solar radiation modification scenarios can reduce the temperature, partially restore the ocean-atmosphere temperature difference forced by greenhouse gases, increase the heat flux from the ocean to the atmosphere, promote the cooling and sinking of surface seawater, and enhance AMOC. Although the four solar radiation modification scenarios can enhance AMOC by cooling the atmosphere, the sea-air heat flux is still weaker than the piControl scenario, so the solar radiation modification can not completely restore the AMOC intensity to the pre-industrial (piControl) level. The effectiveness of different solar radiation modification scenarios to mitigate AMOC weakening is also significantly related to the difference of sea-air heat flux between them.
(3) AMOC changes under different solar radiation modification scenarios will affect the northward heat transport of surface seawater in the North Atlantic. Northward heat transport anomalies under different solar radiation modification scenarioschange sign at about 60°N. Global warming leads to the weakening of AMOC, which reduces the northward heat transport in the middle latitudes (30°N -50°N) of the North Atlantic, but slightly increases the heat transport from the high latitudes (60°N -70°N) to the polar ocean. The four solar radiation modification scenarios can effectively mitigate the weakening of northward heat transport in mid latitudes and the enhancement of northward heat transport in high latitudes. However, the response of the northward heat transport of high latitude surface seawater to different solar radiation modification scenarios is not significant, and the correlation with the Arctic sea ice area is low.