Exeter-NCAR collaborative Development (EXTEND)

将全球平均气温保持在工业化前水平的1.5摄氏度或2摄氏度以内是人类应对气候变化的基石。气候模型模拟表明，即使将变化限制在比工业化前水平高1.5摄氏度的范围内，也会导致有害的极端气候增加，如区域和全球范围的热浪和极端降水事件，而这些极端情况在2摄氏度的温度目标下会进一步加剧。科学界认识到将全球平均温度限制在1.5或2.0 ℃的目标范围内的困难，导致越来越多的人呼吁通过所谓的“太阳辐射管理”技术进行气候干预，这些技术旨在增加行星的辐射，并引起冷却，以部分抵消全球变暖。SRM并不是一个新的想法，但这种方法极具争议性，许多科学，生态，道德和哲学论点反对这种建议。2021年3月，美国国家科学院在其SRM研究综合议程中建议对SAI进行稳健、公正、多模型的评估，资金流为2亿美元，并强调“该计划应从一开始就优先发展国际协调以及与其他国家共同发展研究”。海伍德是这项工作的理想合作伙伴。海伍德撰写了许多警示性研究，包括对亚马逊河降雨的有害遥相关影响，终止效应，对萨赫勒干旱和半球不对称SRM飓风频率的影响，并强调，任何实际的SRM部署都只应用于暂时缓解气候变化的最严重影响，同时过渡到净零碳经济。最近对SRM的评估支持谨慎和客观的分析，模型，可以代表详细的机制SRM。对于SAI，它们必须代表平流层的动力学和化学性质，如Brewer-Dobson环流、准两年振荡、与臭氧层有关的均相和非均相化学性质，以及详细的硫酸盐微物理演变，如气相氧化、成核、凝结、凝结、蒸发和重力沉降。这些动力学、化学和微物理过程决定了平流层硫酸盐气溶胶的空间分布和相关的辐射强迫，而且远比与充分混合的二氧化碳相关的过程复杂，后者的全球浓度和光谱特性是众所周知的。在最先进的GeoMIP G6 sulph实验中只有少数GCM足够;两个最好的模型可以说是英国气象局哈德利中心UKESM 1和美国国家大气研究中心（NCAR）CESM 2-WACCM这个提议使用英国的气候模型（UKESM 1）来扩展NCAR用CESM 2-WACCM开创的大集合方法。埃克塞特大学和NCAR之间的直接合作承诺利用两种目前最先进的GCM对SAI气候干预的各种利弊、危险和陷阱进行双模型评估。这项合作不仅将使英国科学界处于SAI气候干预的最前沿，该提案承诺可持续性，因为如果EXTEND得到资助，就有机会利用美国提议的资金流，2021年3月25日建议的2亿美元，特别是因为美国认识到“该计划应从一开始就优先发展国际协调和与其他国家共同发展研究”。因此，可持续性得到保证。

Maintaining global mean temperatures within 1.5C or 2C of pre-industrial levels is a cornerstone of humanity's battle against climate change. Climate model simulations suggest that even limiting change to 1.5C above pre-industrial levels will lead to increased detrimental climate extremes such as heat-waves and extreme precipitation events at a regional, and global scale and these extremes are further exacerbated under 2C temperature targets. The realization by the scientific community of the difficulty of limiting global mean temperatures to within these 1.5 or 2.0C targets has led to increased calls for climate intervention via so called "solar radiation management (SRM)" techniques which aim to increase planetary albedo and induce a cooling that acts to partially offset global warming. SRM is not a new idea, but such an approach is extremely controversial, with many scientific, ecological, moral and philosophical arguments against such proposals. In March 2021, The US National Academy of Sciences recommended in their integrated agenda for SRM research robust, unbiased, multi-model assessments of SAI with a funding stream of $200m, highlighting that "The program should, from the outset, prioritize development of international coordination and co-development of research with other countries". Haywood is an ideal partner for this work. Haywood has authored many cautionary studies including detrimental teleconnection impacts on Amazonian rainfall, termination effect, impacts on Sahelian drought and hurricane frequency of hemispherically asymmetric SRM, and stressed that any practical SRM deployment should only be used to temporally ameliorate the worst impacts of climate change whilst transitioning to a net carbon zero economy.Recent assessments of SRM support a cautionary and objective analysis using models that can represent the detailed mechanisms of SRM. For SAI, they must represent the dynamics and chemistry of the stratosphere such as the Brewer-Dobson circulation, the Quasi-biennial oscillation (QBO), homogeneous and heterogeneous chemistry relevant to the ozone layer, and the detailed sulphate microphysical evolution such as gas phase oxidation, nucleation, condensation, coagulation, evaporation and gravitational settling. These dynamical, chemical and microphysical processes determine the spatial distribution of stratospheric sulphate aerosol and the associated radiative forcing and are far more complex than those associated with well-mixed carbon dioxide where global concentrations and spectroscopic properties are well known. Only a handful of GCMs within the most advanced GeoMIP G6sulph experiment adequately; the two best models are arguably the UK Met Office Hadley Centre UKESM1 and the USA's National Center for Atmospheric Research (NCAR) CESM2-WACCM This proposal uses the UK's climate model (UKESM1) to EXTEND the large-ensemble approach pioneered by NCAR with CESM2-WACCM. Direct collaboration between the University of Exeter and NCAR promises a dual-model assessment of the various pros, cons, perils and pitfalls of SAI climate intervention utilising two of the most advanced GCMs currently available. The collaboration will not only position the UK scientific community at the forefront of SAI climate intervention, but provide a balanced assessment of the potential of SAI as a climate intervention strategy to policy-makers worldwide.The proposal promises sustainability as matched funding has been promised should EXTEND be funded and there are opportunities to tap into the USA's proposed funding stream of $200m that has been recommended on 25 March 2021, particularly as the USA recognises "The program should, from the outset, prioritize development of international coordination and co-development of research with other countries". Thus sustainability is assured.