UKESM 1 Year Extension

全球气候变化是人类面临的主要环境威胁之一。要制定适当的缓解和适应战略，就需要准确预测地球气候的未来状况。为了解决这个问题，我们开发并使用了描述耦合气候系统中主要物理过程的全球气候模式（GCMs）。在观测到的主要温室气体、气溶胶和土地利用估计值的强迫下，这些模式在模拟时间内向前整合，从工业化前时期到现在。在一系列温室气体、气溶胶和土地利用情景的影响下，这些模型将持续到未来。然后，每个模型的未来气候都可以与模拟的当前气候进行比较。这一分析得出了一整套气候变化估计，可用于评估模拟变化的社会经济和生态影响，并有助于制定缓解和适应政策。gcm已经进一步发展为地球系统模型（esm），正如我们在UKESM LTSM中成功做到的那样，其中UKESM1是从耦合物理模型HadGEM3-GC3.1发展而来的。esm和gcm之间的一个关键区别是前者包括对全球碳循环的交互式描述，支持对物理气候变化和人为排放的二氧化碳被自然碳库吸收效力的潜在变化的分析。地球天然碳库吸收效率的降低可能导致排放的二氧化碳在大气中保留的比例更大，从而使地球变暖。因此，准确估计全球气候系统和碳循环的未来演变，对于清晰地了解人类未来面临的风险，以及制定缓解行动（通常针对碳吸收的有效性）以将全球变暖控制在危险水平以下至关重要。为了满足这一需求，我们开发了第一个英国地球系统模型（UKESM1），并在第六次耦合模式比对项目（CMIP6）中进行了大量实验。UKESM1是当今世界上最先进的地球系统模式，也是一个耦合的物理气候模式，包括(i)全球碳循环和动态植被，（ii）大气化学和气溶胶以及（iii）格陵兰和南极冰盖模式的相互作用处理。我们使用UKESM1运行了一个大型（19个成员）历史模拟集合（1850年至2015年），并根据CMIP6情景ip的7种不同的未来排放途径将其中一些模拟扩展到未来（2015年至2100年）。在这个扩展中，我们建议对UKESM1历史集合和场景ip预测套件进行详细分析。我们的目标是：(i)更好地理解驱动观测到的历史地球系统变化的因素，并评估UKESM1如何很好地代表这些变化；（ii）利用(i)的知识，分析UKESM1情景集成中模拟的地球系统变化，并将其与CMIP6多模式集成相结合，记录下未来一个世纪整个耦合地球系统的模拟变化范围。本分析的两个主要重点将是；(a)记录和对比不同全球平均变暖水平（如2℃或3℃）下的区域变化；(b)在可能的情况下，约束UKESM1模拟的驱动未来变化幅度的各种耦合反馈。此外，我们将继续为大型UKESM用户和模型开发社区提供支持，并将与(i)英国气候政策制定者和（ii）英国气候影响研究人员举行两次咨询研讨会。在这些研讨会上，我们将展示我们对预测未来地球系统变化的发现，并就英国地球系统建模如何最好地支持这两个群体的需求展开双向对话，在相互理解每个群体的需求和目标的基础上发展未来的合作。

Global climate change is one of the leading environmental threats facing mankind. To develop appropriate mitigation and adaptation strategies requires accurate projections of the future state of the Earth's climate. To address this, we develop and use Global Climate Models (GCMs) that describe the main physical processes in the coupled climate system. These models are integrated forwards in simulated time, from a pre-industrial period to present-day, forced by observed estimates of key greenhouse gases, aerosols and land-use. The models are then continued into the future forced by a range of greenhouse gas, aerosol and land-use scenarios. Each of the model future climates can then compared to the simulated present-day climates. This analysis results in an ensemble of climate change estimates that can be used to assess the socio-economic and ecological impacts of the simulated changes and aid in the development of mitigation and adaptation policies. GCMs have been further developed into Earth system models (ESMs), as we successfully did in the UKESM LTSM, where UKESM1 was developed from the coupled physical model, HadGEM3-GC3.1. A key difference between ESMs and GCMs is the former include an interactive description of the global carbon cycle supporting the analysis of both physical climate change and potential changes in the efficacy by which anthropogenic emitted CO2 is taken up by natural carbon reservoirs. A reduction in the uptake efficiency of Earth's natural carbon reservoirs may result in a larger fraction of emitted carbon dioxide remaining in the atmosphere to warm the planet. Accurate estimates of the future evolution of both the global climate system and the carbon cycle are therefore crucial for getting a clear picture of the future risks humanity faces, as well as for developing mitigation actions (that typically target the efficacy of carbon uptake) to keep global warming below dangerous levels. To address this need, we developed the 1st UK Earth system model (UKESM1) and ran it for a large suite of experiments in the 6th Coupled Model Intercomparison Project (CMIP6). UKESM1 is the most advanced Earth system model in the world today and as well as a coupled physical climate model, includes interactive treatment of (i) the global carbon cycle and dynamic vegetation, (ii) atmospheric chemistry and aerosols and (iii) models for the Greenland and Antarctic ice sheets. We have run a large (19 member) ensemble of historical simulations with UKESM1 (1850 to 2015) and extended a number of these into the future (2015 to 2100) following 7 different future emission pathways from CMIP6 scenarioMIP. In this extension, we propose a detailed analysis of the UKESM1 historical ensemble and the suite of scenarioMIP projections. Our aims are (i) to better understand what drives observed historical Earth system change and evaluate how well UKESM1 represents these changes, (ii) with the knowledge from (i), analyze simulated Earth system change in the UKESM1 scenarioMIP ensemble, combining this with the CMIP6 multi-model ensemble, to document the range of simulated changes across the coupled Earth system over the coming century. Two primary emphases in this analysis will be; (a) to document and contrast regional changes at different levels of global mean warming (e.g. 2C or 3C) and (b) where possible, to constrain the various coupled feedbacks simulated by UKESM1 that drive the magnitude of future change. In addition, we will continue to provide support to the large UKESM user and model development community and will hold two consultation workshops with (i) UK climate policymakers and (ii) UK climate impacts researchers. In these workshops we will present our findings on predicted future Earth system change and begin a two-way dialogue on how UK Earth system modeling can best support the needs of these two groups, developing future collaborations based on mutual understanding of each group's needs and goals.