The UK Earth system modelling project.

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，需要准确预测地球气候的未来状况。为了解决这一问题，研究界开发了全球气候模型(GCM)，描述了耦合气候系统中的主要物理过程。这些数学-计算机模型是在模拟时间内向前整合的，从前工业化时期(~1850年之前)到现在，受关键温室气体(如二氧化碳、甲烷、臭氧)、气溶胶和土地利用的观测估计所强迫。然后，这些模型继续进入模拟的未来，受一系列温室气体、气溶胶和土地使用情景的影响，这些情景代表了看似合理的未来社会经济发展路径。然后，将每个随时间演变的模型的未来气候与同一模型中的工业化前和现在的气候进行比较。这一分析产生了一套气候变化估计，这些估计与每一条应用的发展路径相联系，可用于评估潜在的社会经济和生态影响，并有助于制定气候变化缓解和适应政策。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。气候变化主要是由人类排放的二氧化碳推动的，二氧化碳将地球排放的辐射的一小部分困在大气中，使大气和地球表面变暖。气候系统中的各种反馈(例如，涉及水蒸气、云或海冰)可能会放大或抑制二氧化碳增加造成的直接变暖。人类排放的二氧化碳对气候变化的影响的一个关键决定因素是，排放的气体中有多少实际上留在了大气中，在那里它可以与地球排放的辐射相互作用。目前，人类排放的二氧化碳中约有50%留在大气中，其余50%被陆地生物圈和世界海洋以大致相同的方式吸收。越来越多的证据表明，这些天然碳库吸收人类排放的二氧化碳的效率可能会在未来发生变化，对地球系统中的二氧化碳浓度和引发的气候变化都很敏感。地球天然碳库吸收效率的降低将导致更大比例的二氧化碳排放留在大气中，从而对给定的二氧化碳累积排放量造成更大的气候变化(变暖)。为了满足模拟不断变化的全球气候以及碳循环对不断变化的气候和大气成分的响应的需要，我们正在开发第一个英国地球系统模型，该模型基于英国气象局开发的核心物理GCM HadGEM3。这一发展是NERC中心和气象局之间的一次重大合作，将大量核心研究和开发整合到一个单一的、世界领先的ESM中。这项提议旨在确保NERC的资金，以维持这种合作。该项目将支持第一个UKESM模型的最终开发和社区发布，以及将这些模型应用于在国际一级开展的一系列合作科学实验，以支持IPCC AR6。该项目的主要重点是评估UKESM1模型模拟的各种气候和生物地球化学过程及相互作用，目的是增加人们对用模型作出的未来预测的信心。该项目还将生成和分析一系列这样的预测，并向英国政府、企业和公众提供一套关于地球系统变化的强有力的估计。最后，该项目将启动UKESM模型第二版的长期开发，将于2023年发布。

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, the research community have developed Global Climate Models (GCMs) that describe the main physical processes in the coupled climate system. These mathematical-computer models are integrated forwards in simulated time, from a pre-industrial period(before ~1850) to present-day, forced by observed estimates of key greenhouse gases (e.g. carbon dioxide, methane, ozone), aerosols and land-use. The models are then continued into the simulated future forced by a range of greenhouse gas, aerosol and land-use scenarios representing plausible future socio-economic development pathways. Each of the time-evolving model future climates are then compared to the pre-industrial and present-day climates from the same model. This analysis results in an ensemble of climate change estimates, linked to each of the applied development pathways, that can be used to assess potential socio-economic and ecological impacts and aid in the development of climate change mitigation and adaptation policies.GCMs have recently been further developed into Earth system models (ESMs). A key difference between ESMs and GCMs is the former include an interactive description of the global carbon cycle. Climate change is primarily driven by human emissions of carbon dioxide which traps a fraction of the Earth's emitted radiation in the atmosphere, warming it and the Earth's surface. This direct warming from increasing carbon dioxide can be amplified or damped by various feedbacks in the climate system (e.g. involving water vapour, clouds or sea-ice). A key determinant of the climate change impact of human-emitted carbon dioxide is how much of the emitted gas actually stays in the atmosphere where it can interact with the Earth's emitted radiation. Presently, around 50% of the carbon dioxide emitted by humans stays in the atmosphere, the remaining 50% being taken up, in roughly equal measures, by the terrestrial biosphere and the world oceans. There is increasing evidence to suggest the efficiency of these natural carbon reservoirs in absorbing human-emitted carbon dioxide may change in the future, being sensitive to both the concentration of carbon dioxide in the Earth system and to the induced climate change. A reduction in the uptake efficiency of Earth's natural carbon reservoirs would result in a larger fraction of emitted carbon dioxide remaining in the atmosphere and thereby a larger climate change (warming) for a given cumulative emission of carbon dioxide.To address the need to simulate both the changing global climate and the carbon cycle response to a changing climate and changing atmospheric composition, we are developing the 1st UK Earth system model, based on the core physical GCM, HadGEM3, developed at the Met Office. This development is a major collaboration between NERC centres and the Met Office, integrating a large body of core research and development into a single, world-leading ESM. This proposal aims to secure the NERC funding to maintain this collaboration. The project will support the final development and community release of the 1st UKESM models, as well as application of these models to a range of collaborative science experiments carried out at the international level to support the IPCC AR6. The project has a major emphasis on evaluating the full range of climate and biogeochemical processes and interactions simulated by UKESM1 models with an aim to increase confidence in future projections made with the models. The project will also generate and analyse a suite of such projections and deliver a set of robust estimates of Earth system change to UK government, business and the public.Finally, the project will initiate long-term development of a 2nd version of the UKESM model, for release ~2023.