Climate feedbacks from wetlands and permafrost thaw in a warming world (CLIFFTOP)

二氧化碳和甲烷是导致全球变暖和气候变化的最重要的长寿温室气体。这两种气体是全球碳循环的主要组成部分，从自然和人类活动中以各种方式加入和清除到大气中。湿地是甲烷的最大自然来源，在全球变暖的情况下，湿地的甲烷排放量预计会增加。此外，在北部高纬度地区，大量的碳储存在冻土或永久冻土中。极地地区变暖的速度比地球其他地区更快。随着这些土壤变暖，导致永久冻土融化，储存的碳可以随着时间的推移被微生物活动转化，以二氧化碳或甲烷的形式释放到大气中，导致进一步变暖，从而产生积极的反馈。与景观变化相结合，这可能导致新的湿地的形成，导致甲烷的进一步排放。因此，湿地和永久冻土融化是重要的生物地球化学过程，需要包括在地球气候模型中。通过纳入气候，或者现在是地球系统，模型将考虑湿地和永久冻土融化对物理气候系统产生的反馈(例如，关于未来温度变化的反馈)。在2015年达成国际气候协议，将未来气温上升控制在比工业化前水平低1.5-2摄氏度之后，迫切需要量化湿地和永久冻土融化的这种贡献，因为如果全球气温要稳定下来，这将限制人类活动(如化石燃料燃烧)释放的温室气体的累积排放量。在这项研究中，我们将使用英国社区最先进的陆地表面模型，英国联合陆地环境模拟器(Jules)来模拟湿地和永久冻土融化。我们计划有针对性地开发陆地-地表模型，以增强其以更一致和更综合的方式考虑湿地、永久冻土融化、甲烷和二氧化碳排放的能力。在这项工作中，我们将使用Jules的这个改进版本和一个简化但健壮的气候模拟器Imogen。Imogen复制了一系列更复杂和资源密集型的气候和地球系统模型的行为，这些模型对IPC最新的气候变化评估做出了贡献。我们将使用Jules-Imogen模拟系统进行模型运行，(A)评估许多气候模型中未包括的北极碳排放的影响，(B)量化相应的气候反馈以及这些额外排放对1.5或2摄氏度气候稳定所允许的人类排放的影响。这项拟议的研究将为支持《巴黎协定》中做出的承诺提供重要证据，即加强全球对气候变化威胁的反应……并努力将气温上升控制在比工业化前水平高1.5摄氏度的水平。这项工作的成果将包括：*发表在科学文献中的论文，这些论文将被纳入IPCC对IPCC的特别评估*对大气模型界有价值的当今和未来条件的湿地甲烷排放数据集。该项目与我们的项目合作伙伴英国气象局正在进行的工作相联系，并将对其进行补充。

Carbon dioxide and methane are the most important long-lived greenhouse gases causing global warming and climate change. These two gases, which are the major components of the global carbon cycle, are added to and removed from the atmosphere in a wide range of ways, from both natural and human activities. Wetlands are the largest natural source of methane and methane emissions from wetlands are expected to increase in a warming world. Further, in high northern latitudes, large amounts of carbon are stored in frozen soils or permafrost. The polar regions are warming faster than other parts of the Earth. As these soils warm causing the permafrost to thaw, the stored carbon can be converted by microbial activity over time and released to the atmosphere as carbon dioxide or methane, leading to further warming and hence a positive feedback. Combined with landscape changes, this may lead to the formation of new wetlands resulting in further emissions of methane.Wetlands and permafrost thaw are therefore important biogeochemical processes that need to be included in models of the Earth's climate. Through their inclusion, climate, or now Earth System, models will then account for the feedbacks that wetlands and permafrost thaw produce on the physical climate system (e.g., on future temperature changes). Following the international climate agreement in 2015 to limit future temperature rises to less than 1.5-2 degrees centigrade above pre-industrial levels, there is an urgent need to quantify this contribution of wetlands and permafrost thaw as this will constrain the accumulated emissions of greenhouse gases that can be released from human activities such as fossil fuel combustion if global temperatures are to be stabilised.In this study, we will use the UK community state-of-the-art land surface model, the Joint UK Land Environment Simulator (JULES) to model wetlands and permafrost thaw. We plan targeted development of the land-surface model to enhance its capability for considering wetlands, permafrost thaw, methane and carbon dioxide emissions in a more consistent and integrated manner. For this work, we will use this improved version of JULES with a simplified but robust climate emulator, IMOGEN. IMOGEN replicates the behaviour of a wide range of more complex and resource intensive climate and Earth System models that contributed to the latest climate change assessment of the IPCC.We will undertake model runs with the JULES-IMOGEN modelling system (a) to assess the impact of Arctic carbon releases that are not included in many climate models, (b) to quantify the corresponding climate feedbacks and the impact of these additional emissions on allowed human emissions for 1.5 or 2 degree C climate stabilisations. The research proposed will provide important evidence to support the commitments made in the Paris Agreement to 'strengthen the global response to the threat of climate change.... and to pursue efforts to limit the temperature increase to 1.5 degree C above pre-industrial levels'.The outputs of the work will include:* papers for publication in the scientific literature, which will be included in the special IPCC assessment of the IPCC* wetland methane emission datasets for current day and future conditions that will be of value for the atmospheric modelling communityThe project links to and will complement ongoing work at the Met Office, our project partner, for the UK government.