Collaborative Research:The Climatic Role of Permafrost- As permafrost thaws, could a weakening terrestrial freezer and an increasingly leaky bathplug amplify Arctic climate change?

北极正在经历快速的环境变化，从海冰面积的减少到永久冻土的变暖，再到冰盖和冰川的融化和质量损失。重要的是，我们必须从根本上理解北极-S物理系统变化的驱动因素、影响和反馈，以及它们与北极和全球气候的关系。近年来，作为气候变化的诊断指标，永久冻土的潜在融化受到了极大的关注，但我们仍然不完全了解永久冻土在气候系统中的物理作用。永久冻土独特的物理属性对气候系统的各个方面施加了特殊的限制。例如，每年地面和地面中的水的冻结和融化通过消耗和释放潜热提供了一种季节性的减震机制。在更长的时间尺度上，较深的永久冻土层中富含冰冷的层在达到等温条件并上升到冰点以上之前，可以吸收相当数量的能量。从本质上讲，永久冻土充当了陆地地下冰柜的角色。多年冻土中的冰基质抑制了排水，从而导致近地表土壤饱和，并在活动层的底部出现了栖息地下水位和富冰瞬变层等现象。在某些方面，永久冻土可以被认为是活动层底部的浴缸塞子，导致活动层浴缸季节性地注满(通常是融雪水)。这些过程的存在、季节性和空间发生预计都将发生变化，但其影响仍未得到诊断。直到最近，气候或地球系统模型还没有包含足够的过程表示，以便能够调查土地-永冻土-大气-气候耦合系统。社区地球系统模式(CESM)及其陆地部分的模式能力社区陆地模式(CLM)近年来已经有了很大的进步，现在可以有意义地研究永久冻土在物理气候系统中的作用，无论是在目前的气候中，还是在可能的未来冻土少得多的情况下。为了了解永久冻土对现在和未来气候轨迹的贡献，该项目将利用最新版本的CESM-CLM进行一系列有针对性的模式实验。研究人员将寻求这些问题的答案：作为陆地冻土，永久冻土是如何控制的？还有？浴缸塞子？对北极气候施加影响？多年冻土的流失将如何反馈到北极气候变化的幅度、季节性或速度？我们将通过离线和耦合模拟进行数值实验，人工操纵多年冻土对气候系统的各种影响，以阐明目前永久冻土对气候系统的作用以及它的损失如何反馈到气候变化。这项研究的学术价值始于对北极气候资源管理S能力的评估。CLM模型被更广泛的科学界广泛使用。通过一系列实验，他们希望了解永久冻土在气候系统中的机械作用，以及这些机制将如何影响整个北极变化的轨迹。这项工作的更广泛的影响有几个。了解永久冻土对气候的长期影响可以建立智力资本，帮助进行从季节到十年的预测，并反馈到预测。北极变化既阻碍又鼓励社会经济发展，因此全系统的了解将有助于有效和负责任地利用区域资源。通过研究生的支持，该项目将为下一代研究人员做出贡献，并提高科学素养，因为学生将接触到气候建模的尖端技术，并发展分析技能，这些技能也可以转化为经济的许多部门。

The Arctic is experiencing rapid environmental change ranging from diminishing sea ice extent, to warming permafrost, to melting and mass loss on ice sheets and glaciers. It is important that we advance our fundamental understanding of the drivers, impacts, and feedbacks of changes in the Arctic?s physical system and how they relate to Arctic and global climate.The potential thaw of permafrost has received much attention in recent years as a diagnostic measure of climate change, yet we still do not fully understand the physical role that permafrost plays in the climate system. The unique physical attributes of permafrost impose particular constraints upon aspects of the climate system. For example, annual freezing and thawing of the ground and water in the ground provides a seasonal damping mechanism through the consumption and release of latent heat. On longer timescales, cold ice-rich layers of deeper permafrost can draw in considerable amounts of energy before breeching an isothermal condition and rising above the freezing point. In essence, permafrost acts as a terrestrial subsurface freezer. The ice matrix in permafrost soils inhibits drainage, which leads to saturated near-surface soils and phenomena such as a perched water table and an ice-rich transient layer at the base of the active layer. Permafrost can in some respects be considered as a bathplug at the base of the active layer that causes the active layer bathtub to fill (often with snowmelt water) seasonally. The existence of such processes, their seasonality and spatial occurrence are all expected to change, but the impacts remain undiagnosed. Until recently, climate or Earth system models have not contained sufficient process representation to allow investigation into the coupled land-permafrost-atmosphere- climate system. Model capabilities in the Community Earth System Model (CESM) and its terrestrial component the Community Land Model (CLM) have advanced considerably in recent years to the level that the role of permafrost on the physical climate system, in both the present climate and in a possible future with much less permafrost, can now be meaningfully investigated.To understand the contribution of permafrost to present and future climate trajectories, this project will conduct a series of targeted model experiments with the latest version of CESM-CLM. The researchers will seek answers to the questions: What control does permafrost, as a terrestrial ?freezer? and ?bathplug,? exert on Arctic climate? and How will a loss of permafrost feed back onto the amplitude, seasonality, or rate of Arctic climate change?Numerical experiments will be conducted in both off-line and coupled simulations with various influences of permafrost on the climate system artificially manipulated to illuminate the present-day role of permafrost on the climate system and how its loss can feedback onto climate change.The intellectual merit of the research begins with an evaluation of CLM?s capabilities in the Arctic. The CLM model is used extensively by the broader science community. Through a series of experiments they expect to gain an understanding of the mechanistic role of permafrost within the climate system and how those mechanisms will influence the trajectory of overall Arctic change. The broader impacts of the work are several. Understanding the longer-term impacts of permafrost on the climate builds intellectual capital that can aid with seasonal to decadal prediction with feedbacks to forecasting. Arctic change both hinders and encourages socio-economic development, thus system-wide understanding will aid efficient and responsible use of regional resources. Through the support of a graduate student the project will contribute to the next generation of researchers and improve scientific literacy, as the student is exposed to the cutting edge of climate modeling and develops analytic skills that can also translate to numerous sectors of the economy.