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，从海冰范围缩小到永久冻土变暖，再到冰盖和冰川融化和质量损失。重要的是，我们必须加深对北极物理系统变化的驱动因素、影响和反馈的基本了解，以及它们与北极和全球气候的关系。近年来，永久冻土的潜在融化作为气候变化的诊断指标受到了广泛关注，但我们仍然没有完全了解永久冻土在气候系统中所发挥的物理作用。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，每年地面和地下水的冻结和融化通过潜热的消耗和释放提供了季节性阻尼机制。在较长的时间尺度上，较深的永久冻土层中寒冷且富含冰的层可以在突破等温条件并升至冰点以上之前吸收大量能量。从本质上讲，永久冻土就像陆地的地下冷冻库。永久冻土中的冰基质会抑制排水，导致近地表土壤饱和，并出现地下水位停滞和活动层底部富含冰的过渡层等现象。在某些方面，永久冻土可以被视为活动层底部的浴塞，导致活动层浴缸季节性地充满（通常充满融雪水）。这些过程的存在、其季节性和空间发生都预计会发生变化，但其影响仍未确定。直到最近，气候或地球系统模型还没有包含足够的过程表征来研究耦合的土地-永久冻土-大气-气候系统。近年来，社区地球系统模型（CESM）及其陆地组成部分社区土地模型（CLM）的模型能力取得了相当大的进步，现在可以有意义地研究永久冻土对物理气候系统的作用，无论是在当前的气候中还是在永久冻土更少的未来。为了了解永久冻土对当前和未来气候轨迹的贡献，该项目将使用最新版本的CESM-CLM进行一系列有针对性的模型实验。研究人员将寻求以下问题的答案：永久冻土作为陆地“冰库”有何控制作用？和？浴缸插头，？对北极气候有何影响？永久冻土的丧失将如何反馈到北极气候变化的幅度、季节性或速率？将在离线和耦合模拟中进行数值实验，人工操纵永久冻土对气候系统的各种影响，以阐明永久冻土目前对气候系统的作用以及其丧失如何反馈到气候变化。这项研究的智力价值始于对 CLM 在北极的能力的评估。 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制作用，以及这些机制将如何影响北极整体变化的轨迹。这项工作的更广泛影响有几个。了解永久冻土对气候的长期影响可以建立智力资本，可以帮助进行季节到十年的预测，并提供预测反馈。北极变化既阻碍又鼓励社会经济发展，因此全系统的理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，因为学生将接触最前沿的气候模型并发展分析技能，这些技能也可以转化为众多经济部门。

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.