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