Andrew G. Slater, Ph.D. - US grants

This project will develop an Arctic System Reanalysis (ASR). The ASR, which can be viewed as a blend of modeling and observations, will provide a high resolution description in space (20 km) and time (3 h) of the atmosphere-sea ice-land surface system of the Arctic. The ASR will ingest historical data streams along with measurements of the physical components of the Arctic Observing Network being developed as part of the IPY. Gridded fields from the ASR, such as temperature, radiation and winds, will also serve as drivers for coupled ice-ocean, land surface and other models, and will offer a focal point for coordinated model inter-comparison efforts. The ASR will permit reconstructions of the Arctic system's state, thereby serving as a state-of-the-art synthesis tool for assessing Arctic climate variability and monitoring Arctic change. The ASR will also shape the legacy observing network of the IPY by providing a vehicle for observing system sensitivity studies. The first generation ASR as outlined here will span the years 2000-2010.

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). The primary goal of this project is to investigate the mechanisms underlying the seasonal response of the climate system to Arctic sea ice loss within the context of anthropogenic climate change. This research will utilize the NCAR Community Climate System Model, version 4 (CCSM4), which is a fully coupled global atmosphere-ocean-cryosphere-land model with terrestrial and oceanic carbon-nitrogen cycling capabilities. The overarching goal of this proposed effort is to investigate the relative roles of sea ice loss versus rising greenhouse gases for changes in the seasonal succession and timing of Arctic processes. This will involve research designed to assess the influence of seasonal sea ice loss on aspects of the marine, terrestrial, and atmospheric systems, with a particular emphasis on the seasonal dependence of the responses. This work will include a series of targeted sensitivity integrations to isolate processes of interest. These experiments will be evaluated within the context of available observations. This project will also assess the integrated effects of these various processes and how they in turn feed back onto the seasonality of Arctic sea ice change. Current and projected changes in the Arctic system have repercussions for the global climate system, Arctic wildlife, and socio-economic activities in the region. Improving our understanding and modeling of the factors affecting the seasonal timing and succession of processes within the Arctic system will allow for improved Arctic and global system predictability. This has a direct impact on the ability of society to anticipate, mitigate, and adapt to future change.

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

The Arctic system is strongly defined by its seasonality. The extreme annual cycle of solar radiation, interactions between the Arctic and lower latitudes, within-Arctic interactions between the land, ocean, and atmosphere, and the energetics of freeze and thaw, combine to lend a complexity and richness to Arctic seasonality not seen elsewhere on the planet. This seasonality is changing. Summer sea ice extent is declining, attended by strong autumn rises in air temperature over the Arctic Ocean. Active layer freeze-up in Siberia is occurring later in the winter. These and other emerging changes will become more prominent in coming decades, with impacts promising to cascade through the physical, chemical, biological, and socio-economic components of the system.

This research will identify the dominant climate forcings, feedbacks, and component linkages driving change in Arctic system seasonality, and they will shape the evolution of the system through the 21st century. This will require consideration of changes in global radiative forcing, energy and mass transports from lower latitudes into the Arctic, and between the land, ocean, and atmosphere within the Arctic, and how these influence the Arctic?s physical, chemical, and biological processes. A framework of passive versus active controls will help to organize the investigations. A passive control is the control by background warming. An example is how Arctic warming will lead to shorter seasonal duration of snow cover. An active control refers to altered seasonality driven by changes in energy or mass transports into the Arctic from lower latitudes or within the Arctic itself. An example is how reduced autumn sea-ice extent leads to warming over the ocean, which then, through regional atmospheric transport, may lead to warming over adjacent land. Changes in seasonality will likely often reflect both passive and active controls. Diagnostics such as seasonal anomaly structures, defined as the seasonal cycle of a state variable for a given year or years relative to the long-term climatology, will be used to evaluate how seasonality in different system elements has evolved through the instrumental record. These observational analyses will guide modeling experiments to examine the sensitivity of state variables to active and passive controls and how changing seasonality will shape the future of the system.

The Arctic is currently experiencing rapid environmental change, for example, widespread permafrost thaw and associated thermokarst initiation, changes in lake distribution, shifts in vegetation community composition, as well as changes in a host of other ecosystem processes. Threshold and non-linear responses associated with phase change between ice and water leave the Arctic particularly susceptible to swift and disruptive change. Realization of the scope of change, in conjunction with its pace, has spawned  concern that the massive and, until recently, effectively dormant soil carbon pools stored in permafrost-affected and peatland soils may be more vulnerable than previously thought. The fate of the Arctic carbon cycle is fundamentally governed by present and future soil hydrologic states.  There is an urgent need for the scientific community to be able to assess and quantify whether or not this carbon is an ?Arctic carbon time bomb?, as it is sometimes colloquially referred to, or if other biogeophysical and biogeochemical feedbacks will restrict or mitigate a substantial carbon release as permafrost thaws. Comprehensive Earth System Models (ESMs), such as the Community Earth System Model (CESM), are required to assess the integrated Arctic and global response to terrestrial Arctic change.  Though recent advances in the land model of CESM have been made with respect to the representation of permafrost, biogeochemical cycles, and Arctic vegetation succession, the current representation of cold region hydrology is inadequate to permit a holistic study of the Arctic permafrost carbon problem.  To address this limitation, we propose a targeted effort to improve Arctic terrestrial hydrological processes in the CESM and to use the resulting model to assess recent and future decadal-scale Arctic hydrology change.  The successful completion of this project will provide the foundation for a thorough evaluation of the Arctic terrestrial biogeochemical feedbacks.

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.