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Kerry Cook/UT Austin

Title: Influence of Atlantic SST thresholds on continental climates: Development and application of a coupled atmosphere/ocean/vegetation regional climate model

The research effort will produce a coupled atmosphere/ocean/vegetation regional climate model that can be adaptable to any region of interest and utilized at spatial resolutions much finer than current coupled GCMs for regional climate change studies and impact assessment. Also relevant for broader impacts is the use of the vegetation model, which allows us to “translate” climate change scenarios into changes in vegetation, making the results more directly meaningful to policy makers.

David Holland/Courant Institute NYU

Title: Modeling Abrupt Change in Global Sea Level Arising from Ocean – Ice-Sheet Interaction

A collaboration with the Los Alamos National Laboratory's IMPACTS science team, the project’s ultimate goal is to provide a robust, accurate prediction of future global sea level change, a feat that no fully-coupled climate model is currently capable of producing. This proposal seeks to advance that ultimate goal by developing, validating, and applying a regional model that can simulate the detailed processes involved in sealevel change due to ocean – ice-sheet interaction. Directly modeling ocean – ice-sheet processes in a fully-coupled global climate model is not a feasible activity given the near-complete absence of development of any such causal mechanism in these models to date. This proposal will advance the state-of-the-art in modeling of three key processes, either missing or underrepresented, in a coupled model. The identified processes are intrinsically coupled phenomenon between the ocean and the ice sheet. Each occurs at the floating extension of the ice sheet, i.e., on the ice shelf. The relevant ice shelf processes are basal melting, iceberg calving and grounding line migration.

Alexey Fedorov/Yale

Title: What controls the structure and stability of the ocean meridional overturning circulation: implications for abrupt climate change?

That a freshening and warming of surface waters in high latitudes can lead to a weakening or even a shutdown of the Atlantic Meridional Overturning Circulation (AMOC) has been a topic of many previous studies; the potential impacts of such a shut-down are most prominent over the northern Atlantic and western Europe, but felt in other parts of the globe as well. Yet, what controls the structure and overall stability of the AMOC remains a subject of debate. Here, we will systematically explore the role of several key factors that affect the AMOC structure and stability, including the wind forcing and the wind-driven circulation, ocean vertical diffusion, and the AMOC temporal variability.

Dennis Lettenmaier/UW Seattle

Title: Susceptibility of Colorado River basin to megadroughts in a warming climate

A collaboration with the Pacific Northwest National Laboratory's IMPACTS science team, this research outlines a plan that will address the central science question: "Will the Colorado River basin, and the U.S. Southwest more generally, transition to a permanent megadrought state over the next century, and what role will land atmosphere feedbacks play relative to remote climate forcings if such changes occur?"

Adam Schlosser/MIT and Jerry Melillo/Woods Hole Oceanographic Institution
Katey Walter/U Alaska Fairbanks
Qianlai Zhang/Purdue

Title: Quantifying Climate Feedbacks from Abrupt Changes in High-Latitude Trace-Gas Emissions

A collaboration with the Lawrence Berkeley National Laboratory's IMPACTS science team, the overall goal of this research is to quantify the potential for threshold changes in natural emission rates of trace gases, particularly methane and carbon dioxide, from pan-arctic terrestrial systems under the spectrum of anthropogenically forced climate warming, and the extent to which these emissions provide a strong feedback mechanism to global climate warming.

John Chiang/UC Berkeley

Title: Interhemispheric pattern in 20th century and future abrupt change in regional tropical rainfall

The overall project goal is to advance understanding of the “interhemispheric pattern” of global climate change that has been implicated in abrupt rainfall changes over the Sahel and other tropical locations over the 20th century, including origins, mechanisms, and future changes. A particular hypothesis we test is the potential role of radiative forcing over the subsidence regions associated with the Sahel and Indian monsoon rainfall. The main expected outcomes of this study are (i) Conclusively identifying the roles of natural and anthropogenic forcings in driving the interhemispheric pattern in the 20th century (ii) A mechanistic understanding of abrupt monsoon rainfall change over the Sahel in the 20th century resulting from the interhemispheric pattern; and (iii) An assessment of the occurrence of these changes in future climate scenarios.

Ping Chang/Texas A&M
Charles Jackson/UT Austin

Title: Searching for Atlantic Thermohaline Circulation Strength Threshold Leading to Abrupt Change of the African Monsoon

The overall goal of this research is to determine the likelihood that under global warming conditions the Atlantic thermohaline circulation (ATHC) threshold behavior will lead to an abrupt change of the African Monsoon.

Chris Hill/MIT
Peter Winsor/Woods Hole Oceanographic Institution

Title: Abrupt Climate Change and the Atlantic Meridional Overturning Circulation - sensitivity and non-linear response to Arctic/sub-Arctic freshwater pulses

We propose to undertake high-resolution forward and adjoint numerical modeling to examine the pathways of fresh-water pulses that impact Atlantic Meridional Overturning Circulation (AMOC) deep-water formation, on time-scales of years to multiple decades. The proposed work will yield a clearer picture of how the real planetary AMOC, a key piece of the global ocean thermohaline circulation (THC), could respond to future fresh-water events arising from climate change.

Xu Liang/Univ Pittsburgh

Title: The Role of Vegetation, Surface, and Subsurface Processes on Mega Drought and Its Implications to Climate Change

This is a collaboration with the Pacific Northwest National Laboratory's IMPACTS team addressing mega-droughts.  Drought is a recurrent feature in many parts of the U.S. Multi-year droughts, in particular, are very devastating and costly. We hypothesize that plants modulate droughts at the initial stage through hydraulic redistribution by roots, root growth, and changes in water storage to tap moisture in the deeper soil layers or groundwater table, and stomatal response to maintain transpiration. However, when the groundwater table falls below a critical level, droughts can be intensified and sustained as plants and surface processes become decoupled to subsurface processes such that reduced surface soil moisture and plants transpiration accelerate the drying through land-atmosphere interactions. This process can also trigger a rapid, drought-induced die-off of vegetation which can lead to shifts in vegetation distribution at regional scale, which can, in combination with the feedbacks effects and other factors, result in large impacts on and abrupt change in the regional climate. To test this hypothesis, we propose model developments to include the effects of hydraulic redistribution and plant storage in the transpiration process, and integrate these effects with a stomatal conductance representation that explicitly considers the dependence of the net rate of photosynthesis and water use. Our study will focus on the mid-latitude regions of the U.S to investigate the processes and mechanisms that lead potentially the abrupt transition to mega droughts and the consequences of such droughts on the land-atmospheric system.

Zhengyu Liu/UW Madison
Bette Otto-Bliesner/UCAR NCAR

Title: Simulating and Understanding Abrupt Climate-Ecosystem Changes During Holocene with NCAR-CCSM3

Abrupt climate change is emerging as one of the most urgent environmental issues facing our society. However, our understanding and predictive capability of abrupt changes remain extremely limited. Here, we propose to study abrupt climate change by focusing on the two greatest abrupt environmental change events in the last 10,000 years: the abrupt collapse of the North African monsoon-ecosystem in the mid-Holocene, and the abrupt cooling event in the Pan-Atlantic ocean-atmosphere system at 8200 years ago. These two major events provide a unique validation target for our modeling study because they have large and clear signals; they are also relevant to abrupt changes in the future because they have background climatology comparable with present and include fast feedbacks that might be realized with future anthropogenic change.