Uncertainty for America’s Coasts: The Future of the Atlantic Meridional Overturning Circulation

EPA Grant Number: FP917807
Title: Uncertainty for America’s Coasts: The Future of the Atlantic Meridional Overturning Circulation
Investigators: Beadling, Rebecca Lynn
Institution: University of Arizona
EPA Project Officer: Lee, Sonja
Project Period: September 1, 2015 through August 31, 2018
Project Amount: $132,000
RFA: STAR Graduate Fellowships (2015) RFA Text |  Recipients Lists
Research Category: Academic Fellowships

Objective:

Observations of the Atlantic Meridional Overturning Circulation (AMOC) available since 2004 reveal an overall decline in strength, and future projections of AMOC strength calculated by the latest Earth System Models all project a significant decline in AMOC strength under increased greenhouse gas concentrations. None of these future projections include the potential impacts of the melting of the Greenland Ice Sheet on a further AMOC weakening - despite this large source of freshwater being located directly next to the AMOC's convection sites. This research combines the results from Earth System Model experiments with observations to advance our understanding of how AMOC will evolve into the future as the climate continues to warm, including how AMOC will respond to the meltwater from the Greenland Ice Sheet.

Approach:

To address the uncertainty of the role that the Greenland Ice Sheet will play in a further weakening of AMOC, data generated from experiments that I have designed and carried out using the Geophysical Fluid Dynamics Laboratory's Earth System Model, ESM2Mb, forced with realistic projections of melt water from the Greenland Ice Sheet will be analyzed. The results of these melt water experiments will be compared to the same experiments without the inclusion of melt water forcing as well as to the same experiments carried out using different Earth System Models. This will be a continuation of my contribution towards the AMOC Model Intercomparison Project (AMOCMIP), a community effort to address this uncertainty. To understand how AMOC will evolve into the future, it is critical to understand how AMOC is simulated in Earth System Models compared to observations. To do this, I will analyze how each component of the AMOC is simulated in Earth System Models compared to observations. This will provide critical information for improvement of AMOC simulations in Earth System Models, advancing our abilities to make more realistic projections of future AMOC behavior.

Expected Results:

All Earth System Models used in the latest Intergovernmental Panel on Climate Change (IPCC) report project a significant weakening of the AMOC by the end of the 21st century, with major global impacts. None of these projections of future AMOC strength consider the impacts of the melting of the Greenland Ice Sheet (GIS) despite this large source of freshwater being located directly next to the AMOC’s convection sites. Observations show an increase in the melting of the GIS since the early 20th century with a significant acceleration over the past decade. We expect that inclusion of realistic projections of freshwater from the Greenland Ice Sheet will result in an additional decrease in AMOC strength in GFDL's ESM2Mb as well as in the other models involved in this study. We expect the response to the freshwater from the Greenland Ice Sheet will differ widely between models used due to different configurations and sensitivity to the freshwater forcing; differences which we will study in detail to understand the mechanism by which the freshwater forcing impacts AMOC in each model. We expect that analysis of differences between model response to the forcing as well as differences between how AMOC is simulated in each model compared to observations will provide critical information to allow for model improvement and more realistic AMOC projections.

Supplemental Keywords:

Greenland, AMOC, Climate, Earth System Model