Impact of the Atlantic Meridional Overturning Circulation on Surface Conditions: Isolating the Effects of Feedbacks and Mean-state Overturning Strength

This project investigates how a major ocean current system, the Atlantic Meridional Overturning Circulation (AMOC), influences near-term changes in surface atmospheric conditions over the globe. Today’s earth system models (ESMs) yield widely conflicting results for both present-day AMOC strength and how much AMOC will slow in the future. This project will assess how both the present-day strength of the AMOC and the future decline of the AMOC influence atmospheric and surface features, such as cloud cover and sea ice, and how these changes influence subsequent temperature change. Improving our understanding of how ocean circulation impacts the rest of the earth enables more accurate long-term predictions and projections from ESMs. The project will also engage with local communities through public outreach and community science initiatives, and provide training for the next generation of scientists. The project addresses two key questions: (1) What are the mechanisms by which AMOC decline impacts radiative feedbacks, including interactions between different radiative feedbacks and interactions between the feedbacks and the atmospheric and oceanic circulations? (2) How does the mean-state AMOC impact uncertainty in future temperature change? These questions will be addressed using two sets of experiments in the Community Earth System Model (CESM), a state-of-the-art ESM. The first set of experiments will apply feedback locking to capture the full effects of AMOC-induced changes in cloud feedbacks and in the wind-evaporation-sea-surface-temperature feedback on near-future warming. This will test the hypothesis that AMOC-induced changes in the North Atlantic shortwave cloud feedback influence local surface warming in part by modifying other feedbacks, with additional, nonlocal effects on surface warming via changes in atmospheric and ocean heat transport. The second set of experiments will isolate the effects of the AMOC on mean-state clouds and sea ice, as well as the sensitivity of future warming to these mean-state effects. This will test the hypothesis that the AMOC's mean state impacts surface warming by changing climatological low cloud cover and sea-ice area, which influence the shortwave cloud and ice-albedo feedbacks. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria. NSF Award ID: 2538364 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Nicholas Lutsko | Institution: University of California-San Diego Scripps Inst of Oceanography, LA JOLLA, CA | Award Amount: $835,425 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2538364 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2538364.html