The role of oceans in climate asymmetries

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The oceans are responsible for a range of scientifically interesting and societally relevant asymmetries in Earth's climate. Moreover, the ocean's long timescales and diverse regional circulations impose strong constraints on the patterns of surface and subsurface warming under greenhouse-gas forcing. In turn, oceans mediate the rate and magnitude of global warming through (i) storage of anomalous heat at depth and (ii) the coupling between surface warming patterns and atmospheric radiative feedbacks, which governs the evolution of global climate sensitivity. Insights into the role of oceans in climate have come from idealized coupled global climate model (GCM) experiments wherein different ocean circulations and climates are induced by prescribing distinct continental geometries. This project is to examine the role of large scale oceanic circulation in the earth's climate system in simplified geometries and with cloud feedbacks. Different idealized continental configurations will be considered. This work improves upon previous efforts that have used ocean-only models or coupled models that did not include cloud-feedbacks. This work would support a female graduate student, an assistant professor to advise the research, and a part-time software engineer to assist in technical aspects of computing and modeling. The graduate student would gain valuable experience in teaching and communicating climate science. The idealized nature of results from this project would make them valuable additions to undergraduate and graduate courses. Tools developed for the purposes of designing idealized continental (or bathymetric) geometries in the coupled model will be made widely available to the community through both GitHub and, eventually, within NCAR's Community Earth System Model (CESM) idealized ocean model hierarchy.This project improves on previously idealized, coupled modeling framework in three key ways: (i) By employing state-of-the-art model components that, importantly, represent realistic cloud feedbacks which were previously neglected; (ii) By performing simulations with novel continental geometries and with varying planetary rotation rates; and (iii) By performing carbon dioxide forcing simulations with a range of background ocean circulation regimes induced by those distinct continental geometries. These model experiments are designed to answer key outstanding questions about the role of oceans in climate and climate change. The work will lead to improved understanding of the conditions by which large-scale ocean circulations arise and in turn govern: (i) large-scale asymmetries in climate; (ii) geographic patterns of climate change; and (iii) the rate and magnitude of global warming. In particular, it will provide deeper knowledge of the specific dynamics by which the oceans and atmosphere affect pole-to-equator temperature gradients; meridional heat transport and its partitioning between oceans and atmosphere; freshwater transport; tropical rainfall patterns; and localization of deep-water formation and meridional overturning. The work could also provide a physical theory for why GCMs predict increasing climate sensitivity under greenhouse-gas forcing, thus improving our understanding of one of the major uncertainties in climate projection. Evaluating the key role of clouds and cloud feedbacks in contributing to these features will be a focus throughout.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.