Nerem R. Steven

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R. Steven

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  • Article
    Origin of interannual variability in global mean sea level
    (National Academy of Sciences, 2020-06-08) Hamlington, Benjamin D. ; Piecuch, Christopher G. ; Reager, John T. ; Chandanpurkar, Hrishikesh A. ; Frederikse, Thomas ; Nerem, R. Steven ; Fasullo, John T. ; Cheon, Se-Hyeon
    The two dominant drivers of the global mean sea level (GMSL) variability at interannual timescales are steric changes due to changes in ocean heat content and barystatic changes due to the exchange of water mass between land and ocean. With Gravity Recovery and Climate Experiment (GRACE) satellites and Argo profiling floats, it has been possible to measure the relative steric and barystatic contributions to GMSL since 2004. While efforts to “close the GMSL budget” with satellite altimetry and other observing systems have been largely successful with regards to trends, the short time period covered by these records prohibits a full understanding of the drivers of interannual to decadal variability in GMSL. One particular area of focus is the link between variations in the El Niño−Southern Oscillation (ENSO) and GMSL. Recent literature disagrees on the relative importance of steric and barystatic contributions to interannual to decadal variability in GMSL. Here, we use a multivariate data analysis technique to estimate variability in barystatic and steric contributions to GMSL back to 1982. These independent estimates explain most of the observed interannual variability in satellite altimeter-measured GMSL. Both processes, which are highly correlated with ENSO variations, contribute about equally to observed interannual GMSL variability. A theoretical scaling analysis corroborates the observational results. The improved understanding of the origins of interannual variability in GMSL has important implications for our understanding of long-term trends in sea level, the hydrological cycle, and the planet’s radiation imbalance.
  • Article
    Understanding of contemporary regional sea-level change and the implications for the future
    (American Geophysical Union, 2020-04-17) Hamlington, Benjamin D. ; Gardner, Alex S. ; Ivins, Erik ; Lenaerts, Jan T. M. ; Reager, John T. ; Trossman, David S. ; Zaron, Edward D. ; Adhikari, Surendra ; Arendt, Anthony ; Aschwanden, Andy ; Beckley, Brian D. ; Bekaert, David P. S. ; Blewitt, Geoffrey ; Caron, Lambert ; Chambers, Don P. ; Chandanpurkar, Hrishikesh A. ; Christianson, Knut ; Csatho, Beata ; Cullather, Richard I. ; DeConto, Robert M. ; Fasullo, John T. ; Frederikse, Thomas ; Freymueller, Jeffrey T. ; Gilford, Daniel M. ; Girotto, Manuela ; Hammond, William C. ; Hock, Regine ; Holschuh, Nicholas ; Kopp, Robert E. ; Landerer, Felix ; Larour, Eric ; Menemenlis, Dimitris ; Merrifield, Mark ; Mitrovica, Jerry X. ; Nerem, R. Steven ; Nias, Isabel J. ; Nieves, Veronica ; Nowicki, Sophie ; Pangaluru, Kishore ; Piecuch, Christopher G. ; Ray, Richard D. ; Rounce, David R. ; Schlegel, Nicole‐Jeanne ; Seroussi, Helene ; Shirzaei, Manoochehr ; Sweet, William V. ; Velicogna, Isabella ; Vinogradova, Nadya ; Wahl, Thomas ; Wiese, David N. ; Willis, Michael J.
    Global sea level provides an important indicator of the state of the warming climate, but changes in regional sea level are most relevant for coastal communities around the world. With improvements to the sea‐level observing system, the knowledge of regional sea‐level change has advanced dramatically in recent years. Satellite measurements coupled with in situ observations have allowed for comprehensive study and improved understanding of the diverse set of drivers that lead to variations in sea level in space and time. Despite the advances, gaps in the understanding of contemporary sea‐level change remain and inhibit the ability to predict how the relevant processes may lead to future change. These gaps arise in part due to the complexity of the linkages between the drivers of sea‐level change. Here we review the individual processes which lead to sea‐level change and then describe how they combine and vary regionally. The intent of the paper is to provide an overview of the current state of understanding of the processes that cause regional sea‐level change and to identify and discuss limitations and uncertainty in our understanding of these processes. Areas where the lack of understanding or gaps in knowledge inhibit the ability to provide the needed information for comprehensive planning efforts are of particular focus. Finally, a goal of this paper is to highlight the role of the expanded sea‐level observation network—particularly as related to satellite observations—in the improved scientific understanding of the contributors to regional sea‐level change.