Kemp Andrew C.

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Kemp
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Andrew C.
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  • Preprint
    Increased threat of tropical cyclones and coastal flooding to New York City during the anthropogenic era
    ( 2015-08) Reed, Andra J. ; Mann, Michael E. ; Emanuel, Kerry A. ; Lin, Ning ; Horton, Benjamin P. ; Kemp, Andrew C. ; Donnelly, Jeffrey P.
    In a changing climate, future inundation of the United States’ Atlantic coast will depend on both storm surges during tropical cyclones and the rising relative sea-levels on which those surges occur. However, the observational record of tropical cyclones in the North Atlantic basin is too short (AD 1851-present) to accurately assess long-term trends in storm activity. To overcome this limitation, we use proxy sealevel records, and downscale three CMIP5 models to generate large synthetic tropical cyclone data sets for the North Atlantic basin; driving climate conditions span from AD 850 to AD 2005. We compare preanthropogenic era (AD 850 – AD 1800) and anthropogenic era (AD 1970 – AD 2005) storm-surge model results for New York City, exposing links between increased rates of sea-level rise and storm flood heights. We find that mean flood heights increased by ~1.24 m (due mainly to sea level rise) from ~AD 850 to the anthropogenic era, a result that is significant at the 99% confidence level. Additionally, changes in tropical cyclone characteristics have led to increases in the extremes of the types of storms that create the largest storm surges for New York City. As a result, flood risk has greatly increased for the region; for example, the 500 year return period for a ~2.25 m flood height during the preanthropogenic era has decreased to ~24.4 years in the anthropogenic era. Our results indicate the impacts of climate change on coastal inundation, and call for advanced risk management strategies.
  • Article
    River-discharge effects on United States Atlantic and Gulf coast sea-level changes
    (National Academy of Sciences, 2018-07-09) Piecuch, Christopher G. ; Bittermann, Klaus ; Kemp, Andrew C. ; Ponte, Rui Vasques de Melo ; Little, Christopher M. ; Engelhart, Simon E. ; Lentz, Steven J.
    Identifying physical processes responsible for historical coastal sea-level changes is important for anticipating future impacts. Recent studies sought to understand the drivers of interannual to multidecadal sea-level changes on the United States Atlantic and Gulf coasts. Ocean dynamics, terrestrial water storage, vertical land motion, and melting of land ice were highlighted as important mechanisms of sea-level change along this densely populated coast on these time scales. While known to exert an important control on coastal ocean circulation, variable river discharge has been absent from recent discussions of drivers of sea-level change. We update calculations from the 1970s, comparing annual river-discharge and coastal sea-level data along the Gulf of Maine, Mid-Atlantic Bight, South Atlantic Bight, and Gulf of Mexico during 1910–2017. We show that river-discharge and sea-level changes are significantly correlated (p<0.01), such that sea level rises between 0.01 and 0.08 cm for a 1 km3 annual river-discharge increase, depending on region. We formulate a theory that describes the relation between river-discharge and halosteric sea-level changes (i.e., changes in sea level related to salinity) as a function of river discharge, Earth’s rotation, and density stratification. This theory correctly predicts the order of observed increment sea-level change per unit river-discharge anomaly, suggesting a causal relation. Our results have implications for remote sensing, climate modeling, interpreting Common Era proxy sea-level reconstructions, and projecting coastal flood risk.
  • Preprint
    Origin of spatial variation in US East Coast sea-level trends during 1900-2017
    (Nature Research, 2018-12-18) Piecuch, Christopher G. ; Huybers, Peter ; Hay, Carling C. ; Kemp, Andrew C. ; Little, Christopher M. ; Mitrovica, Jerry X. ; Ponte, Rui M. ; Tingley, Martin P.
    Identifying the causes of historical trends in relative sea level—the height of the sea surface relative to Earth’s crust—is a prerequisite for predicting future changes. Rates of change along the U.S. East Coast during the last century were spatially variable, and relative sea level rose faster along the Mid-Atlantic Bight than the South Atlantic Bight and Gulf of Maine. Past studies suggest that Earth’s ongoing response to the last deglaciation1–5, surface redistribution of ice and water 5–9, and changes in ocean circulation9–13 contributed importantly to this large-scale spatial pattern. Here we analyze instrumental data14, 15 and proxy reconstructions4, 12 using probabilistic methods16–18 to show that vertical motions of Earth’s crust exerted the dominant control on regional spatial differences in relative sea level trends along the U.S. East Coast during 1900–2017, explaining a majority of the large-scale spatial variance. Rates of coastal subsidence caused by ongoing relaxation of the peripheral forebulge associated with the last deglaciation are strongest near North Carolina,Maryland, and Virginia. Such structure indicates that Earth’s elastic lithosphere is thicker than has been assumed in other models19–22. We also find a significant coastal gradient in relative sea level trends over this period that is unrelated to deglaciation, and suggests contributions from twentieth-century redistribution of ice and water. Our results indicate that the majority of large-scale spatial variation in longterm rates of relative sea level rise on the U.S. East Coast was due to geological processes that will persist at similar rates for centuries into the future.
  • Preprint
    Climate related sea-level variations over the past two millennia
    ( 2011-03) Kemp, Andrew C. ; Horton, Benjamin P. ; Donnelly, Jeffrey P. ; Mann, Michael E. ; Vermeer, Martin ; Rahmstorf, Stefan
    We present new sea-level reconstructions for the past 2100 years based on salt-marsh sedimentary sequences from the US Atlantic coast. The data from North Carolina reveal four phases of persistent sea-level change after correction for glacial isostatic adjustment. Sea level was stable from at least BC 100 until AD 950. It then increased for 400 years at a rate of 0.6 mm/yr, followed by a further period of stable, or slightly falling, sea level that persisted until the late 19th century. Since then, sea level has risen at an average rate of 2.1 mm/yr, representing the steepest, century-scale increase of the past two millennia. This rate was initiated between AD 1865 and 1892. Using an extended semi-empirical modeling approach, we show that these sea-level changes are consistent with global temperature for at least the past millennium.