Paleo Constraints on Future Sea-Level Rise

Curr Clim Change Rep (2015) 1:205–215 DOI 10.1007/s40641-015-0014-6 SEA LEVEL PROJECTIONS (BP HORTON, SECTION EDITOR) Paleo Constraints on Future Sea-Level Rise Andrew C. Kemp 1 & Andrea Dutton 2 & Maureen E. Raymo 3 Published online: 17 July 2015 # Springer International Publishing AG 2015 Abstract Sea-level rise predicted for the twenty-first century and beyond will become increasingly hazardous to coastal populations, economies, static infrastructure, and ecosystems. Accurately predicting the magnitude and rate of future sealevel rise at local, regional, and global scales is necessary to effectively plan for and manage this growing hazard. Sea-level reconstructions show how high and how fast sea level rose when Earth’s climate regime was similar to that anticipated in the immediate future. We draw upon examples from the past three million years, including the Pliocene (∼3 million years ago), the Last Interglacial period (Marine Isotope Stage 5e, ∼125,000 years ago), and the Common Era (last ∼2000 years) to provide a synopsis of what is known about sea-level rise during these past warm periods and highlight some of the benefits and challenges of using paleo sealevel data to predict future changes. Keywords Pliocene . Last interglacial . Ice sheet This article is part of the Topical Collection on Sea Level Projections * Andrew C. Kemp Andrea Dutton Maureen E. Raymo 1 Department of Earth and Ocean Sciences, Tufts University, 2 North Hill Road, Medford, MA 02176, USA 2 Department of Geological Sciences, University of Florida, 241 Williamson Hall, PO Box 112120, Gainesville, FL 32611, USA 3 Lamont Doherty Earth Observatory of Columbia University, 61 Route 9 W, P.O. Box 1000, Palisades, NY 10964, USA Introduction Sea-level rise will be among the most costly and destructive consequences of climate change because it threatens coastal populations, economies, static infrastructure, and ecosystems with more frequent flooding during storms and high tides [33, 67]. This vulnerability is heightened by historic and projected increases in human activity along low-lying coastlines and, in particular, at locations which are expected to experience sealevel rise in excess of the global mean or at locations which lack the physical and/or economic resources to manage future change (e.g., [106]). Although consensus exists that climate change in the twenty-first century and beyond will cause global mean sea-level (GMSL) rise, considerable uncertainty remains as to the likely magnitude and spatial variability of those changes. Using process-based models, the Intergovernmental Panel on Climate Change (IPCC) predicted a likely increase in GMSL of 0.28–0.98 m by 2100 AD compared to the average observed between 1986 AD and 2005 AD [12]. Alternative approaches to forecasting GMSL change, some of which predict greater sea-level rise than the IPCC, include semi-empirical modeling (e.g., [79, 87]), expert elicitation (e.g., [38]), and probabilistic assessments (e.g., [44]). However, GMSL projections do not reflect the expected spatial variability of local sea-level change that will range from sea-level fall to a rise much greater than GMSL because of a range of physical processes. Developing accurate predictions of sealevel rise therefore remains a critical area of socially-relevant scientific research, particularly on the local to regional spatial scales and decadal to centennial timescales necessary for effective coastal planning and management (e.g., [68]). The need to provide appropriate analogs for current trends, and thus constraints on future changes, is a primary motivation for reconstructing paleoenvironmental changes. The geological record provides a history of coupled climate and sea- 206 Curr Clim Change Rep (2015) 1:205–215 1800 1600 CO2 (ppm) 1400 1200 RCP 8.5 RCP 6.0 RCP 4.5 RCP 2.6 Historic trend 1000 800 600 400 200 MPWP LIG A 1750 1800 1850 1900 1950 2000 2050 2100 2150 2200 Year AD Fig. 1 a Projected changes in atmospheric concentration of CO2 under four Representative Concentration Pathways (RCPs). Estimated CO2 concentrations during the mid-Pliocene warm period (MPWP) and Last Interglacial period (LIG) are displayed as a shaded horizontal band and solid line, respectively. b Modeled changes in global mean temperature benefits and challenges of using paleo sea-level data to evaluate the likely outcome of future climate change. Relative and Global Mean Sea Level RSL is the difference in elevation between the sea surface and the solid Earth at a specific location and time (e.g., [25]). RSL reconstructions are based on empirical data that estimate the height of paleo sea level. The reconstruction is produced by measuring the elevation of a paleo sea-level indicator in the field with respect to a modern tidal datum such as mean tide level. Sea-level indicators are physical, chemical, or biological proxies with a systematic and quantifiable relationship to contemporary tides (e.g., [92, 99]) and include geomorphic features (e.g., [69]), coral reefs (e.g., [24]), coral microatolls (e.g., [108]), and saltmarsh plants (e.g., [103]) or micro-organisms (e.g., [41]). Each type of indicator forms or accumulates at a particular range of elevations that is termed the indicative range and that can be established by direct measurement of modern analogs (e.g., [109]). The vertical uncertainty of a RSL reconstruction is primarily determined by the indicative range of the sea-level indicator because modern surveying techniques allow accurate and precise measurement of sample elevation. Importantly, vertical RSL errors are not systematically larger for older reconstructions, although paleo tidal range change is rarely corrected for [32, 91] and often introduces an unquantified uncertainty. To reconstruct RSL, the paleo sea-level indicator is also dated, either directly through radiometric methods (e.g., 14C or U-series), by correlation with an existing timescale such as marine oxygen isotope stages and magnetic reversals, or by correlation to other chronologies using biostratigraphy or chemostratigraphy. Temperature (°C, 1981-2010) level changes that occurred under a range of boundary conditions including varied paleogeographies, atmospheric CO2 concentrations, and orbital forcing regimes. Although future changes will be unique, the paleoenvironmental record includes time intervals characterized by warmer mean temperatures and smaller-thanpresent polar ice sheet configurations that offer insight into how local, regional, and global sea levels might respond to the climate changes predicted for the coming decades to centuries. In particular, the Representative Concentration Pathways (RCPs) are a series of socioeconomic scenarios that estimate future changes in the atmospheric concentration of greenhouse gases (e.g., [59, 65, 101]). The resulting forcing of the climate system can be used to estimate global temperature changes through climate models such as the Model for (...truncated)