Water covers 71% of the Earth’s surface, and sea levels depend largely on the water’s temperature and how much is stored in the form of ice. As temperatures continue to rise due to human greenhouse gas emissions, glacier melt and sea level rise are accelerating.
Past sea levels can be reconstructed from the dominant patterns found in seven proxies, based on marine δ18O records, magnesium to calcium ratios, coral benchmarks, hydraulic modeling of evaporation mechanisms and ice sheet records. This geologic reconstruction covers the time period from around 800,000 to 3,000 years ago.
The next time window spans from 3,000 years ago to 1890. Scientists based their reconstruction on a combination of geologic records and tide gauge data. They looked at the changes across 24 globally distributed locations, from which sediment cores were obtained. These provide high-resolution data with little uncertainty, hence the change in the curve’s character.
Between 1890 and 1993, sea levels were measured mainly using tide gauges. After 1980, satellite altimetry data was also available, providing a second dataset to corroborate the tide gauge information.
For the past 30 years or so, sea levels have been precisely measured thanks to satellites. Comparison with tide gauge data helped smooth out historic reconstructions and a clear acceleration in sea level rise rates was observed.
References
Spratt, R.M. and L.E. Lisiecki. 2016. A late Pleistocene sea level stack. Climate of the Past, Vol. 12, pp. 1079-1092. doi:10.5194/cp-12-1079-2016.
Kopp, R.E., A.C. Kemp, K. Bittermann, B.P. Horton, J.P. Donnelly, W.R. Gehreis, C.C. Hay, J.X. Mitrovica, E.D. Morrow, and S. Rahmstorf. 2016. Temperature-driven global sea-level variability in the Common Era. Proceedings of the National Academy of Sciences, Vol. 113, pp. E1434-E1441. doi:10.1073/pnas.1517056113.
Church, J.A. and N.J. White. 2011. Sea-level rise from the late 19th to the early 21st Century. Surveys in Geophysics, doi:10.1007/s10712-011-9119-1.
Nerem, R. S., D. Chambers, C. Choe, and G. T. Mitchum.
The 2 degree Institute: https://www.sealevels.org/
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