How do we know that sea levels are rising?


Global sea level variations estimated as the common component of change across 24 globally distributed, high-resolution, continuous proxy sea level records derived from coastal sediment cores. There is a small uncertainty (±2 mm/year) in the trend over the whole record, but the shorter-term century-to-century variations are robust.

Credits: 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.

How is it measured?

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. doi:10.1073/pnas.1517056113.

Have a look on this graph:

Since at least the start of the 20th century, the average global sea level has been rising. Between 1900 and 2016, the sea level rose by 16–21 cm (6.3–8.3 in).[2] More precise data gathered from satellite radar measurements reveal an accelerating rise of 7.5 cm (3.0 in) from 1993 to 2017,[3]:1554 which is a trend of roughly 30 cm (12 in) per century. This acceleration is due mostly to human-caused global warming, which is driving thermal expansion of seawater and the melting of land-based ice sheets and glaciers.[4] Between 1993 and 2018, thermal expansion of the oceans contributed 42% to sea level rise; the melting of temperate glaciers, 21%; Greenland, 15%; and Antarctica, 8%. Climate scientists expect the rate to further accelerate during the 21st century.[5]: Source wikipedia