Past sea level has varied by somewhat more than a hundred metres. This is primarily due to the growth and decay of ice sheets (mostly in the northern hemisphere) with water evaporated from the sea. The Mediterranean Basin's gradual growth as the Neotethys basin, begun in the Jurassic, did not suddenly affect ocean levels. While the Mediterranean was forming during the past 100 million years, the average ocean level was generally 200 metres above current levels. However, the largest known example of marine flooding was when the Atlantic breached the Strait of Gibraltar at the end of the Messinian Salinity Crisis about 5.2
Sea level rise challenging, due to our imperfect understanding of many aspects of the climate system. As climate research leads to improved computer models, projections have consistently increased. For example, in 2007 the Intergovernmental Panel on Climate Change (IPCC) projected a maximal rise of through 2099, but their 2014 report raised the high-end estimate to about . A number of later studies have concluded that a global sea level rise of this century is "physically plausible". The contributing factors to sea level rise between 1993 and 2018 are thermal expansion of the oceans (42%), melting of temperate glaciers (21%), Greenland (15%) and Antarctica