Sea level rise is likely to be one of the most serious and tangible consequences of future climate change. It is, as a consequence, a critical research challenge. Confidence in future projections will be dictated by our ability to correctly account for observed sea level changes from the recent past.
Variations in sea level are determined by three main components: (i) changes in the density of the oceans which is primarily influenced by temperature; (ii) changes in the mass of the oceans which is influenced by glaciers, ice sheets and land hydrology; and (iii) changes in the shape of the ocean floor and land surface due to long-term adjustments in the Earth’s crust. Significant uncertainties exist in each of these components and their sum falls significantly short of the observed sea level record from tide gauges most of over the twentieth century  – sometimes described as the “sea level enigma”.
Read more about the challenge:
 Hay, C. C., E. Morrow, R. E. Kopp and J. X. Mitrovica (2015). “Probabilistic reanalysis of twentieth-century sea-level rise.” Nature.