Sea surface height increases not only as water is added, but also as water warms and its volume expands. Changes in salt content, or salinity, also affect sea levels. These are known as “thermosteric” and “halosteric” changes.
A global system of floating ocean sensors, known as “Argo,” measures ocean temperature and salinity from the surface to a depth of about 6,600 feet (2,000 meters). Argo floats tell us how much of known sea level rise can be attributed to increased temperature as sea water expands.
Warming and expanding ocean water contributes about one-third of known sea level rise over decades, as the ocean absorbs 90% of the heat trapped in Earth’s atmosphere. Combined with measurements of land ice melt that adds water to the ocean, we can identify and measure the processes contribution to global mean sea level rise.