This is part of a series on the effects of climate change.
What is causing sea level to rise?
There are two main causes of sea level rise: warming ocean temperatures and melting land ice. When water heats up, it expands. Oceans are estimated to have absorbed around 90 percent of the excessive heat trapped on Earth’s surface. In 2023, the global ocean surface temperature was around 0.9 degrees Celsius warmer than the 20th-century average. In turn, steric sea surface height – the volume associated with changes in temperature and salinity - increased by 23.5 millimeters between 2005 and 2023. Thermal expansion is estimated to have accounted for roughly one-third of annual sea level variation worldwide this century.Meanwhile, it is estimated that increasing ocean mass has added an annual average of two millimeters to sea level rise in the past two decades. As of January 2024, the ocean mass increase worldwide was around 34.4 millimeters compared with 2002 levels. Ocean mass variation stems from the melting of glaciers and Greenland and Antarctic ice sheets. Existing land ice masses hold enough water to increase sea level by 65 meters, although it is forecast that under a very high greenhouse gas emissions scenario, the contribution of land ice to sea level rise would be around 30 centimeters by 2100.