Bruna Alves
Research lead covering environment and sustainability
Sea level rise - statistics & facts
Sea level is defined as the average level of the sea relative to the adjacent land, and it can vary according to climatic conditions. The global sea level has increased by around 90 millimeters since 1993, at an average of 2.9 millimeters per year. This increase was not constant, with the rate accelerating in the past decade. Depending on the development of emissions, projected changes in sea level worldwide indicate a rise of between 38 and 77 centimeters by 2100, affecting coastal areas and marine ecosystems around the world.
This is part of a series on the effects of climate change.
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.
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.
The effects of sea level rise
A rise in sea level represents a threat to coastal areas across the globe. Risks include an escalation in coastal erosion, more frequent and intense storm surges and flooding, and damage to wildlife habitats such as marshes and wetlands. The annual flooded area of small island states due to sea level rise is expected to reach 30 square kilometers by 2100, a sixfold increase compared to the figure from 2020. Moreover, in the U.S., Florida will be the most affected state by sea level rise, with around 21 percent of its housing units projected to be in high risk flooding zones by the end of the century. However, the threats of sea level rise are not limited to life on land. There are disturbances to the circulation of ocean currents that help regulate local climates and disruptions to marine ecosystems that are sensitive to the changes in temperature and salinity associated with climate change.
