Climate Rising seas mainly due to expansion of warmer water
Warmer seawater is causing sea levels to rise significantly, a new study shows. In the period from 1960 to 2023, this warming-induced expansion was responsible for 43 percent of the rise, as calculated by a research team in Beijing.
24.05.2026, 05:27
SDA
The water from melting mountain glaciers contributed 27 percent to the rising water levels, the melting ice masses in Greenland 15 percent and in the Antarctic 12 percent. The research team led by Lijing Cheng from the Chinese Academy of Sciences in Beijing published their results in the journal "Science Advances".
On average, the sea level rose by 2.06 millimetres per year over the more than 60-year period. In the years 2005 to 2023, the average was even 3.94 millimetres per year.
There are two main causes of sea level rise as a result of climate change: Firstly, more water is entering the world's oceans due to the melting of glaciers and ice sheets in the polar regions. Secondly, the seawater absorbs around 90 percent of the heat that is held in the atmosphere - the oceans are therefore a huge buffer against the rise in air temperatures caused by global warming. Because heat is generated by a stronger movement of particles, warmer water requires more space than colder water: the seawater therefore expands.
Understanding the causes of the rise is essential for forecasts
"Understanding the causes of sea level rise is essential for forecasting future sea level changes and supports climate adaptation and mitigation efforts," write the study authors. Cheng and colleagues made use of new observation methods, particularly satellites, as well as improved analyses that correct for systematic errors in the measurement methods.
They divided their analysis into several time periods: For example, the long-term observation (1960 to 2023) is composed of the improved analysis of tide gauges (1960 to 1992) and satellite altimetry (1993 to 2023). From 2005, the researchers also used data from the drifting buoys of the mobile observation system for the world's oceans, Argo.
Seawater melts ice shelves from below
The individual contributions in the most recent period are somewhat different from those in the long-term observation: for example, the increasingly rare mountain glaciers recently contributed 19.3 percent less to the rise, compared to 27 percent in the long term. In contrast, the ice sheets in Greenland and Antarctica are now contributing slightly more.
Only recently, a study in the scientific journal "Nature Communications" explained how the warming of the oceans is accelerating the melting of Antarctic ice. The team led by Tore Hattermann from Tromsø, Norway, described channels on the underside of the ice shelf in which relatively warm water collects and melts the ice from below. As the ice shelf melts, the supporting effect for the land ice sometimes disappears, which is why it moves faster towards the sea. According to current knowledge, however, it is likely to take centuries for the polar ice sheets to melt completely.
Study on subsidence in coastal cities
In a recent study, also published in "Nature Communications", researchers from the Technical University of Munich (TUM) draw attention to another danger for coastal cities: subsidence. They are mainly caused by excessive extraction of water and raw materials that previously stabilized the subsoil. The heavy weight of cities and long-term geological processes can also promote subsidence.
"In many large coastal cities, groundwater abstraction is a major driver of land subsidence," senior author Florian Seitz is quoted as saying in a TUM press release. "This means that local political and water management decisions can make a big difference."
