What is global mean sea level?
This is the average height of the entire ocean surface. Global mean sea level rise is caused primarily by two factors related to global warming: the added water from melting land-based ice sheets and glaciers and the expansion of seawater as it warms.
What are we looking at?
The plot shows global change in sea level since 1993, as observed by satellite altimeters. The black line tracks the measurements, while the blue line shows how much uncertainty is associated with these measurements. Based on data from 2024.
Why do we care?
Global mean sea level is an important climate indicator, providing information on how the ocean is warming and how much land ice is melting. Global sea levels have been rising for decades in response to a warming climate. The annual rate of rise – or how quickly sea level rise is happening – has also increased from 0.08 inches/year (0.20 centimeters/year) in 1993 to the current yearly rate of 0.17 inches/year (0.44 centimeters/year). Data on this increase in the rate of global sea level rise is critical to planners understanding the trajectory of future sea level rise. More information on the importance of the 30-year satellite record and data on the trajectory of global mean sea level can be found here. References: Willis, Hamlington, Fournier, 2023. Beckley et al., 2017; GMSL dataset.
Sea level rise projections
Sciences on global mean sea level (GMSL), sea level rise (SLR), an overview of current, past, and future sea level.
Global and European sea level rise
Global mean sea level has risen about 21cm since 1900, at an accelerating rate. GMSL reached its highest value ever in 2023. GMSL will likely rise by 0.28-0.55m under a very low emissions scenario (SSP1-1.9) and 0.63-1.02m under a very high emissions scenario (SSP5-8.5) by 2100, relative to the 1995-2014 average. GMSL simulations that include the possibility of fast disintegration of the polar ice sheets project a rise of up to 5m by 2150. Most coastal regions in Europe have experienced an increase in sea level relative to land, except for the northern Baltic Sea coast.
Observed and projected change in global mean sea level
Left Chart
The left chart depicts the rise in global mean sea level from 1900 to 2023 based on two data sources. All values are relative to the average level of the period 1993-2010, during which the two datasets overlap.
The green line (Palmer et al., 2021) shows the ensemble sea-level reconstruction (using five members) of sea level anomalies during 1900-2010 (Palmer et al., 2021; https://iopscience.iop.org/article/10.1088/1748-9326/abdaec#erlabdaecs2).
The orange line (CMEMS) shows the filtered sea level anomalies corrected for the TOPEX-A instrumental drift (Ablain et al., 2017; WCRP Sea Level Budget Group, 2018), corrected for the GIA using the ICE5G-VM2 GIA model (Peltier, 2004), for the time series from 1993 to 2023.
The right chart shows global mean sea level projections under different SSP scenarios. Sea level projections considering only processes for which projections can be made with at least medium confidence are provided, relative to the period 1995–2014, for five Shared Socioeconomic Pathway (SSP) scenarios. The scenarios are described in sections TS1.3 and 1.6 and Cross-Chapter Box 1.4 of the Working Group 1 contribution.Sea level projections considering only processes for which projections can be made with at least medium confidence are provided, relative to the period 1995–2014, for five Shared Socioeconomic Pathway (SSP) scenarios. The scenarios are described in sections TS1.3 and 1.6 and Cross-Chapter Box 1.4 of the Working Group 1 contribution.
Right Chart
The right chart shows global mean sea level projections under different SSP scenarios. Sea level projections considering only processes for which projections can be made with at least medium confidence are provided, relative to the period 1995–2014, for five Shared Socioeconomic Pathway (SSP) scenarios. The scenarios are described in sections TS1.3 and 1.6 and Cross-Chapter Box 1.4 of the Working Group 1 contribution.Sea level projections considering only processes for which projections can be made with at least medium confidence are provided, relative to the period 1995–2014, for five Shared Socioeconomic Pathway (SSP) scenarios. The scenarios are described in sections TS1.3 and 1.6 and Cross-Chapter Box 1.4 of the Working Group 1 contribution.
General description
The global mean sea level (GMSL) in 2023 was the highest ever measured by the satellite-based monitoring system. GMSL reconstructions based on tide gauge observations show a rise of 21cm from 1900 to 2020 at an average rate of 1.7mm/year. The rate of GMSL rise accelerated to 3.3mm/year over the period 1993-2018 and 3.7mm/year over the period 2006-2018, more than twice as fast as during the 20th century.
Since 1970, anthropogenic forcing has been the predominant cause of this accelerating sea level rise both globally and in European regional seas. Thermal expansion of ocean water was initially the main driver, however melting of glaciers and of the Antarctic and Greenland ice sheets have exceeded the effects of thermal expansion since about 2000.
Global climate models project that the rise in GMSL during the 21st century (i.e. by 2100, relative to the period 1995-2014), with 66% confidence, will likely be in the range of 0.28-0.55m for a very low emissions scenario (SSP1-1.9). For an intermediate emissions scenario, 0.44-0.76m (SSP2-4.5) and 0.63-1.02m for a very high emissions scenario (SSP5-8.5). Model simulations that include the possibility of fast disintegration of the polar ice sheets, which is assessed to have a low likelihood, project a GMSL rise of up to about 5m by 2150 under a very high emissions scenario (SSP5-8.5).
The future behaviour of the Greenland and Antarctic ice sheets is still rather uncertain, particularly under higher emissions scenarios. Studies considering processes that can lead to a faster disintegration of the Antarctic ice sheet, including a potential collapse of marine-based sectors, have estimated a GMSL rise of up to 2.3m by 2100 and up to 5.4m by 2150. The consideration of such high-end scenarios is important for long-term coastal risk management, in particular in densely populated coastal zones. Each five year delay in the peaking of global greenhouse gas emissions increases the median sea-level rise projections for 2300 by 0.2m and extreme sea-level rise projections (95th percentile) by up to 1m.
The NASA Sea Level Projection Tool allows users to visualise and download the sea level projection data from the Intergovernmental Panel on Climate Change (IPCC) 6th Assessment Report (AR6).
Past trend and projected change in relative sea level across Europe
Most European coastal regions experience increases in both absolute sea level (as measured by satellites) and relative sea level (as measured by tide gauges), the latter being more relevant for coastal protection. There are sizeable differences in the rates of sea level change across Europe. Notably, sea levels relative to land along the northern Baltic Sea coast and — to a lesser degree — the northern Norwegian coast are sinking. This is due to rising land levels caused by post-glacial rebound since the last ice age.
In future, relative sea level change along most of the European coastline is projected to be reasonably similar to the global average. Main exceptions are the northern Baltic Sea and the northern Norwegian coasts, which are experiencing considerable land rise as a consequence of post-glacial rebound and changes in the gravity field of the Greenland ice sheet. As a result, sea level relative to land in these regions will continue to rise more slowly than elsewhere or may even decrease. Further information on past and projected changes sea level rise in Europe is available on the European Climate Data Explorer. A dedicated EU policy sector page on coastal areas is available on Climate-ADAPT.
European Environment Agency – The EEA is an agency of the European Union. Together with the Eionet network, we provide the knowledge and the data needed to achieve sustainability in Europe.
This indicator comprises several metrics to describe past and future sea level rise globally and along European coastlines:
- Observed change in global mean sea level, based on reconstructions from tide gauge measurements (since 1900) and on satellite altimeter data (since 1993);
- Projected change in global sea level for five different forcing scenarios and spatial trends in relative sea level along the European coastline, based on tide gauge stations with long time series (since 1970).
Methodology for indicator calculation
Sea level changes can be measured using tide gauges and remotely from space using satellite altimeters. Many tide gauge measurements have long multi-decadal time series, with some exceeding 100 years. However, the data can be distorted by various regional and local effects, such as vertical land motion processes. Furthermore, there are significant gaps in the spatial coverage of tide gauges with long time series, including in Europe.
Satellite altimeters enable absolute sea level to be measured from space and provide much better spatial coverage (except at high latitudes); however, their record is limited to about 30 years. The global and European sea level trends are calculated from a combination of nine partly overlapping satellite missions. The data are corrected for seasonal variations, the inverse barometer effects and post-glacial rebound.
Sea level projections are based on process-based models, which are rooted in state-of-the-art climate model simulations. Projections for relative mean sea level in Europe consider the gravitational and solid Earth response and land movement due to glacial isostatic adjustment, but not land subsidence as a result of human activities.
Model-based projections for changes in regional sea level rise included only grid cells that are covered at least half by sea. Data for other grid cells partly covered by land and by sea were extrapolated using the nearest-neighbour method.
Policy/environmental relevance
Justification for indicator selection
No rationale for indicator selection have been specified.
Context description
Sea level is an important indicator of climate change because it can have significant impacts on settlements, infrastructure, people and natural systems. The potential impacts include flooding, coastal erosion and the submergence of flat regions along continental coastlines and on islands. Rising sea levels can also cause saltwater intrusion into low-lying aquifers, thus threatening water supplies and endangering coastal ecosystems and wetlands.
Changes in global mean sea level result from a combination of several physical processes. Thermal expansion of the oceans occurs as a result of warming ocean water. Additional water is added to the ocean from a net melting of glaciers and small ice caps, and from the disintegration of the large Greenland and Antarctic ice sheets.
The locally experienced changes in sea level differ from global average changes for various reasons, including changes in large-scale ocean circulation, changes in the gravity field, and vertical land movement due to the ongoing effects of post-glacial rebound, local groundwater extraction or other processes.
Accuracy and uncertainties
No uncertainties have been specified.
For references visit the linked content source.
Visit ClimateCentral for various maps related to sea level rise.
U.S. Sea Level Change
Key Takeaways
- Sea level will continue to rise globally well into the future as long as the planet continues warming from greenhouse gas emissions.
- For the United States, sea level rise will likely reach around 12 inches (1 foot) by 2050. By 2100, it will likely reach between 2.3 feet and 4 feet, but higher amounts are possible and and depend on greenhouse gas emissions.
- Sea level rise will be higher or lower in some places due to local factors, like changes in land height and ocean currents.
- Sea level will still rise for centuries after greenhouse gas emissions stop.
For more visit sealevel.globalchange.gov
Projections Accounting for more Processes
The following sea level projections are based on past rapid sea level rise and taking into account physical processes of ice-sheet disintegration. IPCC projections are considered more conservative, since the reports not always reflect the latest research and are selective.
Barclay Kamb 1990
In this talk titled, ‘Is the Antarctic Ice Sheet Disintegrating?’ Kamb looks at the possibilities of West Antarctic ice sheet disintegration, he mentions the possibility of multi-meter sea level rise in the order of decades.
Blanchon et al. 2009
Blanchon and three colleagues from the Leibniz Institute of Marine Science in Germany discovered the remains of coral reefs that made it possible to measure with great precision changes in sea level. Using contiguous reef crests — the part of the reef closest to the surface of the water — as benchmarks, the researchers pinpointed a dramatic jump in sea levels that occurred 121,000 years ago.
“We are looking at a three-metre rise in 50 years,” Banchon said.
“This is the first evidence that we have for rapid change in sea level during that time.” Only collapsing ice sheets could account for such an abrupt increase, he added. The last interglacial period, when sea levels peaked six metres higher than current levels, was warmer than the world is today.
Hansen et al. 2025
According to Hansen et al. 2025, based on novel climate simulations which consider nonlinear ice sheet dynamics, with the worst case scenario of multi-meter sea-level rise in the next 50 to 150 years.
The West Antarctic ice sheet is vulnerable to collapse because it is a marine ice sheet sitting on bedrock hundreds of meters below sea level. There is evidence that it collapsed during the Eemian period – the last interglacial period that was warmer than the interglacial period that we live in – and now, with the rapid warming of the past 50 years, Earth is as warm as it was during the Eemian. The process of ice sheet collapse is believed to be initiated by a warming ocean melting the ice shelves that extend from the ice sheet into the ocean, providing a buttress for the ice sheet. Those ice shelves are now melting because the ocean is warming. We do not know how far the ice shelf melting must reach before ice sheet collapse becomes inevitable.
Our climate simulations led to the staggering conclusion that continued growth of ice melt will cause shutdown of the North Atlantic and Southern Ocean overturning circulations as early as midcentury and “nonlinearly growing sea level rise, reaching several meters in 50-150 years. The 50-150 year range reflects the 10-20 year estimate for doubling time of freshwater injection into the ocean.
Eric Rignot 2021
Eric Rignot: “At the current rates of progression since the 1990s, we are heading for 1 m sea level rise (SLR) by the end of the century, but there is a distinct possibility it could go faster, especially if parts of Greenland or Antarctica fall apart rapidly, aka 10 times faster than present is possible, we just do not know. In which case, we will be facing a foot per decade rather than a few feet per century.
We have to take these changes very seriously. The alarm bell has been ringing, so loud we cannot ignore it. While the science keeps working at reducing uncertainties of future rapid sea level change, we have to pull our sleeves up, and work very hard to transition to zero carbon energy production, and curb the concentration of greenhouse gases in the atmosphere using that and also carbon sequestration.
Both will be needed to avoid disastrous situations in the future. And we do not want to go there to prove science to be right. Science is about telling us “Do not go there”. And as a scientist, I am saying “Do not go there, we know enough to tell you that multiple meters of sea level rise in the coming century could be a reality if we do nothing”. If we work hard, however, there is still time.”
The data presented on global mean sea level rise is alarming, particularly in light of the accelerated rates observed since the 1990s. Understanding these projections is crucial for effective climate policy and coastal planning.
Indeed, the implications of rising sea levels extend beyond environmental concerns; they challenge socio-economic structures and necessitate adaptive strategies in urban planning.
Absolutely, the urgency for immediate action cannot be overstated. The scientific consensus underscores the critical need for mitigating greenhouse gas emissions to prevent catastrophic outcomes.