China

Sea level rise refers to the increase in the height of the ocean’s surface, which affects coastlines around the world. Measuring this change is crucial for understanding the rate and effects of rising seas on both global and local scales. Scientists use two main tools to track sea level changes: tide gauges and satellites. Tide gauges, which provide us with data going back more than a century in some places, measure local or relative sea level by tracking water levels compared to the adjacent land. Over the last three decades, satellites equipped with radar altimeters started providing precise ocean heights from space across the globe. Tide gauges and satellites (altimetry data) together give us a comprehensive view of how sea levels are changing over time, offering insight into both regional and worldwide patterns.  

Climate change is the primary driver of contemporary sea level rise. Global warming due to anthropogenic emissions is contributing to sea level rise in two primary ways. First, higher temperatures cause the ocean water itself to expand - a process called thermal expansion. Approximately 90 percent of this additional heat is being absorbed by the oceans. Second, warming accelerates the melting of glaciers and polar ice sheets, adding large amounts of water to the oceans. Combined, these processes are pushing sea levels higher, making coastal flooding more frequent and intensifying the risks for communities and infrastructure near coasts. Rising sea levels not only creates stress on the physical coastline, but also on coastal ecosystems. For example, saltwater intrusions can contaminate freshwater aquifers, many of which sustain municipal and agricultural water supplies and natural ecosystems. As global temperatures continue to warm, sea level will keep rising long into the future due to the substantial lag to reaching an equilibrium.

Recent studies indicate that the pace of global sea level rise has doubled since the early 1990s (Hamlington et al., 2024), underscoring the extreme risk of coastal inundation due to sea level rise over the coming decades.   

Global and Regional Sea Level Change. While the overall rise in global sea level provides a broad measure, local sea level change can vary greatly due to regional factors. These factors include ocean currents, water temperature and salinity, vertical land movement (where land itself may rise or sink), and regional weather phenomena such as tropical cyclones or the El Niño-Southern Oscillation (ENSO). For example, the U.S. Gulf Coast is experiencing faster-than-average sea level rise due to a combination of sinking land and warmer ocean currents, while parts of Alaska have relatively stable or even decreasing sea levels (as measured by tide gauges) because the land is rising. This variability highlights that while global sea level rise is a universal trend, the effects and risks differ widely by region, posing unique challenges for each coastal community.  

This page explores the historical changes in sea levels, providing insights into how the past informs our understanding of present and future trends. Data can be explored by either Tide Gauge or spatial aggregation for Exclusive Economic Zones.​

CCKP is grateful for the support and expertise of NASA's Sea Level Change Team (N-SLCT). All data presented has been provided by N-SLCT. For additional details about the science behind sea level change, users are encouraged to visit: https://earth.gov/sealevel 

01 - Global Sea Level Change (1993-Present)​

Historical sea level rise has been significant, with global mean sea level increasing by approximately 210–240 millimeters since 1880. Over one-third of this rise has occurred in just the past 25 years, highlighting an accelerating trend. This rise is largely attributed to the thermal expansion of warming ocean waters and the melting of land-based ice, including glaciers and polar ice sheets. Tide gauges have captured localized changes, while altimetry data since the 1990s have provided precise global measurements. Together, these records reveal a clear upward trajectory in sea levels.​

What you can see in this figure
The chart shows the global sea level change that has taken place over the last three decades, from 1993 to now, measured by satellite altimetry and adjusted for nearby land movement. It highlights seasonal cycles and yearly fluctuations, as well as the long-term upward trend, despite intra-annual and inter-annual variability.

Satellite altimetry data has been collected since 1993. Time series are updated monthly. Satellite altimetry and reconstruction data found within the boundaries of the Exclusive Economic Zone are averaged together to form time series. 

Understanding the Data: Implications and Utility
Sea level exhibits a clear seasonality, primarily driven by the annual warming and cooling cycles of the oceans and changes in land-water storage, alongside notable interannual variability influenced by phenomena like ENSO, and a long-term trend resulting from global warming and ice melt. Sea level rise is particularly dangerous for low-lying coastal areas and small island nations, as it exacerbates and compounds risks from other hazards, including cyclones, storm surges, and salinization.

 

02 - Historical Sea Level Change​ By Exclusive Economic Zone, Tide Gauge

Below, we illustrate the regional variations in sea level rise.

​What you can see in this figure
The map shows the sea level change that has taken place over the last three decades, from 1993 – 2024. Data is presented by Exclusive Economic Zone or tide gauge. Clicking on a tide gauge 'cluster' will zoom-in to allow for selection of an individual tide gauge. 

Understanding the Data: Implications and Utility
In the map, users can readily discern regional differences and access data from various areas, providing a comprehensive picture of where sea level rise is most prominent.

What you can see in this figure
The chart shows the regional sea level change that has taken place over the last three decades, from 1993 to now, measured by satellite altimetry and adjusted for nearby land movement. It highlights seasonal cycles and yearly fluctuations, as well as the long-term upward trend, despite intra-annual and inter-annual variability. It can be visualized as a seasonal cycle for each year (12 months) or as a complete time series from 1993 to now.

Satellite altimetry data has been collected since 1993. Time series are updated monthly. Satellite altimetry and reconstruction data found within the boundaries of the Exclusive Economic Zone are averaged together to form time series. 

Understanding the Data: Implications and Utility
Sea level exhibits regional differences. It also exhibits a clear seasonality, primarily driven by the annual warming and cooling cycles of the oceans and changes in land-water storage, alongside notable interannual variability influenced by phenomena like ENSO, and a long-term trend resulting from global warming and ice melt. Sea level rise is particularly dangerous for low-lying coastal areas and small island nations, as it exacerbates and compounds risks from other hazards, including cyclones, storm surges, and salinization.

03 - Contributors to Sea Level Rise

This section explores the main drivers of sea level rise, including key processes such as the melting of ice sheets and glaciers, vertical land motion, and sterodynamics. Together, these processes shape the patterns of regional and global sea level change, influencing coastal communities and ecosystems.​​

What you can see in this figure
This pie chart highlights the contributions of different factors to sea level change in a selected location from 1993 to 2024. 

Understanding the Data: Implications and Utility
Notice how different areas are affected differently by the various processes. The primary contributions to global sea level rise thus far are:

  • Thermal expansion of ocean water: As oceans absorb the vast majority of excess heat trapped by greenhouse gases, the water expands in volume.
  • Melting of land-based ice: This includes the accelerated melting of glaciers, mountain ice caps, and the massive Greenland and Antarctic ice sheets, adding substantial amounts of water to the oceans.

A smaller, yet still contributing, factor is the changes in land-water storage, such as groundwater depletion.

The percent contributions are expected to change into the future.

  1. Ice Sheets and Glaciers: The melting of the Greenland and Antarctic Ice Sheets, along with the widespread retreat of mountain glaciers, significantly contributes to sea level rise by releasing freshwater into the oceans. Warmer global temperatures accelerate this process, further melting ice and glaciers and adding more water to the sea.​

  2. Vertical Land Motion: Local sea levels are influenced by whether the land is rising or sinking. Vertical land motion, caused by natural processes like tectonic shifts or human activities such as groundwater extraction, can either elevate or lower local sea levels, creating regional variations in the overall trend.​

  3. Sterodynamics: This term refers to the combined effects of ocean warming and changes in ocean currents, both of which are influenced by climate change. As the ocean absorbs more heat, water expands (thermal expansion), and shifting ocean currents, driven by added freshwater from melting ice and altered heat transport, impact regional sea levels, causing further variability.​

  4. Terrestrial (land) Water Storage: Changes in terrestrial water storage, such as groundwater depletion or the accumulation of water in reservoirs and soils, can influence local sea levels. Pumping groundwater adds water to the ocean, raising sea levels, while water retained on land can temporarily lower them.

04 - High Tide Flooding

High Tide Flooding (HTF) refers to events where sea levels exceed a specific threshold above the average high tide, and can potentially lead to flooding. Three defined thresholds - minor: 40cm (400mm), moderate: 60cm (600mm), and major: 80cm (800mm) - mark increasing levels of high water that may indicate worsening flooding risks.

What you can see in this figure
This line chart displays the annual number of days in a selected location when sea levels exceeded three thresholds for high tide flooding: minor (40 cm), moderate (60 cm), and major (80 cm) above the average high tide. The chart provides a time series that highlights how the frequency of exceedances has changed over the years, indicating the potential for increased flooding severity as sea levels rise.

Understanding the Data: Implications and Utility
In most cases, high tide flooding is becoming more frequent due to rising sea levels.