Earth’s seas are rising, a direct result of a changing climate. Ocean temperatures are increasing, leading to ocean expansion. And as ice sheets and glaciers melt, they add more water. An armada of increasingly sophisticated instruments, deployed across the oceans, on polar ice and in orbit, reveals significant changes among globally interlocking factors that are driving sea levels higher. NASA works with city managers, developers and other decision-makers to help them plan for where and when waters are rising.
Seeing from Space
Only from space can we observe the height of our vast ocean on a global scale and monitor critical changes in ocean currents and heat storage. Continuous data from satellites like TOPEX/Poseidon, Jason-1, OSTM/Jason-2, Jason-3 and Sentinel-6 Michael Freilich help us understand and foresee the effects of the changing oceans on our climate and during events such as El Niño and La Niña. Visit https://sealevel.jpl.nasa.gov/ for complete information on NASA’s ocean topography missions, research and data.
Beyond the 29-year series of ocean topography missions, satellites like ICESat-2 and GRACE-FO and upcoming missions including SWOT and NISAR will also contribute to our understanding of sea level rise.
Causes of Sea Level Rise
The Role of Ice
A large fraction of the Earth’s freshwater is frozen. It is stored in glaciers all around the world and in both the Greenland and Antarctic ice sheets. When this ice melts or calves off, the water flows into the oceans and sea levels rise. Ice loss was the largest contributor to sea-level rise during the past few decades and will contribute to rising sea levels for the century to come. The ice sheets alone contributed almost 2 cm in the 15 years from 2002 and 2017.
- Greenland Ice Sheet: Three Futures
- NASA Mission Maps 16 Years of Ice Loss
- 25 Years of Antarctic Land Ice Elevation Change Anomalies
- Antarctica Exposed
The Role of a Warming Ocean
The warming of Earth is primarily due to accumulation of heat-trapping greenhouse gases, and more than 90 percent of this trapped heat is absorbed by the oceans. As this heat is absorbed, ocean temperatures rise and water expands. This thermal expansion contributes to an increase in global sea level. Temperature measurements of the sea surface, taken by ships, satellites and drifting sensors, along with subsurface measurements and observations of global sea-level rise, have shown that the warming of the upper ocean caused sea level to rise due to thermal expansion in the 20th century. Using measurements from Argo profiling floats, we know this warming has continued, causing roughly one-third of the global sea-level rise observed by satellite altimeters since 2004.
The Role of Water Storage on Land
The oceans form an integral part of the global water cycle: precipitation, evaporation and rivers move large amounts of water between land and the oceans. Since the amount of water on Earth doesn’t change, a change of the amount of water in one component must be offset against the other. Because the water cycle varies over time, the amount of water stored in the ocean varies over time as well. For example, heavy rains over Australia, Southeast Asia, and the Amazon Basin -- and the subsequent storage of large amounts of water on land -- caused a temporary drop in global sea level of 1 cm during the 2010-2011 La Niña cycle.
Humans also directly change the amount of water on land, and thus the amount of water in the oceans. The global construction of large dams on rivers has led to the impoundment of an amount of water equal to 3 cm of sea level. On the other hand, in many places, groundwater from non-recharging aquifers is consumed by human civilization, and this water eventually ends up in the oceans, adding to global sea-level rise.
The Role of Rebound and Subsidence
It’s not only water processes that play a role in global sea level rise – ground movements can play a significant role as well in regional vulnerability. On a continental scale, Earth’s crust is still recovering from the last ice age. Around 20,000 years ago, Canada, the northeast United States, Scandinavia and other regions were weighed down by ice sheets. As these ice sheets melted and the weight on the continents eased, the land surface slowly rebounded. This rebounding process, and related subsidence, continues to alter the shape of ocean basins today. Subsidence can also result from human activity, like resource extraction.
Effects of Sea Level Rise
High Tide Flooding
Sea level rise is often spoken of in future terms, including projections for impacts we’re likely to see by the end of the century. But in many communities in the U.S., sea level rise is already a factor in people’s lives in the form of high-tide flooding.
High-tide floods, also known as nuisance floods, sunny-day floods and recurrent tidal floods, occur “when tides reach anywhere from 1.75 to 2 feet above the daily average high tide and start spilling onto streets or bubbling up from storm drains,” according to an annual report on the subject by the National Oceanic and Atmospheric Administration (NOAA.) These floods are usually not related to storms; they typically occur during high tides, and they impact people’s lives. Because of rising seas driven by climate change, the frequency of this kind of flood has dramatically increased in recent years.
Regional Sea Level Rise
In the northeastern Pacific off the U.S. West Coast, sea level rise was 4 to 5 mm a year lower than the global average during the 1990s and 2000s. Then around 2010, sea level began steadily increasing along the West Coast. The largest increase, in 2014-16, coincided with a large El Niño event in 2015-16. While the rate has stabilized since then, it remains higher than the global average.
Infrastructure at Risk
Sea level rise has not stopped people from buying and building along the coast. About 55 to 60 percent of U.S. citizens live in counties touching the Atlantic or Pacific Ocean, the Gulf of Mexico, or the Great Lakes. A recent study by business and finance leaders found that $66 billion to $106 billion worth of coastal property is likely to sit below sea level by 2050.
The nation’s problem is also NASA’s problem, and not just because several satellites and hundreds of Earth scientists are monitoring the rising seas. Sea level rise hits especially close to home because half to two-thirds of NASA’s infrastructure and assets stand within 16 feet (5 meters) of sea level.
NASA’s Sea Level Change Portal
Experience NASA’s Sea Level Change portal for an in-depth look at the science behind global and regional sea level, plus news, data, and features.
Infographic: Explore the science and future of global sea level rise
A collection of resources to enable educators to share information about sea level missions, the STEM-related careers of several scientists and engineers, as well as the science behind the recent Sentinel-6 Michael Freilich mission. These resources have been aligned to Next Generation Science Standards (NGSS) to assist with curriculum planning.
As human activity warms our planet, the ocean absorbs over 90 percent of the excess heat. This increases water volume and melts ice sheets and glaciers, contributing to sea level rise. Watch the video to learn how much global sea level is rising each year, what that looks like in everyday terms, and why it matters.
Over 90 percent of Earth’s ice mass is locked up in Greenland and Antarctica. As our greenhouse gas emissions warm the planet, those areas, along with glaciers worldwide, lose more ice, contributing to sea level rise. Watch the video to learn how many people are threatened by this phenomenon worldwide and how much global sea level is projected to rise by 2100.
Land Ice vs. Sea Ice
Time lapse video simulating sea ice and land ice melting in an aquarium and its effect on sea level rise.
- NASA’s Earth Minute on Sea Level Rise
- What Determines the Level of the Sea?
- Earth Science Basics: Sea Level Rise
What's Causing Sea-Level Rise? Land Ice Vs. Sea Ice
A classroom activity demonstrating to students how melting ice contributes to sea-level rise.
How thick is Greenland’s Ice?
A color by number Data Viz activity featured in Earth Observatory for Kids