Worried about what sea level rise means for coastlines you care about? Global seas have risen 8-9 inches since 1880, driven mostly by melting ice and warming water, and the rate is speeding up.
Rising seas are one thread in the wider story of climate change, and this page explains how that thread works.
| Item | Value |
|---|---|
| Global average rise since 1880 | 8-9 inches (21-24 centimeters) |
| Average rate through most of the twentieth century | 1.4 millimeters per year |
| Average rate, 2006-2015 | 3.6 millimeters per year |
| Rate from 1993 to 2020 (NASA) | About 3.3 millimeters per year |
| Global average in 2023 versus 1993 levels | 101.4 mm (3.99 inches) higher |
| Projected U.S. rise by 2100 with significant emission cuts | Around 0.6 meters (2 feet) above 2000 |
The figures come from NOAA Climate.gov and NASA Science. Measurements and projections can change, so check the source before you rely on them.
What is driving sea level rise?
The short answer is heat. NASA’s sea level portal puts the observed rise at about 3 mm per year, with about 2 mm per year from meltwater off land-based ice sheets and mountain glaciers and roughly 1 mm per year from thermal expansion, according to NASA Sea Level Change.
Three processes explain the rise:
- Melting land ice: glaciers and ice sheets add water to the ocean. NASA Science says they add hundreds of gigatons of meltwater each year.
- Thermal expansion: ocean water takes up space as it warms, which lifts the surface even with no extra water.
- Changes in land water: water stored behind dams, pumped from aquifers or shifted by rainfall patterns makes a small contribution.
NOAA describes the land-water share as much smaller than the other two, and says it is largely due to people depleting groundwater, per NOAA Climate.gov. Ocean waters are expanding because they absorb massive amounts of heat trapped by greenhouse gases, as NASA Science explains.
How much have seas risen so far?
NOAA reports that global average sea level has risen 8-9 inches (21-24 centimeters) since 1880. In 2023, the global average hit a record 101.4 mm (3.99 inches) above 1993 levels, the highest annual value in the satellite record that starts in 1993, according to NOAA Climate.gov.
That page was published on August 22, 2023, and it carries a notice that it was archived as of June 25, 2025 and is no longer updated. Newer annual figures may therefore differ from those quoted here.
The pace matters as much as the total. The rate more than doubled, from 1.4 millimeters per year through most of the twentieth century to 3.6 millimeters per year from 2006-2015, which NOAA calls 2.5 times the earlier rate.
NASA’s own satellite record tells a similar story. NASA Science says global mean sea level rose about 3.3 millimeters per year from 1993 to 2020, which is 30% more than when NASA launched its first satellite mission to measure ocean heights in 1992.
How do scientists track sea level from space?
Satellite altimeters measure the height of the sea surface, and NASA averages that data from a series of satellites that includes TOPEX/Poseidon and the Jason missions. The result is a global mean that does not depend on any single coastline.
NASA Science, in an article dated November 5, 2020, lists the tools it combines to track the causes of the rise:
- Satellites
- Airborne missions
- Shipboard measurements
- Supercomputers
NASA’s sea level portal adds that spaceborne instruments have detected accelerations in ice sheet mass loss and in sea level rise, which is expected when the globe warms. For the wider body of proof that the planet is heating up, read our guide to the evidence of climate change.
Why does local sea level differ from the global average?
The global number is an average, and your coastline can do something quite different. NOAA says that in some ocean basins sea level has risen as much as 6-8 inches (15-20 centimeters) since the satellite record began, partly because winds and currents shift where the ocean stores heat.
The ground matters too. NASA Science notes that the land along coasts is creeping up and down, which changes relative sea level. NOAA lists these local factors:
- Ground settling
- Upstream flood control
- Erosion
- Regional ocean currents
- Land still rebounding or resettling from the weight of vanished Ice Age glaciers
In the United States, NOAA reports that the fastest rates are on the Gulf coast from the mouth of the Mississippi westward, followed by the mid-Atlantic. Only Alaska and a few places in the Pacific Northwest have falling seas, and that will reverse under a pathway with high greenhouse gas emissions, per NOAA Climate.gov.
What does sea level rise mean for people and coasts?
Coasts hold a lot of people. NOAA says almost 30 percent of the U.S. population lives in coastal areas, and that 8 of the world’s 10 largest cities are near a coast, citing the U.N. Atlas of the Oceans.
The first symptom is high-tide flooding, sometimes called nuisance flooding. NOAA reports that it is now 300% to more than 900% more frequent than it was 50 years ago in many U.S. locations, as of its August 2023 page.
Higher background water also lets storm surges reach farther inland. NOAA names the surges tied to Hurricane Katrina, Superstorm Sandy and Hurricane Michael as examples of deadly and destructive events that push farther than they once did.
Other risks listed by NOAA Climate.gov include:
- Roads, bridges, subways, water supplies, power plants and sewage treatment plants
- Coastal ecosystems that give storm protection and fish habitat
- Freshwater aquifers contaminated by saltwater
Flooding is only one of the many effects of climate change that reach people through water, and it is among the easiest to measure.
How high could seas go by 2100?
The answer depends heavily on emissions. NOAA says global mean sea level is likely to rise at least one foot (0.3 meters) above 2000 levels by the end of the century, even on a relatively low emissions pathway.
NOAA’s U.S. scenarios, from its August 2023 page, show how wide the range is:
- Significant emission cuts: U.S. sea level in 2100 around 0.6 meters (2 feet) higher on average than in 2000.
- High emissions with rapid ice sheet collapse: average rise for the contiguous United States of 2.2 meters (7.2 feet) by 2100.
- The same high pathway to 2150: 3.9 meters (13 feet).
These are model projections, not forecasts for a single street. Local land motion and the pace of ice loss will decide the real outcome, so check NOAA Climate.gov and current local guidance for your own coast.
Frequently asked questions
How fast is sea level rising?
Show answer
NASA Science reports about 3.3 millimeters per year from 1993 to 2020, and NOAA reports 3.6 millimeters per year for 2006-2015. Both sit well above the 1.4 millimeters per year of most of the twentieth century, per NOAA Climate.gov and NASA Science.
What causes most sea level rise?
Show answer
Melting glaciers and ice sheets, plus thermal expansion of warming seawater. NASA Sea Level Change gives about 2 mm per year for meltwater and roughly 1 mm per year for expansion.
Is sea level rising at the same rate everywhere?
Show answer
No. Ground settling, currents and land rebound change local rates, and NOAA says that only Alaska and a few places in the Pacific Northwest have falling seas, in its August 2023 page at NOAA Climate.gov.
Will seas keep rising if emissions fall?
Show answer
Most likely, yes. Emission cuts change how much the ocean rises rather than whether it does, since NOAA’s August 2023 page still projects a global gain of at least one foot (0.3 meters) over 2000 levels on a relatively low pathway, per NOAA Climate.gov.
