Frequently Asked Questions

General questions

• Is the rate of sea-level rise increasing?

  Yes. Relying on nearly a 30-year record of satellite measurements, scientists have measured the rate of sea-level rise at 0.13 inches (3.4 millimeters) per year.

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• Are sea levels rising the same all over the world, as if we're filling a giant bathtub?

  No. Sea level rise is uneven, the two main reasons being ocean dynamics and Earth’s uneven gravity field.

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• How does El Niño fit into the sea-level rise picture?

  Over periods of 2-8 years, after removing the overall trend of about 3 millimeters per year, the globally averaged sea-level rise closely follows the waxing and waning of El Niño.

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• How much rise should we expect from Greenland and Antarctica?

  In the future, scientists expect Greenland and Antarctica will contribute larger amounts than current rates. By 2100, the latest estimates of sea level rise contributions from Greenland and Antarctica sum up to about 1 meter (about 3 feet), but totals may be as high as 2 meters (over 6 feet). By 2300, total sea level rise from those ice sheets may be as high as 5 meters (about 16 feet).

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• What causes sea-level rise?

  Most of the observed sea-level rise (about 3 mm per year) is coming from the meltwater of land-based ice sheets and mountain glaciers, which adds to the ocean’s volume (about 2 mm per year combined), and from thermal expansion, or the ocean water’s expansion as it warms (roughly 1 mm per year).

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• How long have sea levels been rising? How does recent sea-level rise compare to that over the previous centuries?

  Between about 21,000 years and about 11,700 years ago, Earth warmed about 4 degrees C (7.2 degrees F), and the oceans rose (with a slight lag after the onset of warming) about 85 meters, or about 280 feet. However, sea levels continued to rise another 45 meters (about 150 feet) after the warming ended, to a total of 130 meters (from its initial level, before warming began), or about 430 feet, reaching its modern level about 3,000 years ago.

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• How much do human activities contribute to sea-level rise?

  Previous estimates show that human activities are responsible for about 70% of the observed sea level rise since 1970, with the percentage approaching 100% as time goes on.

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• Which areas of the world will be most affected by sea-level rise over the next century, and after that?

  Some of the most powerful effects will be seen on flatter coastal land abutting the shallows of large water bodies. If these areas also are prone to landfall by tropical cyclones, the effects will be further intensified. Among the hardest hit will be tropical and sub-tropical river deltas – broad fans of sediment and waterways where rivers meet the sea. Because such deltas often are the sites of port cities, large human populations will be exposed to significantly higher risk. Hot spots include the U.S. East Coast and Gulf Coast, Asia, and islands.

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• How do satellites measure sea-level change?

  Satellite altimetry is all about timing. Sea-surface height can be measured by the time it takes for radar pulses to hit the ocean surface and bounce back to the spacecraft. Laser altimetry works in a similar manner, as laser pulses bounce off land-ice and sea-ice surfaces.

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• Which are more accurate in measuring sea-level rise: tide gauges or satellites?

  Both methods produce accurate results, though they measure different aspects of sea-level rise. Both show, for example, that sea-level rise is accelerating.

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• What is NASA doing to protect its facilities from sea-level rise?

  NASA is taking a multi-pronged approach to protecting its facilities: adapting to rising waters by hardening existing buildings and other structures against flooding, or in some cases relocating structures to safer sites at higher elevations.

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• How do tide gauges measure sea-level change?

  Tide gauges installed along coastlines, or on ocean platforms, rely on sensors to make a continuous record of water height, by the minute, hour, or day. These records are made in comparison to a reference point known as the geoid, or mean (average) sea level and its imagined extension over land areas.

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• How does NASA study sea-level change?

  NASA studies changes in sea-level primarily by using orbiting spacecraft. These satellites capture the changes with altimeters – instruments that rely on radar or laser pulses. These altimetry measurements can be combined with data from coastal tide gauges and from Argo floats, a global network of mobile ocean sensors that move up and down the water column, to provide a fuller picture of sea-level rise.

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More specific questions

• I've heard I won't be able to access data that I used to download through FTP. What happened?

  NASA changed the file transfer protocol, a system for browsing and retrieving data, now in use on the NASA Sea Level Portal. (For example, this applies to those who want to access global mean sea level data on this page.)

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Climate & Data Tools

• What are the scenarios from the Sea Level Rise Interagency Task Force and how do they compare to the projections from the IPCC AR6?

  The scenarios from the Sea Level Rise Interagency Task Force report cover a range of plausible sea level rise by 2100 and beyond. They are derived from and consistent with the projections in the IPCC 6th Assessment Report.

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