---
source: https://iinventedlight.com/library/notes/sea-level-rise.md
title: "Is sea level rising, and why?"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "US government work, public domain; restated in our own words"
attribution: "Summary by iinventedlight (AI-assisted). Sources: NASA, Climate Change: Global Sea Level, US government work, public domain; NASA, Is sea level rising?, US government work, public domain."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-04
status: published
checked_on: 2026-11-04
as_of: 2026-11-04
confidence: medium
untested: "No observation or experiment was done; only the fetched government pages were read."
category: coverage-gaps
topic_area: "science-explain: earth and ocean science"
tags: science, ocean, sea-level, climate
sources:
  - id: S1
    title: "Climate Change: Global Sea Level"
    publisher: NASA
    url: https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level
    accessed: 2026-11-04
    license: "US government work, public domain"
  - id: S2
    title: "Is sea level rising?"
    publisher: NASA
    url: https://oceanservice.noaa.gov/facts/sealevel.html
    accessed: 2026-11-04
    license: "US government work, public domain"
---
# Is sea level rising, and why?

## Short answer
Yes. Global average sea level has risen about 8 to 9 inches (21 to 24 cm) since 1880, and the rate is speeding up. The two main causes are ocean water expanding as it warms and melting land ice such as glaciers and ice sheets. [S1][S2]

## Key points
- The yearly rise has more than doubled, from about 1.4 mm in most of the 20th century to about 3.6 mm more recently. [S1]
- Sea level is measured with tide stations (local) and satellite altimeters (global). [S2]
- Along much of the U.S. coast, local rise is faster than the global average because land is sinking. [S1]
- Higher seas let storm surge reach farther inland and bring more nuisance flooding. [S2]

## Claims
- id: C1
  claim: Global average sea level has risen 8-9 inches since 1880.
  source: S1
  evidence: "Global average sea level has risen 8–9 inches (21–24 centimeters) since 1880."
- id: C2
  claim: The rate of global sea level rise is accelerating.
  source: S1
  evidence: "The rate of global sea level rise is accelerating"
- id: C3
  claim: Thermal expansion and melting land ice are the two major causes.
  source: S2
  evidence: "The two major causes of global sea level rise are thermal expansion"
- id: C4
  claim: Sea level is measured with tide stations and satellite altimeters.
  source: S2
  evidence: "Sea level is primarily measured using tide stations and satellite laser altimeters."

## Sources
- [S1] Climate Change: Global Sea Level. NASA. https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level . License: US government work, public domain. Accessed 2026-11-04.
- [S2] Is sea level rising?. NASA. https://oceanservice.noaa.gov/facts/sealevel.html . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).