Is sea level rising?

1. The long-term rise: clear numbers from century-scale records

Tide-gauge reconstructions and historical records show global average sea level has risen roughly 8–9 inches (21–24 cm) since 1880, a baseline widely cited by climate agencies and assessments ^{[1] [4]}, and alternative reconstructions place century-scale rise near 23 cm since 1900 ^[5], underscoring that the upward trend is robust across data sources ^[6].

2. The modern acceleration: what satellites and new studies reveal

Satellite altimetry since 1993 documents a sharp acceleration: global mean sea level rose about 111 mm between 1993 and 2023, with recent studies finding rates more than double those at the start of the satellite era—roughly 4–4.5 mm/yr versus about 2 mm/yr earlier—evidence that the rate of rise has increased in recent decades ^{[2] [3] [6]}. Independent analyses and NASA-led work flagged 2024 as the highest level in decades and reported last year’s increase was around 35% higher than expected, reinforcing the narrative of an accelerating signal ^[7].

3. Why levels are climbing: the physics and main contributors

Two principal processes explain the rise: thermal expansion as warming oceans take up heat and expand, and added water from melting land ice—glaciers and shrinking ice sheets—which together account for the bulk of modern sea-level growth ^{[8] [3]}. Scientists note thermal expansion contributes roughly one-third of contemporary global mean sea level rise, with the remainder coming from land-ice loss and other sources identified in observational budgets ^[3].

4. Regional variation and local impacts: not all coasts feel the same

Global averages mask large regional differences: some basins have risen 15–20 cm since the satellite record began, and local sea level can be higher or lower than the global mean because of ocean currents, winds, land subsidence, groundwater or oil extraction, and post‑glacial rebound—Alaska and parts of the Pacific Northwest, for example, have seen falling local sea level in places even as the global level rises ^{[1] [9]}. Those geographic differences matter: projections suggest about 6 inches globally by 2050 with larger local amounts in some U.S. regions, and hundreds of millions to a billion people live within a few meters of current sea level, amplifying social and economic vulnerability ^{[10] [11]}.

5. Projections, uncertainties, and competing interpretations

Scientists agree future sea-level rise is certain but the magnitude and pace depend on emissions and ice-sheet behavior; ensembles project a wide range by 2100—from roughly 0.28–0.55 m under very low emissions to 0.63–1.02 m under high-emission scenarios—reflecting deep uncertainty about ice-sheet responses ^[5]. This scientific uncertainty fuels competing narratives: recent academic and agency reports document accelerating rise ^{[2] [12]}, while some federal analyses have been interpreted as downplaying acceleration, prompting rebuttals from independent researchers who find doubling of U.S. coastal rates over the last 125 years ^{[13] [14]}. Those disagreements often trace back to methodological choices—time windows, regional versus global focus, and how to treat natural variability—rather than a dispute that sea level is rising.

6. What this means now: planning under acceleration

Because observations show acceleration and because thermal inertia and ice-sheet dynamics imply continued rise through mid-century and beyond, coastal planning must account for faster changes than the twentieth-century pace; agencies and cities are already using satellite and tide-gauge data to inform adaptation even as model projections span a range of outcomes ^{[3] [4]}. Where reporting differs—between conservative federal summaries and some academic findings—the practical takeaway remains that sea level is rising, the rate has increased in recent decades, and impacts will intensify if emissions and ice loss continue ^{[2] [12]}.