Sea level rise sounds simple, but it is driven by two distinct physical processes working together.
Knowing which is which explains both how fast seas are rising and why the pace keeps accelerating.
TL;DR
- Global sea level has risen about 8 to 9 inches, or 21 to 24 centimeters, since 1880.
- In recent years, roughly two-thirds of the rise came from melting ice sheets and glaciers, and about one-third from thermal expansion as seawater warms.
- Since 1993, the annual rate of rise has more than doubled.
The sea level figures here come from NASA’s Sea Level Change Portal and NOAA.
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The two drivers of rising seas
| wdt_ID | wdt_created_by | wdt_created_at | wdt_last_edited_by | wdt_last_edited_at | Driver | Contribution | Mechanism |
|---|---|---|---|---|---|---|---|
| 1 | emmanuel-ashemiriogwa | 06/08/2026 05:50 PM | emmanuel-ashemiriogwa | 06/08/2026 05:50 PM | Melting ice sheets and glaciers | ~2/3 | Adds water to the ocean |
| 2 | emmanuel-ashemiriogwa | 06/08/2026 05:50 PM | emmanuel-ashemiriogwa | 06/08/2026 05:50 PM | Thermal expansion | ~1/3 | Warm water takes up more space |
| 3 | emmanuel-ashemiriogwa | 06/08/2026 05:50 PM | emmanuel-ashemiriogwa | 06/08/2026 05:50 PM | Land water storage | small | Dams, aquifers, rainfall shifts |
Most of the observed rise, about 3 millimeters per year, comes from meltwater adding to the ocean’s volume, plus thermal expansion as the water warms.
The balance between the two shifts year to year.
In 2024, the contributions flipped, with two-thirds of the rise coming from thermal expansion, driven by unusual ocean warming.
Why the pace keeps accelerating
The engine behind both drivers is the same: heat.
As the planet warms, more ice melts, and the ocean expands faster, so the rate itself increases.
The Antarctic Ice Sheet lost 4,876 gigatonnes of ice between 1979 and 2024, with losses steadily accelerating, and Greenland has lost mass every single year since 1996.
This is why sea level rise is not a steady line but a curve bending upward.
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Where this matters for the U.S. and UK
Sea level at U.S. coastlines is expected to rise on average between 10 and 12 inches over the next three decades.
Low-lying U.S. cities, the UK’s coastal towns, and Canada’s Atlantic and Arctic coasts all face rising baselines that turn ordinary storms into flooding events.
Around 900 million people worldwide live in low-lying coastal zones, and the wealthy coastlines of the core markets are not exempt.
The physics that raises the sea in Bangladesh raises it in Florida too.
ELI5
The sea is rising for two reasons: ice on land is melting and adding water to the ocean, and the ocean water itself expands as it warms up. Both are caused by the planet getting hotter, and both are speeding up.
Sources
NASA | NASA JPL | Climate.gov
