Causes of Sea Level Rise: Thermal Expansion, Ice Melt, Land Water Loss, Ocean Dynamics

Global sea level has risen ~20–25 cm (8–10 inches) since 1900, accelerating to ~3.4 mm/yr (satellite era). Four primary drivers:

1. Thermal Expansion (Thermosteric Rise) — ~40–50%

Oceans absorb >90% of excess heat from greenhouse warming. Water expands as it warms—basic physics. Upper 700m accounts for most; deep ocean contributes increasingly.

2. Land Ice Melt (Barystatic Rise) — ~40–50%

Greenland Ice Sheet: ~270 Gt/yr loss (surface melt + iceberg calving). Antarctic Ice Sheet: ~150 Gt/yr (West Antarctic collapse risk). Glaciers worldwide: ~220 Gt/yr. Total: ~640 Gt/yr → ~1.8 mm/yr sea level equivalent.

3. Terrestrial Water Storage Decline — ~10–15%

Groundwater depletion (irrigation > recharge) → water reaches ocean. Reservoir impoundment (dams) partially offsets—but net loss dominates. Wetland drainage, deforestation reduce land storage.

4. Ocean Dynamic Changes — Regional, Not Global

Circulation shifts (AMOC slowdown) redistribute water—US East Coast sees amplified rise. Wind pattern changes pile water regionally. Gravitational/rotational effects from ice mass loss create "fingerprints"—sea level falls near melting ice, rises farther away.

Future Projections

IPCC AR6 (2100, SSP5-8.5): 0.63–1.01 m. Low-confidence high-end: >2 m (ice sheet instability). Commitment: Centuries of rise even if emissions stop—ocean/ice inertia.

Sea level rise is measured, attributed, accelerating, and committed. The causes are known; the response is the challenge.