Global mean sea level has risen approximately 21 cm since 1900, with the rate of rise accelerating to 3.7 mm per year in the decade ending 2022, according to the IPCC Sixth Assessment Report. What was once a slow, steady process is accelerating as ice sheets in Greenland and Antarctica lose mass faster than projected, putting hundreds of millions of people in low-lying coastal areas at risk.
Sea level rise is the long-term increase in global ocean surface height driven by thermal expansion of warming water and the melting of land-based ice. As one of the 12 physical risk hazards in climate risk assessment, sea level rise determines coastal flood exposure, erosion risk, and the long-term viability of infrastructure near coastlines. Understanding sea level rise projections is essential for coastal planning, insurance, and asset valuation.
What Is Sea Level Rise?
Sea level rise is the increase in the average height of the ocean surface over time. Two distinct processes drive sea level rise, and both are accelerating under climate change.
Sea level rise is not uniform across the globe. Ocean currents, gravitational effects from ice sheet mass loss, and local land subsidence create regional patterns where some coastlines experience sea level rise well above the global average. Parts of the U.S. Gulf Coast and Southeast Asia are seeing rates 2-3 times the global mean due to a combination of ocean dynamics and land subsidence.
Even modest sea level rise has outsized impacts because it raises the baseline from which storm surges and high tides operate. A 0.3-meter rise in sea level does not simply move the waterline inland. It transforms what was a once-in-50-year coastal flood into a once-in-5-year event, fundamentally changing the risk calculus for coastal infrastructure.
What Causes Sea Level Rise?
Three mechanisms contribute to sea level rise, each responding to warming temperatures at different rates:
Thermal expansion. Water expands as it warms. Since the ocean absorbs over 90% of the excess heat trapped by greenhouse gases, the water column is expanding, raising sea levels. Thermal expansion accounts for approximately 40% of observed sea level rise and responds directly to global temperature changes.
Glacier melt. Mountain glaciers and ice caps outside of Greenland and Antarctica are losing mass as temperatures rise. Glacial meltwater flows into the ocean, adding volume. Glacier contributions account for roughly 30% of recent sea level rise. Most mountain glaciers are projected to lose 50-80% of their mass by 2100 under high emissions scenarios, according to NASA.
Ice sheet loss. The Greenland and Antarctic ice sheets contain enough water to raise global sea levels by approximately 65 meters if fully melted. Currently contributing roughly 30% of observed sea level rise, ice sheet loss is the wildcard in projections. Marine-based sections of the West Antarctic Ice Sheet are vulnerable to rapid destabilization, which could accelerate sea level rise beyond current projections.
Sea Level Rise Projections
IPCC AR6 provides sea level rise projections under multiple Shared Socioeconomic Pathway (SSP) scenarios. The projections diverge significantly after mid-century:
| Scenario | Sea Level Rise by 2050 | Sea Level Rise by 2100 | Description |
|---|---|---|---|
| SSP1-2.6 | ~0.15 m | +0.32 m | Low emissions, strong mitigation |
| SSP2-4.5 | ~0.20 m | +0.44 m | Moderate emissions, current trajectory |
| SSP5-8.5 | ~0.25 m | +0.77 m | High emissions, fossil fuel intensive |
By 2050, sea level rise projections across scenarios are relatively similar (0.15-0.25 m) because the ocean’s thermal inertia means near-term rise is largely determined by emissions already in the atmosphere. After 2050, the scenarios diverge dramatically, with SSP5-8.5 producing more than double the sea level rise of SSP1-2.6 by 2100.
These projections do not include potential rapid ice sheet collapse, which could add 0.5 meters or more to 2100 projections. Sea level rise will continue for centuries even after emissions stabilize because thermal expansion and ice sheet response lag behind temperature changes.
How Is Sea Level Rise Risk Assessed?
Sea level rise risk assessment differs from other climate hazards because it uses IPCC AR6 hardcoded projections rather than NASA NEX-GDDP-CMIP6 model outputs. Risk depends on three location-specific factors:
Elevation above sea level. Derived from NASA SRTM (Shuttle Radar Topography Mission) data, elevation determines how much sea level rise a location can absorb before inundation occurs. Low-lying coastal areas below 10 meters elevation face the highest sea level rise risk.
Distance to coast. Locations farther from the coastline are less exposed to direct sea level rise impacts, though they may still face indirect effects through saltwater intrusion into aquifers and changes to river drainage.
Projected sea level rise. The IPCC AR6 projections (SSP2-4.5: +0.44 m, SSP5-8.5: +0.77 m by 2100) provide the magnitude of the hazard. Sea level rise is the only hazard with SSP1-2.6 data available in the assessment framework.
Platforms like Continuuiti combine these factors to rate sea level rise risk on a 5-tier scale, assessed alongside 11 other climate hazards in a complete physical risk profile. The assessment runs across baseline, 2030, 2040, and 2050 time horizons as part of the climate scenario analysis framework.
Coastal Erosion and Adaptation
Sea level rise accelerates coastal erosion by increasing the energy of waves reaching shorelines and reducing the protective buffer of beaches and dunes. Adaptation strategies fall into three categories:
Protection. Sea walls, levees, and storm surge barriers defend existing coastal development. Effective but expensive, engineered defenses are the primary response for high-value urban areas and critical infrastructure.
Accommodation. Elevating structures, improving drainage systems, and flood-proofing buildings allow continued use of coastal areas while accepting periodic flooding. Building codes in sea level rise-exposed areas increasingly require elevated foundations.
Managed retreat. Relocating communities and infrastructure away from the coast is the most effective long-term response but faces significant social and political barriers. Several island nations and low-lying communities are already planning or executing managed retreat as sea level rise makes current locations unviable.
Frequently Asked Questions
What causes sea level rise?
Sea level rise is caused by thermal expansion of warming ocean water (about 40%), melting mountain glaciers (about 30%), and Greenland/Antarctic ice sheet loss (about 30%). All three mechanisms are accelerating under climate change.
How much will sea levels rise by 2050?
IPCC projections show approximately 0.15-0.25 meters of sea level rise by 2050, with modest differences between scenarios. Near-term rise is largely locked in by emissions already in the atmosphere.
How much will sea levels rise by 2100?
Under moderate emissions (SSP2-4.5): +0.44 meters. Under high emissions (SSP5-8.5): +0.77 meters. Rapid ice sheet collapse could add significantly more. Sea level rise continues for centuries after emissions stabilize.
How is sea level rise risk assessed?
Sea level rise risk combines IPCC AR6 projections with location-specific elevation (NASA SRTM) and distance to coast. Low-lying areas below 10 meters face the highest risk. It is the only hazard using IPCC hardcoded values rather than NASA GDDP model outputs.
Is sea level rise the same everywhere?
No. Regional variation is significant due to ocean currents, gravitational effects, and land subsidence. Some coastlines experience rates 2-3 times the global average, making location-specific assessment essential.
Sea level rise is the most irreversible of the 12 physical climate hazards. Once sea levels rise, they do not recede on human timescales. Assessing sea level rise risk through the combination of elevation, coastal proximity, and IPCC projections identifies which locations face growing inundation and erosion exposure over the coming decades.
