Higher seas endanger coastal communities—where 40 percent of the world's population lives—and threaten groundwater supplies.
See how sea-level rise from global warming puts New York City at risk—and find other hot spots threatened by rising seas on the Climate Hot Map.
Two major mechanisms are causing sea level to rise. First, shrinking land ice, such as mountain glaciers and polar ice sheets, is releasing water into the oceans. Second, as ocean temperatures rise, the warmer water expands. Trapped within a basin bounded by the continents, the water has nowhere to go but up. In some parts of the world, especially low-lying river deltas, local land is sinking (known as subsidence)—making sea levels that much higher. The consequences of sea level rise include:
- Threats to coastal communities. Some 40 percent of the world's population lives within 62 miles (100 kilometers) of the ocean, putting millions of lives and billions of dollars' worth of property and infrastructure at risk.
- High tides and storm surges riding on ever-higher seas are more dangerous to people and coastal infrastructure.
- Natural protections against damaging storm surges are increasingly threatened. Barrier islands, beaches, sand dunes, salt marshes, mangrove stands, and mud and sand flats retreat inland as sea level rises, unless there are obstructions along the retreat path. If they cannot move, these natural protections are washed over or drowned.
- Many shorelines have sea walls, jetties, and other artificial defenses to protect roads, buildings, and other vital coastal resources. In these areas, sea-level rise increases erosion of stranded beaches, wetlands, and engineered structures
- Saltwater intrusion. Sea-level rise can mean that saltwater intrudes into groundwater drinking supplies, contaminates irrigation supplies, or overruns agricultural fields. Low-lying, gently sloping coastal areas are particularly vulnerable to contamination of freshwater supplies.