Sea level rise is a change in the height of the ocean’s surface at global and local (relative) levels, caused by various processes such as thermal expansion (water expands as it warms), melting of land-based ice that adds water to the ocean, changes in the shape or amount of the ocean basins, and local land subsidence or uplift. Data on sea level changes are collected from a variety of sources, including tide gauges, coastal buoys, and satellite altimeters.
Sea-level change is a critical climate-change issue. It threatens coastal communities, which make up the majority of U.S. counties, with flooding and erosion that damage roads, buildings, bridges, and other infrastructure. It also threatens natural habitats, including species that live only on islands. And it may lead to a loss of coastal farmland and contaminated freshwater supplies.
There is a direct relationship between climate change and sea level rise: Warmer temperatures cause glaciers and ice sheets to melt, which increases the volume of ocean water. They also cause warmer air to hold more moisture, resulting in more runoff and diminished snowfall, both of which contribute to rising seas.
In addition, sea level rise is accelerated by other climate-change impacts. For example, when warmer waters envelop the Arctic, they push more melting sea ice out of the way. And when a glacier like Pine Island in Antarctica melts, it can speed up the rate of sea-level increase. That is why it’s important to understand the causes and impacts of sea level rise, so that we can prepare for its consequences.