Sea level rise threatens homes, infrastructure, and livelihoods around the world. It is the result of global warming, melting glaciers and ice sheets, and thermal expansion of ocean water as it warms. Rising sea levels also increase the intensity of storm surges and coastal flooding, and they contaminate groundwater and soil with salt. More than 30 percent of people worldwide live in coastal areas, and for many of them a rising sea is a real and present danger.
Over the last century, sea levels have risen faster than in any previous period of history. The rate of rise has accelerated since about 1970, when greenhouse gas emissions began to increase.
These trends are reflected in the trajectories of sea level, which were calculated from regional sets of tide gauge observations extrapolated to 2050, adjusted for large-scale natural phenomena like El Nino and the Pacific Decadal Oscillation. The data were then combined with model-based projections to produce a range of possible scenarios for future sea level.
The Earth isn’t really flat, so the effect of gravity subtly pulls more water into some places than others. Tides, ocean currents, and storms also cause local variations in sea levels, making it challenging to hone in on long-term changes. Scientists studying sea levels use data from a variety of sources, including tide stations and satellite laser altimeters. They also analyze sediment and ice cores to learn more about sea levels in the past.