Higher “background” water levels mean that deadly and destructive storm surges—like those associated with Hurricane Katrina or “Superstorm” Sandy—push farther inland than they once did.

In urban settings along coastlines around the world, rising seas threaten infrastructure necessary for local jobs and regional industries. Roads, bridges, subways, water supplies, oil and gas wells, power plants, sewage treatment plants, landfills are all at risk from sea level rise.

In the United States, almost 40% of the population lives in relatively high population-density coastal areas, where sea level plays a role in flooding, shoreline erosion, and hazards from storms. Globally, 8 of the world’s 10 largest cities are near a coast, according to the U.N. Atlas of the Oceans.

A decline in water storage on land—aquifers, lakes and reservoirs, rivers, soil moisture—mostly as a result of groundwater pumping, which has shifted water from aquifers to the ocean.

Rising global temperatures results in the volume of water in the ocean expanding as the water warms. This is known as thermal expansion.

Higher sea level also means more frequent “nuisance

flooding”—not deadly or dangerous, usually, but still disruptive and expensive.

In the natural world, rising sea level creates stress on coastal ecosystems that provide recreation, protection from storms, and habitat for fish and wildlife, including commercially valuable fisheries.

Sea level rise at specific

locations may be more or less than the global average due to local factors: subsidence, upstream flood control, erosion, regional ocean currents, and whether the land is still rebounding from the compressive weight of Ice Age glaciers.

Antarctic ice loss more than quadrupled, from 30 gigatons/year between 1992 and 2001 to 147 gigatons/year from 2002 to 2011.

The pace of global sea level rise doubled from 1.7 mm/year throughout most of the twentieth century to 3.4 mm/year since 1993