Global sea levels are rising at unprecedented rates, with significant implications for human populations and natural ecosystems. The world’s oceans have risen approximately 20 centimetres since 1901, with the pace of increase accelerating substantially in recent decades—rising 10.6 centimetres since 1993 alone. Scientists attribute this change primarily to human activity, which has been the dominant cause of sea level rise since at least 1970. Under moderate-emissions projections, global average sea levels are expected to rise an additional 56 centimetres by 2100 relative to 1995-2014 baseline measurements.
Approximately 770 million people—roughly 10 percent of the global population—face acute risk from sea level rise, defined as living less than five metres above the high-tide line. This vulnerable population includes residents of major metropolitan areas such as Mumbai, Kolkata, Shenzhen and Guangzhou, as well as entire populations of numerous island nations. The impacts extend beyond direct inundation, as rising seas intensify persistent flooding, strengthen storm surges, erode coastlines and elevate local water tables, increasing flood vulnerability overall. The frequency of extreme sea level events has already increased dramatically, multiplying 12-fold since 1900, with projections suggesting these events could become annual or more frequent in many locations by the century’s end.
Coastal infrastructure faces mounting threats from sea level rise. Critical systems including water supply and wastewater management grow increasingly vulnerable to flooding, potentially severing communities from essential services. Agricultural zones in low-lying areas confront saltwater intrusion risks, while low-income and marginalized populations face disproportionate impacts. Vertical land motion—from subsidence or seismic activity—compounds these dangers; Jakarta exemplifies this challenge, sinking up to 15 centimetres annually due to groundwater extraction.
Despite growing risks, coastal population concentrations continue expanding. Between 2000 and 2018, while global population grew 23 percent, coastal populations within 5 kilometres of shorelines increased 28 percent. This accelerating coastal development threatens economic losses, with projected annual flooding costs in the world’s 136 largest coastal cities potentially reaching $52 billion by 2050, compared with $6 billion in 2005. Communities have implemented various adaptive measures, from Venice’s floodgate system to mangrove restoration and managed retreat strategies, though existing protections may prove insufficient against projected sea level increases.
Coastal ecosystems face rapid degradation from combined development pressures and sea level rise, a phenomenon termed “coastal squeeze.” This process prevents ecosystems from naturally migrating inland, contributing to widespread wetland loss and broader ecological destruction.
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