Global sea levels are rising at unprecedented rates, with oceans having climbed approximately 20 centimetres between 1901 and 2018. Since 1993, the rate has accelerated markedly, with ocean levels rising 10.6 centimetres over that three-decade span. Scientists attribute this phenomenon primarily to human activities, which have been the dominant cause of sea level rise since at least 1970. The rise results from multiple factors, including glacial and ice sheet melting, thermal expansion of warming seawater, and changes in land-water storage systems.
According to UN analysis released last month, 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 high-tide lines. This population includes residents of major metropolitan centres such as Mumbai, Kolkata, Shenzhen, and Guangzhou, as well as entire populations of numerous island nations. Under moderate-emissions projections, global average sea level is expected to rise an additional 56 centimetres by 2100 relative to 1995-2014 baseline measurements.
The consequences of rising seas extend across multiple domains. Coastal communities face increased persistent flooding, intensified storm surges, beach and cliff erosion, and rising water tables that amplify flood vulnerability. The frequency of extreme sea level events—where high tides, storm surges, and relative sea level rise combine—has increased 12-fold since 1900 and is projected to occur annually or more frequently in many locations by century’s end. Critical infrastructure including water systems and wastewater management facilities faces growing inundation risks, with low-income and marginalised populations experiencing disproportionate impacts. Saltwater intrusion threatens agricultural production in low-lying coastal areas, while vertical land motion in locations like Jakarta, Indonesia, can amplify relative sea level rise beyond climate-driven contributions.
Despite escalating risks, coastal population growth continues accelerating. Between 2000 and 2018, global population increased by slightly over 23 percent, while coastal populations within 5 kilometres of shorelines grew 28 percent. Projected annual flooding losses in 136 major coastal cities could reach $52 billion by 2050, compared to $6 billion in 2005. Communities have implemented various adaptive measures, from Venice’s floodgate system deployed in October 2020 and activated 48 additional times subsequently, to seawalls, ecosystem restoration, and managed relocation. However, existing protections may prove insufficient, potentially being breached 10 times more frequently over the next 30 years under low-emissions scenarios. Coastal ecosystems face destruction through development and sea level rise interactions termed “coastal squeeze,” where ecosystems unable to migrate inland due to human structures face widespread loss.
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