Global sea levels are currently rising faster than at any point in at least three millennia, driven primarily by human influence since 1970, according to data compiled by Carbon Brief. World leaders meeting at the UN General Assembly in New York are set to adopt a high-level declaration recognizing these rising seas as an immediate and lived experience rather than a distant scenario, noting that average global ocean levels rose by 20 centimeters between 1901 and 2018.
Cities and Coastal Communities at Acute Risk
Approximately 770 million people, representing 10% of the global population, face acute risks from sea level rise by living less than five meters above the high-tide line, according to a report released by the UN secretary general. Major metropolitan areas including Mumbai and Kolkata in India, alongside Shenzhen and Guangzhou in China, face severe threats from this encroachment.
Higher sea levels intensify persistent flooding, strengthen storm surges, and erode beaches and cliffs. According to Carbon Brief, the frequency of 100-year extreme sea level events has increased 12-fold since 1900. Under a moderate-emissions scenario, these compounding hazards are likely to occur at least annually in many coastal regions by the end of the century. Cities like Jakarta, Indonesia, experience localized sinking of up to 15 centimeters per year over the past decade due to groundwater overextraction, amplifying the local risks beyond climate-driven global averages.
Did you know? Global losses from flooding in the world’s largest 136 coastal cities could reach up to $52 billion per year by 2050—up sharply from $6 billion in 2005—due to continued coastal population growth and development, according to UN findings.
Biodiversity Loss and Coastal Squeeze
Coastal ecosystems face widespread destruction from a dual pressure known as “coastal squeeze,” where human-made structures block wetlands, estuaries, and mangroves from shifting inland as waters rise. According to the 2025 “global wetland outlook” report cited by Carbon Brief, nearly 28 million hectares of coastal wetlands have vanished globally since 1970. In the continental US, only 16% of coastal wetlands are migrating inland at rates fast enough to outpace local sea level rise.
Low-lying islands serving as biodiversity hotspots are particularly vulnerable. A 2013 study modeled that one meter of sea level rise would completely submerge about 6% of island habitat area across 10 biodiversity hotspots, putting dozens of endemic species at risk of extinction. Demonstrating these real-world impacts, researchers documented the first known local extinction of a plant species in the US due to sea level rise in 2024, after hurricanes and saltwater intrusion decimated the Key Largo cactus population.
Small Island Developing States Face Existential Threats
Small island developing states face an acute and disproportionate threat, with many low-lying atolls having average elevations of only one to two meters above sea level, according to the UN. Kiribati lost two small uninhabited islands in 1999, and several uninhabited islands in the Solomon Islands vanished by 2014.
Financial strains compound these geographic vulnerabilities. Small island developing states require up to $6 billion annually by 2035 for climate adaptation, yet received just $1.2 billion in public adaptation finance during 2022-23, according to UN figures.
Coral Reefs and Cultural Heritage Sites in Jeopardy
Cultural heritage sites are similarly imperiled.
Frequently Asked Questions
What are the primary causes of sea level rise?
According to scientific assessments, global sea level rise is driven primarily by the melting of glaciers and ice sheets, the thermal expansion of seawater as oceans absorb heat from global warming, and changes in land-water storage.
How much have global sea levels risen historically?
Global sea levels rose by an average of 20 centimeters between 1901 and 2018, with the rate accelerating significantly in recent decades, adding 10.6 centimeters since 1993 alone, according to Carbon Brief data.
Which cities and populations are most at risk from rising seas?
Approximately 770 million people living less than five meters above the high-tide line face acute risks. Heavily populated coastal cities like Mumbai, Kolkata, Shenzhen, and Guangzhou are among the most vulnerable locations globally.
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