Sea Level Rise
Global mean sea level has risen approximately 21–24 cm since 1880. The rate has accelerated from ~1.4 mm/year in the early 20th century to ~4.5 mm/year in the most recent decade. IPCC projections through 2100 range from ~30 cm (low emissions, low ice-sheet contribution) to over 1 metre (high emissions, possible Antarctic instability).
Key insights
Three sources, accelerating contributions
Sea level rises from three main sources: thermal expansion of warming seawater (~40% of recent rise), glacier melt (~25%), and ice-sheet melt from Greenland (~21%) and Antarctica (~14%). Through ~2000 thermal expansion dominated; since then glacier and ice-sheet melt has grown faster. The acceleration is from the cryospheric contributions, not thermal expansion.
The Atlantic and Pacific are not rising at the same rate
Local sea-level rise varies substantially around the global mean. The US East Coast, parts of the Caribbean, and the Indian Ocean have risen faster than average. The Pacific North-West coast has risen more slowly because of local oceanographic and gravitational effects (ice-sheet mass loss reduces gravitational pull on nearby ocean water, raising distant water more). Vertical land motion (subsidence in deltas, post-glacial uplift in Scandinavia) further modifies local rates.
The long tail is the hard part
Even if emissions stopped today, sea level would continue to rise for centuries because the deep ocean continues to warm and the ice sheets respond slowly. Committed multi-metre rise is locked in by past warming on millennial timescales. The 2100 projection bands narrow considerably; the 2300 bands span 0.5 m to 6+ m depending on Antarctic-ice-sheet response. Most of the 21st-century damage is from 'where exactly' coastal flooding hits, not whether it happens.
Global mean sea level 1880–2024
mm change relative to 1993–2008 mean
Key Finding: Continuous rise with clear post-1990 acceleration. The IPCC AR6 confirms ongoing acceleration through 2024.
Sources of recent sea level rise (2006–2018 average)
mm/year contribution by source
Key Finding: Thermal expansion is no longer the dominant source. Ice sheets and glaciers now drive most of the rise.
Methodology & caveats
Satellite altimetry since 1993
TOPEX/Poseidon (1992–2006) and subsequent Jason satellites (Jason-1, -2, -3, Sentinel-6) provide a continuous global sea-level record since 1993 with ~0.5 mm/year precision. The satellite record is concatenated with tide-gauge records back to ~1880. Pre-1880 reconstructions use coral, salt marsh and isotope proxies and are less precise.
Eustatic vs relative sea level
Eustatic (global mean) sea level is what altimetry measures. Relative sea level, what coastal communities experience, equals eustatic plus local vertical land motion. Subsiding deltas (Mississippi, Mekong, Nile, Bangladesh) experience relative rise much faster than global mean. Uplifting coasts (Scandinavia, Alaska, parts of New Zealand) experience less or even falling relative sea level.
Antarctic instability
The largest uncertainty in 21st-century projections is the West Antarctic Ice Sheet. Marine-terminating glaciers (Thwaites, Pine Island) sit on bedrock below sea level and may be subject to marine ice-sheet instability — a process that, if triggered, can produce metres of rise on multi-century timescales. Current evidence suggests Thwaites is destabilising; how fast remains the biggest open scientific question.