Sea level rise

**Sea Level Rise Observations and Measurements**:
– Global mean sea level rose by about 20cm (7.9in) between 1901 and 2018.
– Satellite radar measurements found a rise of 7.5cm (3.0in) from 1993 to 2017.
– Sea level rise accelerated to 4.62mm (0.182in)/yr for 2013–2022.
– Tide gauges measure relative sea level, while satellites measure absolute sea level changes.
– Researchers consider ongoing deformations of the solid Earth for precise measurements.
– Variations in water, changes in volume, and land elevation drive sea level changes.
– Different techniques used to measure sea level include tide gauges and satellites.
– Tide gauges have spatial gaps but cover a longer period than satellites.
– Tide gauge data combined with satellite data showed a rise in global mean sea level.
– Satellites use microwave pulses to measure distance to the sea surface.
– Satellite data estimated sea level rise at 3.0±0.4 millimeters per year from 1993 to 2017.
– Altimetric satellites record sea level changes since 1992.

**Regional Variations and Causes of Sea Level Rise**:
– Sea level rise varies globally due to factors like subsidence and post-glacial rebound.
– Melting ice affects gravitational pull, causing regional sea level variations.
– The Atlantic warming faster than the Pacific impacts sea levels differently.
– Land subsidence contributes to higher relative sea level rise in delta regions.
– Human activities like extraction of groundwater contribute to subsidence and affect sea levels.
– Earth lost 28 trillion tonnes of ice between 1994 and 2017.
– Warming causes sea level rise through ocean expansion and melting ice sheets.
– Glacier retreat and ocean expansion have dominated sea level rise.
– Ice loss rate has increased by 57% since the 1990s.
– Glacier losses are partially offset by snowfall.

**Impacts and Adaptation Strategies for Sea Level Rise**:
– Rising seas lead to flooding, storm surges, and tsunamis affecting coastal populations.
– Coastal ecosystems like mangroves are at risk due to sea level rise.
– Sea level rise will expose millions to annual flooding by 2050 without emission reductions.
– Vulnerability to sea level rise varies based on local factors like tidal range.
– Countries in Asia like Bangladesh and Indonesia are highly exposed to sea level rise.
– Societies can adapt to sea level rise through managed retreat, coastal accommodation, or protection measures.
– Adaptation strategies may need to be tailored based on population growth in vulnerable areas.
– Poorer nations face challenges in implementing adaptation approaches.
– Coastal ecosystems adapt by moving inland, but barriers may hinder this process.
– Adaptation choices should consider a combination of hard and soft approaches for effective mitigation.

**Sea Level Rise Projections and Expert Estimates**:
– NOAA predicts varying sea level rise levels through 2050 for different US coastlines.
– Process-based modeling combines physical processes to predict sea level rise.
– Semi-empirical techniques use historical data to model sea level rise responses to warming.
– Different modeling approaches provide insights into future sea level rise scenarios.
– A 2020 survey of 106 experts estimated a median sea level rise of 45cm by 2100 for RCP2.6.
– Experts estimated a median sea level rise of 93cm by 2100 for RCP8.5.
– NOAA suggested a 50% probability of 0.5m sea level rise by 2100 under 2°C warming.
– Year 2019 elicitation predicted sea level rise of 30cm by 2050 and 70cm by 2100 in low emission scenarios.
– Experts estimated a small chance of sea levels exceeding 1 meter by 2100 even in low emission scenarios.

**Antarctic Ice Loss and Long-Term Sea Level Rise Predictions**:
– Antarctica’s ice loss contributes significantly to uncertainties in future sea level projections.
– West Antarctica’s contribution to global sea levels has accelerated since the 21st century.
– The collapse of key glaciers in West Antarctica could lead to significant sea level rise.
– Most studies indicate that the East Antarctic Ice Sheet (EAIS) is still gaining mass.
– Some East Antarctica glaciers have lost ice due to ocean warming and declining sea ice support.
– Studies estimate different scenarios for sea level rise due to Antarctic ice loss.
– Median projections suggest a rise of 16cm to 37cm by 2300 under varying emission scenarios.
– Models suggest sea level rise will continue for centuries even if temperatures stabilize.
– Tipping points of Greenland and Antarctica ice sheets could significantly impact long-term sea level rise.
– Continued carbon dioxide emissions could lead to tens of meters of sea level rise over millennia.