3.2 Global sea level trends

Global sea level trends are a critical aspect of Coastal Resilience Engineering. Historical records, including tide gauges and geological evidence, provide insights into past sea levels, while satellite altimetry offers precise modern measurements. Understanding these trends is crucial for predicting future coastal changes and developing adaptation strategies.

Sea level rise results from complex interactions between oceans, atmosphere, and ice. Thermal expansion of oceans and melting land-based ice are major contributors. Regional variations, caused by factors like vertical land movements and ocean circulation patterns, complicate the global picture. This knowledge is essential for effective coastal management and engineering solutions.

Historical sea level records

• Sea level records provide crucial insights into past climate conditions and help predict future coastal changes in Coastal Resilience Engineering
• Understanding historical sea level trends informs adaptation strategies for coastal communities and infrastructure planning
• Combining multiple data sources enhances the accuracy and reliability of long-term sea level reconstructions

Tide gauge measurements

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  ESSD - North SEAL: a new dataset of sea level changes in the North Sea from satellite altimetry View original

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Top images from around the web for Tide gauge measurements

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  ESSD - North SEAL: a new dataset of sea level changes in the North Sea from satellite altimetry View original

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  Global Warming: How much will sea levels rise in the 21st Century? | Small Epiphanies View original

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  ESSD - North SEAL: a new dataset of sea level changes in the North Sea from satellite altimetry View original

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• Continuous sea level observations recorded by mechanical float gauges since the 18th century
• Network of tide gauges globally measures local sea level changes relative to a fixed point on land
• Longest tide gauge record from Amsterdam dates back to 1700
• Challenges include accounting for vertical land movements and uneven global distribution of gauges

Geological evidence

• Provides sea level data over much longer timescales (thousands to millions of years)
• Includes analysis of coral reefs, marine terraces, and sediment cores
• Microfossils (foraminifera) in sediment cores indicate past sea levels and environmental conditions
• Reconstructs sea level history during past warm periods (interglacials) for comparison with current trends

Satellite altimetry data

• Space-based measurements of global sea surface height since 1992
• Satellites (TOPEX/Poseidon, Jason series) use radar to measure distance between satellite and sea surface
• Provides near-global coverage and high-precision measurements (accuracy of a few centimeters)
• Allows detection of regional variations and short-term fluctuations in sea level

Causes of global sea level rise

• Global sea level rise results from complex interactions between ocean, atmosphere, and cryosphere systems
• Understanding these causes is essential for accurate projections and effective coastal management strategies
• Coastal Resilience Engineering must account for multiple contributing factors to develop comprehensive adaptation plans

Thermal expansion of oceans

• Occurs as seawater warms and increases in volume
• Responsible for about 30-50% of observed global sea level rise since 1971
• Rate of thermal expansion varies with depth and location in the ocean
• Deeper, colder waters expand more than surface waters for the same temperature increase

Melting of land-based ice

• Contributes freshwater to the oceans, raising global sea level
• Major sources include glaciers, ice caps, and ice sheets (Greenland and Antarctica)
• Greenland Ice Sheet loss has accelerated, contributing about 0.7 mm/year to sea level rise
• Antarctic Ice Sheet contribution remains uncertain but potentially significant for future sea level rise

Groundwater extraction vs storage

• Groundwater depletion adds water to the oceans, raising sea level
• Estimated contribution of 0.3-0.4 mm/year to global sea level rise
• Counteracted by increased water storage in artificial reservoirs and dams
• Net effect on sea level depends on balance between extraction and storage over time

Regional variations in sea level

• Sea level changes are not uniform globally, with significant regional differences
• Understanding regional variations crucial for local coastal management and adaptation planning
• Coastal Resilience Engineering must consider site-specific sea level trends for effective design and implementation

Vertical land movements

• Caused by geological processes (tectonics, isostatic rebound) and human activities (subsidence)
• Post-glacial rebound raises land in formerly glaciated regions (Scandinavia, Canada)
• Subsidence in delta regions due to sediment compaction and groundwater extraction
• Can amplify or reduce relative sea level rise at local scales

Ocean circulation patterns

• Influence regional sea level through redistribution of heat and mass
• Changes in major currents (Gulf Stream, Antarctic Circumpolar Current) affect local sea levels
• El Niño-Southern Oscillation (ENSO) causes temporary sea level variations in the Pacific
• Long-term changes in ocean circulation can lead to persistent regional sea level anomalies

Gravitational effects

• Redistribution of mass from melting ice sheets alters Earth's gravitational field
• Leads to lower sea level rise near melting ice sheets and higher rise in distant locations
• Greenland ice loss causes sea level to fall nearby but rise more in the Southern Hemisphere
• Complicates global sea level projections and requires consideration in regional assessments

Observed global sea level trends

• Monitoring global sea level trends essential for understanding climate change impacts on coastal systems
• Observed trends inform policy decisions and adaptation strategies in Coastal Resilience Engineering
• Combining multiple data sources provides a comprehensive picture of past and present sea level changes

20th century rates

• Average rate of global sea level rise during the 20th century estimated at 1.7 mm/year
• Acceleration observed in the latter half of the century
• Tide gauge records show significant spatial and temporal variability
• Reconstruction methods combine tide gauge data with proxy records to estimate global trends

Recent acceleration

• Satellite altimetry reveals global mean sea level rise of 3.3 mm/year since 1993
• Acceleration detected in the altimetry record, with rates increasing to 4.5 mm/year in recent years
• Increased contributions from ice sheet melting and thermal expansion drive acceleration
• Observed acceleration consistent with projections from climate models

Projections for 21st century

• IPCC projects global mean sea level rise of 0.43-0.84 m by 2100 under intermediate emissions scenario
• High-end scenarios suggest potential rise exceeding 1 m by 2100
• Long-term projections indicate continued sea level rise for centuries due to thermal inertia of oceans
• Uncertainties in future emissions and ice sheet dynamics affect projection accuracy

Impacts on coastal systems

• Sea level rise poses significant challenges to coastal environments and human settlements
• Coastal Resilience Engineering focuses on mitigating these impacts through adaptive strategies
• Understanding and quantifying impacts essential for effective coastal management and planning

Coastal erosion and flooding

• Increased wave energy and storm surge heights exacerbate coastal erosion
• Low-lying areas face more frequent and severe flooding events
• Shoreline retreat threatens coastal infrastructure and habitats
• Adaptation measures include beach nourishment, seawalls, and managed retreat

Saltwater intrusion

• Rising sea levels push saltwater further inland in coastal aquifers and estuaries
• Threatens freshwater resources for drinking water and agriculture
• Alters soil chemistry and impacts coastal vegetation
• Mitigation strategies include improved water management and desalination technologies

Ecosystem changes

• Inundation of coastal wetlands and mangroves leads to habitat loss
• Shifts in species distribution and composition of coastal ecosystems
• Coral reefs face increased stress from sea level rise combined with ocean warming and acidification
• Nature-based solutions (living shorelines) can enhance ecosystem resilience to sea level rise

Measurement techniques and technologies

• Accurate and precise measurements crucial for understanding sea level changes
• Advances in technology improve spatial and temporal resolution of sea level data
• Integration of multiple measurement techniques enhances overall understanding of sea level dynamics

Tide gauges vs satellite altimetry

• Tide gauges provide long-term local records but limited spatial coverage
• Satellite altimetry offers near-global coverage but shorter time series
• Combining both methods allows for cross-validation and improved accuracy
• Tide gauges essential for calibrating satellite measurements and studying local effects

GPS and geodetic observations

• GPS measurements track vertical land movements at tide gauge locations
• Improves accuracy of relative sea level trends derived from tide gauges
• Geodetic techniques (VLBI, SLR) provide reference frame for satellite altimetry
• Continuous GPS networks monitor regional land deformation patterns

Gravimetry for mass changes

• GRACE satellite mission measures changes in Earth's gravity field
• Allows estimation of ocean mass changes contributing to sea level rise
• Distinguishes between steric (thermal expansion) and mass-related sea level changes
• Provides insights into ice sheet mass balance and terrestrial water storage variations

Uncertainties and challenges

• Addressing uncertainties crucial for improving sea level projections and risk assessments
• Challenges in sea level science inform research priorities and data collection strategies
• Understanding limitations essential for effective communication of sea level risks to stakeholders

Data quality and coverage

• Historical tide gauge records have varying quality and may contain gaps
• Uneven global distribution of tide gauges limits understanding of regional variations
• Satellite altimetry faces challenges in coastal areas and high latitudes
• Efforts to digitize historical records and expand monitoring networks ongoing

Natural variability vs long-term trends

• Interannual to decadal climate oscillations (ENSO, PDO) influence sea level
• Distinguishing natural variability from anthropogenic trends requires long time series
• Statistical methods (empirical mode decomposition) help separate different timescales
• Understanding natural variability crucial for detecting acceleration in sea level rise

Model limitations

• Climate models struggle to accurately represent all processes affecting sea level
• Ice sheet dynamics and ocean-ice interactions not fully captured in current models
• Uncertainties in future emissions scenarios affect long-term projections
• Ensemble approaches and model intercomparison projects address model limitations

Future scenarios and projections

• Projecting future sea level rise essential for long-term coastal planning and adaptation
• Multiple scenarios consider different emissions pathways and socioeconomic developments
• Coastal Resilience Engineering must account for range of possible future sea level scenarios

IPCC projections

• Latest IPCC report (AR6) provides updated sea level projections
• Likely range of global mean sea level rise by 2100 spans 0.28-1.01 m across scenarios
• Projections include contributions from thermal expansion, glaciers, and ice sheets
• Low-likelihood, high-impact scenarios explore potential for larger rises (up to 2 m by 2100)

Emission scenarios

• Representative Concentration Pathways (RCPs) and Shared Socioeconomic Pathways (SSPs) used
• Range from low-emission (RCP2.6, SSP1-2.6) to high-emission (RCP8.5, SSP5-8.5) scenarios
• Sea level projections vary significantly depending on future greenhouse gas emissions
• Mitigation efforts to reduce emissions can substantially lower long-term sea level rise

Tipping points and thresholds

• Potential for abrupt changes in ice sheet dynamics could lead to rapid sea level rise
• Marine ice sheet instability in West Antarctica represents major tipping point
• Greenland Ice Sheet may have threshold temperature for irreversible melting
• Deep uncertainty surrounds timing and magnitude of potential tipping points

Implications for coastal management

• Sea level rise poses significant challenges for coastal communities and infrastructure
• Coastal Resilience Engineering plays crucial role in developing adaptive management strategies
• Integration of sea level projections into planning and policy essential for long-term resilience

Adaptation strategies

• Range from protection (seawalls, levees) to accommodation (elevated structures) to retreat
• Nature-based solutions (mangrove restoration, living shorelines) gain increasing attention
• Adaptive pathways approach allows flexibility in response to changing sea level conditions
• Cost-benefit analysis helps prioritize adaptation measures based on local context

Infrastructure planning

• Long-lived coastal infrastructure must account for future sea level rise
• Design standards and building codes updated to incorporate sea level projections
• Critical facilities (ports, power plants) require special consideration for resilience
• Green infrastructure approaches complement traditional engineering solutions

Policy and decision-making

• Integration of sea level rise into coastal zone management policies
• Development of risk-based frameworks for assessing and managing coastal hazards
• Challenges in addressing deep uncertainty in long-term sea level projections
• Need for improved communication of sea level risks to policymakers and public

Sea level rise in climate models

• Climate models crucial tools for understanding and projecting future sea level changes
• Continuous improvement in model resolution and process representation
• Integration of sea level components enhances overall climate system understanding

Coupled climate-ice sheet models

• Incorporate dynamic ice sheet models into global climate models
• Improve representation of ice-ocean interactions and ice sheet mass balance
• Allow for feedbacks between climate change and ice sheet evolution
• Enhance ability to project long-term sea level rise under different scenarios

Model validation and improvement

• Comparison of model outputs with observational data (tide gauges, satellites)
• Paleoclimate simulations test model performance under different climate states
• Ongoing efforts to improve representation of key processes (ice shelf melting, ocean eddies)
• Development of high-resolution regional models for better coastal projections

Ensemble projections

• Multiple model runs with varying initial conditions and parameters
• Provide range of possible outcomes and quantify uncertainties
• Multi-model ensembles (CMIP6) combine results from different climate models
• Probabilistic projections inform risk assessment and adaptation planning in coastal areas