3.1 Causes of sea level rise
9 min read•august 21, 2024
Sea level rise is a complex phenomenon with multiple causes. of oceans, melting land-based ice, and vertical land movements are key factors driving global and regional changes in sea levels.
Atmospheric and oceanic circulation patterns, gravitational effects, and human activities also play significant roles. Climate change amplifies these processes, creating challenges for coastal communities and necessitating adaptive engineering solutions.
Thermal expansion of oceans
- Thermal expansion of oceans plays a crucial role in sea level rise, impacting coastal resilience engineering strategies
- Understanding this process helps engineers develop adaptive measures for coastal communities and infrastructure
Heat absorption by oceans
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- Oceans absorb over 90% of excess heat in Earth's climate system
- Increased atmospheric trap more heat, leading to warmer oceans
- Heat absorption varies with depth, with surface waters warming faster than deeper layers
- Thermal inertia of oceans causes delayed response to atmospheric temperature changes
Volume increase of water
- Water molecules expand as temperature increases, occupying more space
- Expansion coefficient of seawater varies with temperature, salinity, and pressure
- Volume increase contributes to approximately 30-50% of observed global sea level rise
- Thermal expansion affects entire water column, not just surface layers
Regional variations
- Thermal expansion impacts differ across ocean basins due to circulation patterns
- Western boundary currents (Gulf Stream) experience higher rates of thermal expansion
- Shallow coastal areas may see more rapid sea level rise from thermal expansion
- Deep ocean warming contributes to long-term sea level rise trends
Melting of land-based ice
- Land-based ice melt significantly contributes to global sea level rise, posing challenges for coastal resilience
- Engineers must consider the long-term impacts of ice melt when designing coastal protection measures
Glaciers and ice sheets
- Glaciers store approximately 70% of Earth's freshwater
- Ice sheets in Greenland and Antarctica contain vast amounts of frozen water
- Melting occurs through surface ablation and calving of ice into the ocean
- Rate of glacier retreat has accelerated in recent decades due to climate change
Greenland vs Antarctica
- Greenland Ice Sheet loses mass primarily through surface melting and runoff
- experiences mass loss mainly through ice shelf collapse and glacier acceleration
- Greenland contributes more to current sea level rise, but Antarctica poses greater long-term risk
- West Antarctic Ice Sheet considered potentially unstable due to marine ice sheet instability
Meltwater contribution
- Meltwater from land ice directly adds volume to the oceans
- Contribution varies annually based on seasonal melting patterns
- Accelerating melt rates increase the rate of sea level rise
- Meltwater alters local ocean salinity, potentially affecting circulation patterns
Vertical land movements
- Vertical land movements impact relative sea level changes, crucial for coastal resilience engineering
- Understanding these processes helps in developing localized adaptation strategies for coastal areas
Isostatic rebound
- Post-glacial rebound occurs as land rises after removal of ice sheet weight
- Affects regions previously covered by ice sheets during last glacial maximum
- Can cause relative sea level fall in some areas (Scandinavia) and rise in others (US East Coast)
- Rates of vary from millimeters to centimeters per year
Tectonic plate shifts
- Plate tectonics cause vertical land movements through uplift and subsidence
- Subduction zones experience complex patterns of land level changes
- Earthquakes can cause sudden vertical displacements affecting local sea levels
- Long-term tectonic movements influence regional sea level trends
Subsidence due to extraction
- Groundwater and hydrocarbon extraction cause land subsidence
- Coastal cities (Jakarta, New Orleans) experience accelerated relative sea level rise due to subsidence
- Compaction of sediments in river deltas contributes to local land sinking
- Subsidence rates can exceed global sea level rise in some areas, exacerbating flood risks
Atmospheric and oceanic circulation
- Atmospheric and oceanic circulation patterns significantly influence regional sea level variations
- Coastal resilience engineers must account for these dynamic systems in their designs and projections
Wind patterns and currents
- Trade winds and westerlies affect ocean surface currents and sea level distribution
- Ekman transport causes water to pile up or be pushed away from coasts
- Western boundary currents (Gulf Stream, Kuroshio) influence regional sea levels
- Changes in circulation patterns can lead to local sea level rise or fall
El Niño and La Niña effects
- El Niño events cause higher sea levels in the eastern Pacific and lower in the western Pacific
- La Niña produces opposite effects, with higher sea levels in the western Pacific
- These oscillations can cause temporary sea level changes of up to 20-30 cm
- Frequency and intensity of ENSO events may change with climate change, affecting sea level patterns
Gulf Stream variations
- Gulf Stream transports warm water northward along the US East Coast
- Weakening of the Gulf Stream can lead to higher sea levels along the US Atlantic coast
- Climate change may affect the strength and position of the Gulf Stream
- Changes in this current system have implications for coastal flooding and erosion risks
Gravitational effects
- Gravitational effects play a crucial role in regional sea level variations, impacting coastal resilience strategies
- Engineers must consider these complex interactions when assessing long-term sea level rise projections
Ice mass loss impacts
- Large ice masses exert gravitational pull on surrounding ocean waters
- As ice sheets melt, their gravitational influence decreases
- Counterintuitively, sea levels may fall near melting ice sheets due to reduced gravitational pull
- Areas far from melting ice sheets experience higher than average sea level rise
Redistribution of water
- Melting ice sheets cause changes in Earth's rotation and gravitational field
- Water redistributes across the globe in response to these changes
- Equatorial regions may experience higher sea level rise due to redistribution
- Complex patterns of sea level change emerge from the interplay of gravitational effects
Regional sea level fingerprints
- Each ice sheet and glacier system produces a unique pattern of sea level change
- Greenland ice loss affects sea levels differently than Antarctic ice loss
- Fingerprints help identify the source of observed sea level changes
- Understanding fingerprints improves projections of future regional sea level rise
Human activities
- Human activities directly and indirectly influence sea level rise, presenting challenges for coastal resilience engineering
- Recognizing and mitigating these anthropogenic factors is crucial for sustainable coastal management
Groundwater depletion
- Excessive groundwater extraction transfers water from land to oceans
- Contributes to global sea level rise by adding water volume to oceans
- Causes land subsidence, exacerbating local relative sea level rise
- Particularly significant in arid regions and heavily populated coastal areas
Dam construction impacts
- Large-scale dam construction has temporarily slowed sea level rise
- Reservoirs store water on land, reducing the volume reaching oceans
- Effect is diminishing as new dam construction slows and reservoirs fill with sediment
- Future dam removal could release stored water, potentially accelerating sea level rise
Coastal development consequences
- and land reclamation alter natural coastal processes
- Destruction of coastal ecosystems (mangroves, salt marshes) reduces natural buffers against sea level rise
- Coastal infrastructure can disrupt sediment transport, affecting local erosion and accretion patterns
- Hard engineering solutions may exacerbate erosion in adjacent areas, leading to increased vulnerability
Climate change factors
- Climate change significantly influences sea level rise, presenting complex challenges for coastal resilience engineering
- Understanding these factors is essential for developing adaptive strategies and long-term coastal management plans
Greenhouse gas emissions
- Increased atmospheric CO2 and other greenhouse gases trap heat in Earth's system
- Higher temperatures lead to thermal expansion of oceans and accelerated ice melt
- Different emission scenarios result in varying projections of future sea level rise
- Mitigation efforts to reduce emissions can slow the rate of sea level rise in the long term
Feedback loops
- Positive feedback mechanisms amplify the effects of initial warming
- Albedo feedback: melting ice exposes darker surfaces, absorbing more heat
- Permafrost thaw releases methane, a potent greenhouse gas
- Ocean acidification may affect marine ecosystems, indirectly impacting sea level through food web changes
Tipping points in climate systems
- Critical thresholds beyond which rapid and irreversible changes occur
- Potential collapse of West Antarctic Ice Sheet could lead to several meters of sea level rise
- Shutdown of Atlantic Meridional Overturning Circulation would affect regional sea levels
- Abrupt changes in climate systems pose significant challenges for coastal adaptation planning
Temporal variations
- Understanding temporal variations in sea level is crucial for coastal resilience engineering and risk assessment
- Engineers must consider both short-term fluctuations and long-term trends when designing coastal protection measures
Short-term vs long-term changes
- Short-term changes include tides, storm surges, and seasonal variations
- Long-term changes reflect climate-driven sea level rise and geological processes
- Combination of short-term and long-term changes determines flood risk and
- Coastal infrastructure must be designed to withstand both immediate and future sea level conditions
Seasonal and annual fluctuations
- Seasonal cycles caused by changes in temperature, wind patterns, and ocean currents
- Annual variations influenced by climate phenomena (El Niño, North Atlantic Oscillation)
- Steric effects due to thermal expansion and salinity changes contribute to annual cycles
- Understanding these fluctuations improves flood forecasting and coastal management
Historical sea level trends
- Geological evidence shows sea levels have varied by over 100 meters in Earth's history
- Rate of sea level rise has accelerated since the Industrial Revolution
- 20th century saw average sea level rise of 1.7 mm/year
- Current rate of global mean sea level rise exceeds 3 mm/year, with further acceleration expected
Measurement and monitoring
- Accurate measurement and monitoring of sea level changes are essential for coastal resilience engineering
- Multiple techniques provide comprehensive data for understanding past, present, and future sea level trends
Satellite altimetry techniques
- Satellites measure sea surface height with millimeter-level precision
- Global coverage allows for monitoring of open ocean and coastal areas
- Continuous measurements since 1992 provide crucial data on sea level trends
- Challenges include correcting for atmospheric effects and satellite orbit variations
Tide gauge networks
- Long-term records from tide gauges provide historical sea level data
- Coastal locations offer insights into local relative sea level changes
- Global network of tide gauges allows for regional and global trend analysis
- Limitations include uneven global distribution and land movement effects
Geological evidence interpretation
- Proxy records (coral reefs, sediment cores) provide insights into past sea levels
- Tree rings and ice cores offer information on past climate conditions
- Archaeological evidence of coastal settlements indicates historical sea levels
- Combining multiple lines of evidence improves understanding of long-term sea level trends
Regional differences
- Regional variations in sea level rise present unique challenges for coastal resilience engineering
- Understanding local factors is crucial for developing effective adaptation strategies
Hotspots of sea level rise
- Certain regions experience faster than average sea level rise
- Western Pacific shows higher rates due to wind-driven water redistribution
- US East Coast faces accelerated rise from land subsidence and ocean dynamics
- Identifying hotspots helps prioritize adaptation efforts and resource allocation
Coastal geometry influence
- Shape and bathymetry of coastlines affect local sea level changes
- Shallow continental shelves may experience amplified sea level rise
- Narrow bays and estuaries can amplify tidal ranges and storm surges
- Complex coastlines require detailed modeling to assess future flood risks
Local vs global sea level rise
- Global mean sea level rise differs from local relative sea level changes
- Vertical land movements cause divergence between local and global trends
- Ocean dynamics and gravitational effects create spatial variations in sea level rise
- Coastal communities must focus on local relative sea level rise for adaptation planning
Key Terms to Review (18)
Adaptation measures: Adaptation measures are strategies and actions taken to adjust to the impacts of climate change, particularly in response to the effects of sea level rise. These measures aim to minimize vulnerability and enhance resilience in communities, ecosystems, and economies facing changing environmental conditions. Effective adaptation involves understanding the specific risks posed by climate change and implementing tailored solutions to address those risks.
Antarctic Ice Sheet: The Antarctic Ice Sheet is a massive layer of ice covering the continent of Antarctica, consisting of two main components: the East Antarctic Ice Sheet and the West Antarctic Ice Sheet. This ice sheet contains about 60% of the world's fresh water and plays a crucial role in regulating global sea levels. As climate change accelerates, understanding its stability and potential contributions to sea level rise becomes increasingly important.
Carbon emissions: Carbon emissions refer to the release of carbon dioxide (CO2) and other carbon compounds into the atmosphere, primarily as a result of human activities such as burning fossil fuels, deforestation, and industrial processes. These emissions are significant contributors to climate change, as they increase the concentration of greenhouse gases in the atmosphere, leading to global warming and sea level rise.
Coastal Erosion: Coastal erosion is the process by which coastlines are eroded and reshaped by the action of waves, currents, tides, and human activity. This natural process is influenced by various factors, including sediment transport and sea level changes, which can significantly impact coastal landforms and ecosystems.
Deforestation: Deforestation is the large-scale removal of trees from forested areas, leading to significant environmental changes. This process can disrupt ecosystems, contribute to climate change by increasing carbon dioxide levels, and result in loss of biodiversity. Deforestation is closely linked to rising sea levels and the health of coastal ecosystems, particularly mangrove forests, which play a crucial role in protecting shorelines and supporting marine life.
Glacial melt: Glacial melt refers to the process by which glaciers and ice sheets lose mass as ice transforms into water, primarily due to rising global temperatures. This phenomenon contributes significantly to sea level rise and is a key indicator of climate change, impacting global sea level trends and coastal environments.
Greenhouse gases: Greenhouse gases are atmospheric gases that trap heat from the Earth's surface, contributing to the greenhouse effect. This effect is essential for maintaining the Earth's temperature, but an excess of these gases, primarily due to human activities, leads to global warming and climate change, which significantly impacts sea levels.
Greenland Ice Cap: The Greenland Ice Cap is the second largest ice body in the world, covering approximately 1.7 million square kilometers of Greenland's land surface. It plays a crucial role in global sea level rise, as its melting contributes significantly to the overall increase in ocean levels due to climate change and global warming.
Isostatic rebound: Isostatic rebound refers to the process of land rising after being compressed by the weight of glaciers and ice sheets. This phenomenon occurs as the Earth's crust adjusts to changes in weight, particularly following the melting of large ice masses, which can result in significant elevation changes in coastal and inland areas. Understanding isostatic rebound is essential for comprehending the broader impacts of climate change on sea level rise and land stability.
James Hansen: James Hansen is a prominent American climate scientist known for his research on climate change and advocacy for policies to address global warming. His work has been instrumental in raising awareness about the impact of human activities on the climate system and understanding the causes of sea level rise, making him a significant figure in discussions surrounding environmental science and policy.
Millimeters per year: Millimeters per year is a unit of measurement that quantifies the rate of change in elevation or sea level over time, specifically indicating how many millimeters the level rises or falls annually. In the context of sea level rise, this measurement is crucial for understanding the impact of climate change, as it helps scientists and policymakers assess trends in rising waters due to melting ice caps and thermal expansion of seawater.
Mitigation strategies: Mitigation strategies refer to approaches and actions taken to reduce or prevent the impacts of environmental challenges, such as erosion and sea level rise. These strategies can include both engineering solutions, like coastal barriers and seawalls, and natural approaches, such as restoring wetlands and mangroves. By addressing these environmental threats, mitigation strategies aim to protect coastal communities and ecosystems from the adverse effects of changing conditions.
Nicolas Lewis: Nicolas Lewis is a notable figure known for his contributions to understanding sea level rise and its underlying causes. His work emphasizes the relationship between climate change, ocean thermal expansion, and glacial melting, which are crucial in predicting future sea level trends. By highlighting these connections, his research informs policy decisions and strategies aimed at mitigating the impacts of rising sea levels on coastal communities.
Ocean circulation: Ocean circulation refers to the continuous movement of seawater driven by various factors, including wind, temperature differences, and salinity gradients. This movement plays a crucial role in regulating climate and weather patterns, distributing heat around the globe, and influencing marine ecosystems. Understanding ocean circulation is vital for grasping the dynamics of sea level rise and its implications for coastal areas.
Saltwater Intrusion: Saltwater intrusion is the process where saltwater encroaches into freshwater aquifers, often due to over-extraction of groundwater and rising sea levels. This phenomenon is increasingly relevant as climate change contributes to both sea level rise and changes in precipitation patterns, directly affecting coastal water resources. As aquifers become contaminated with saltwater, they lose their ability to provide clean drinking water, impacting ecosystems and communities that rely on these sources.
Satellite altimetry: Satellite altimetry is a remote sensing technology that measures the distance between a satellite and the Earth's surface to determine variations in sea surface height. This technique provides critical data for monitoring sea level rise, understanding ocean dynamics, and assessing changes in regional sea levels, making it essential for various studies related to coastal resilience and climate change.
Thermal expansion: Thermal expansion is the process by which matter increases in volume as its temperature rises. This phenomenon is significant in the context of oceans, as the warming of seawater due to climate change leads to an increase in ocean volume, contributing to rising sea levels. Understanding thermal expansion is crucial for analyzing global sea level trends and regional variations, particularly how different areas may experience varying impacts from climate-induced changes in temperature.
Urbanization: Urbanization is the process through which rural areas transform into urban areas, resulting in an increase in population density and changes in land use. This phenomenon is often driven by economic opportunities, migration, and the desire for improved living standards. As urban areas expand, they can face significant challenges related to environmental issues, infrastructure demands, and cultural heritage preservation.