9.4 Sea-level changes and their impacts
5 min read•july 30, 2024
Sea-level changes shape coastlines, affecting ecosystems and human activities. From short-term tides to long-term climate shifts, various factors drive these changes, including , ice melt, and land movements.
Rising seas reshape shorelines, increase flooding, and threaten coastal communities. Impacts range from ecosystem disruption to economic losses. Adaptation strategies include engineering solutions, nature-based approaches, and to address these challenges.
Sea-level change drivers and mechanisms
Timescales and causes of sea-level changes
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- Sea-level changes occur on various timescales driven by different mechanisms
- Short-term fluctuations (hours to years) influenced by tides, , and climate patterns (El Niño-Southern Oscillation)
- Medium-term changes (decades to centuries) affected by patterns, atmospheric pressure variations, and Earth's rotation changes
- Long-term changes (millennia to millions of years) driven by plate tectonics, ocean basin volume alterations, and long-term climate cycles
- Eustatic sea-level changes represent global ocean volume changes
- Primarily caused by ice sheet melting or formation
- Thermal expansion or contraction of ocean water also contributes
- Isostatic sea-level changes result from vertical land mass movements
- Often due to glacial rebound as land rises after ice sheet removal
- Tectonic activity can cause uplift or subsidence affecting relative sea level
- Anthropogenic climate change accelerates current sea-level rise
- Increased greenhouse gas emissions lead to ocean thermal expansion
- Melting of land-based ice (glaciers, ice sheets) adds water volume to oceans
Mechanisms of sea-level change
- Thermal expansion causes sea level rise as oceans warm
- Water molecules spread out, occupying more volume
- Accounts for about 30-55% of observed sea level rise since 1971
- Melting of land ice contributes additional water to oceans
- Glaciers and ice sheets in Greenland and Antarctica are major contributors
- Mountain glaciers also play a role, though smaller in total volume
- Changes in land water storage affect sea level
- Groundwater depletion transfers water from land to oceans
- Dam construction on rivers can temporarily reduce sea level rise
- Ocean circulation changes redistribute water masses
- Alters regional sea levels through temperature and salinity differences
- Can cause sea level to rise in some areas while falling in others
- Vertical land movements affect relative sea level
- Glacial isostatic adjustment continues from the last ice age
- Tectonic plate movements cause uplift or subsidence in coastal areas
Sea-level change impacts on coastlines
Coastal geomorphology and flooding
- Sea-level changes significantly alter coastal geomorphology
- Reshape shorelines, barrier islands, and estuaries
- Modify sediment transport patterns and deposition rates
- Rising sea levels increase coastal flooding frequency and severity
- Threaten low-lying urban areas (, )
- Endanger critical infrastructure (ports, power plants)
- Inundate valuable agricultural lands in coastal plains
- affects coastal water resources
- Contaminates freshwater aquifers used for drinking water
- Impacts irrigation water quality for agriculture
- Alters salinity in estuaries and coastal wetlands
Ecosystem and economic impacts
- Coastal ecosystems face habitat loss or forced migration
- Mangroves may retreat landward or drown if sea level rise is too rapid
- Salt marshes risk submergence if sediment accretion cannot keep pace
- Coral reefs struggle with increased water depth and temperature changes
- Sea-level rise exacerbates
- Accelerates cliff instability and retreat rates
- Increases loss of beaches and dunes
- Threatens coastal properties and infrastructure
- Human activities in coastal zones face disruption
- Tourism industry affected by beach loss and flood risks
- Fisheries impacted by changes in coastal and estuarine habitats
- Port operations challenged by changing water depths and increased storm risks
- Economic consequences of sea-level changes are significant
- Property damage from increased flooding and erosion
- Loss of land value in high-risk coastal areas
- Increased costs for coastal protection measures and infrastructure adaptation
- Potential displacement of coastal communities (small island nations)
Coastal responses to sea-level rise
Erosion and inundation processes
- Coastal erosion wears away land through wave action and currents
- Removes beach sediments and undermines cliffs
- Rate influenced by wave energy, sediment supply, and coastal geology
- Inundation permanently submerges low-lying coastal areas
- Distinct from temporary flooding events
- Gradually converts terrestrial environments to marine ones
- Shoreline retreat involves landward movement of the coast
- Often quantified using the Bruun Rule for sandy beaches
- More complex models account for varying coastal types and processes
- Coastal squeeze occurs when shorelines cannot retreat landward
- Natural (cliffs) or artificial (seawalls) barriers prevent migration
- Results in loss of intertidal habitats (beaches, tidal flats)
Factors influencing coastal response
- Coastal slope affects the rate and extent of shoreline changes
- Gentle slopes experience more horizontal retreat for a given sea-level rise
- Steep slopes may see less horizontal change but increased erosion
- Sediment supply plays a crucial role in coastal response
- Surplus can help beaches keep pace with sea-level rise
- Deficits often lead to accelerated erosion and retreat
- Wave energy influences erosion rates and sediment transport
- High-energy coasts generally experience more rapid changes
- Sheltered areas may see slower but still significant impacts
- Different coastal types respond uniquely to sea-level rise
- Rocky coasts may experience cliff retreat and platform drowning
- Sandy beaches can migrate landward if space allows
- Deltas are particularly vulnerable due to subsidence and reduced sediment input
Coastal adaptation and management strategies
Engineering approaches
- Hard engineering solutions aim to protect existing coastlines
- Seawalls provide direct defense against waves and flooding
- Groins trap sediment to maintain beach width
- Potential negative impacts on coastal processes and adjacent areas
- Soft engineering approaches work with natural processes
- Beach nourishment adds sand to eroding beaches
- Dune restoration enhances natural storm buffers
- More environmentally friendly but may require frequent maintenance
- Accommodation strategies modify existing structures and land uses
- Elevating buildings on stilts in flood-prone areas
- Implementing flood-resistant designs for new construction
- Creating water retention areas to manage increased runoff
Nature-based and policy solutions
- Nature-based solutions combine ecological restoration with protection
- Living shorelines use native vegetation to stabilize coasts
- Artificial reefs reduce wave energy while providing habitat
- Mangrove and salt marsh restoration enhances natural buffers
- Managed retreat involves planned relocation from high-risk areas
- Gradual movement of people and assets to safer ground
- Can include buy-out programs for vulnerable properties
- Allows coastal ecosystems to migrate naturally
- Integrated coastal zone management (ICZM) balances multiple objectives
- Coordinates environmental, economic, and social goals
- Involves stakeholders in decision-making processes
- Considers long-term sustainability of coastal resources
- Adaptive management approaches allow flexibility in strategies
- Regular reassessment of sea-level rise projections and impacts
- Adjusting plans as new information becomes available
- Implementing phased approaches to coastal protection and retreat
Key Terms to Review (18)
Altimetry: Altimetry is the measurement of altitude or elevation, typically using a device called an altimeter. In the context of sea-level changes, altimetry plays a crucial role in monitoring variations in sea level caused by factors like climate change, melting ice caps, and ocean currents. By utilizing satellite technology, altimetry provides critical data that helps scientists understand how sea-level fluctuations can impact coastal communities and ecosystems.
Coastal Defense: Coastal defense refers to the strategies and structures implemented to protect coastlines from erosion, flooding, and other impacts of sea-level rise and extreme weather events. These measures aim to safeguard human life, property, and ecosystems along the coast, often involving a combination of natural and engineered solutions. Effective coastal defense is crucial in response to the challenges posed by sea-level changes, ensuring resilience against environmental threats.
Coastal Erosion: Coastal erosion is the process by which shorelines are gradually worn away due to the action of waves, currents, tides, and human activities. This dynamic process plays a significant role in shaping coastal landscapes, impacting ecosystems, and influencing human settlement patterns along coastlines.
Delta formation: Delta formation is the process by which sediment carried by a river is deposited as the river meets a standing body of water, creating a landform that typically has a triangular or fan shape. This process results from the interaction between flowing water and stagnant water, leading to the accumulation of sediments over time, which can create rich habitats and influence local ecosystems.
Eustatic sea-level change: Eustatic sea-level change refers to the global rise or fall of sea levels due to changes in the volume of water in the world's oceans or alterations in the shape of ocean basins. This phenomenon is primarily influenced by factors such as glacial melting, thermal expansion of water as it warms, and tectonic movements. Understanding eustatic changes is essential for grasping their significant impacts on coastal environments, ecosystems, and human activities.
Flood risk: Flood risk refers to the likelihood of flooding occurring in a specific area, along with the potential consequences of such an event. This concept involves understanding how rising sea levels can exacerbate flooding, particularly in coastal and low-lying regions, leading to significant impacts on communities, ecosystems, and infrastructure. Assessing flood risk is crucial for planning, mitigation, and adaptation strategies in the face of changing environmental conditions.
Glacial melting: Glacial melting refers to the process by which glaciers and ice sheets lose mass as they melt due to rising temperatures, primarily driven by climate change. This melting contributes significantly to sea-level rise, as the water from melted glaciers flows into oceans and seas, impacting coastal ecosystems and human communities.
Holocene Transgression: Holocene transgression refers to the rising sea levels that occurred during the Holocene epoch, starting around 11,700 years ago and continuing to the present. This phenomenon has significant implications for coastal environments, leading to the inundation of land and the alteration of habitats as sea levels rise due to melting ice caps and thermal expansion of seawater.
Isostatic Rebound: Isostatic rebound refers to the process where the Earth's crust rises after being compressed by the weight of ice sheets or other heavy loads. This adjustment occurs after the melting of ice or the removal of weight, allowing the crust to gradually regain its equilibrium. This phenomenon is crucial in understanding landscape changes and geological processes following glaciations, erosion, and shifts in sea levels.
Last glacial maximum: The last glacial maximum (LGM) refers to the most recent period during the last Ice Age when ice sheets were at their greatest extent, occurring around 26,500 years ago. This event significantly influenced global climate patterns, sea levels, and landscapes, leaving lasting impacts on the Earth’s surface processes and environments that are still observable today.
Managed retreat: Managed retreat is a strategic response to the impacts of sea-level rise, where communities voluntarily relocate or abandon properties and infrastructure in vulnerable coastal areas. This approach aims to reduce risk and enhance resilience by moving people and assets away from high-risk zones while allowing natural processes to occur. It involves careful planning, community engagement, and often governmental support to ensure a smooth transition for affected residents.
Miami: Miami is a major coastal city located in the southeastern region of Florida, known for its diverse culture, vibrant nightlife, and significant economic contributions. Its geographical location makes it particularly vulnerable to sea-level changes, which can lead to increased flooding, erosion, and changes in local ecosystems, impacting both urban development and natural habitats.
Ocean circulation: Ocean circulation refers to the large-scale movement of water in the world's oceans, driven by various forces such as wind, temperature, salinity differences, and the Earth's rotation. This movement plays a critical role in regulating climate, distributing heat, and influencing sea-level changes. The patterns of ocean circulation also impact marine ecosystems and weather systems across the globe.
Saltwater intrusion: Saltwater intrusion is the process where seawater encroaches into freshwater aquifers, typically caused by a combination of over-extraction of groundwater and rising sea levels. This phenomenon affects coastal regions, leading to the contamination of drinking water sources and impacting agricultural practices due to increased salinity in soils. Understanding saltwater intrusion is crucial in assessing the implications of sea-level rise and freshwater resource management.
Storm surges: Storm surges are temporary rises in sea level caused by strong winds and low atmospheric pressure associated with storms, particularly hurricanes and tropical storms. These surges can lead to significant coastal flooding, especially when they coincide with high tide, making them a critical factor in understanding sea-level changes and their impacts on coastal regions.
Thermal Expansion: Thermal expansion is the tendency of matter to change in volume in response to a change in temperature. As temperatures rise, materials expand, and this can significantly impact various geological and environmental processes, influencing physical weathering, sea levels, and the dynamics of climate change. Understanding thermal expansion is essential for grasping how these processes interact with each other and shape the Earth's surface over time.
Tide gauge: A tide gauge is an instrument used to measure the change in water levels, specifically tidal fluctuations, in oceans, seas, and other bodies of water. It helps to monitor the rise and fall of tides, which are influenced by gravitational forces, and provides critical data for understanding coastal processes and sea-level changes over time.
Venice: Venice is a city in northeastern Italy known for its unique canal system and rich history as a major maritime power. The city faces significant challenges due to sea-level rise, making it a prime example of how coastal urban areas are impacted by environmental changes.