Significant challenges to the sustainability of the California coast considering climate change.

Climate change is an existential threat to the environmental and socioeconomic sustainability of the coastal zone and impacts will be complex and widespread. Evidence from California and across the United States shows that climate change is impacting coastal communities and challenging managers with a plethora of stressors already present. Widespread action could be taken that would sustain California's coastal ecosystems and communities. In this perspective, we highlight the main threat to coastal sustainability: the compound effects of episodic events amplified with ongoing climate change, which will present unprecedented challenges to the state. We present two key challenges for California's sustainability in the coastal zone: 1) accelerating sea-level rise combined with storm impacts, and 2) continued warming of the oceans and marine heatwaves. Cascading effects from these types of compounding events will occur within the context of an already stressed system that has experienced extensive alterations due to intensive development, resource extraction and harvesting, spatial containment, and other human use pressures. There are critical components that could be used to address these immediate concerns, including comanagement strategies that include diverse groups and organizations, strategic planning integrated across large areas, rapid implementation of solutions, and a cohesive and policy relevant research agenda for the California coast. Much of this has been started in the state, but the scale could be increased, and timelines accelerated. The ideas and information presented here are intended to help expand discussions to sharpen the focus on how to encourage sustainability of California's iconic coastal region.

Widespread seawater intrusions beneath the grounded ice of Thwaites Glacier, West Antarctica.

Warm water from the Southern Ocean has a dominant impact on the evolution of Antarctic glaciers and in turn on their contribution to sea level rise. Using a continuous time series of daily-repeat satellite synthetic-aperture radar interferometry data from the ICEYE constellation collected in March-June 2023, we document an ice grounding zone, or region of tidally controlled migration of the transition boundary between grounded ice and ice afloat in the ocean, at the main trunk of Thwaites Glacier, West Antarctica, a strong contributor to sea level rise with an ice volume equivalent to a 0.6-m global sea level rise. The ice grounding zone is 6 km wide in the central part of Thwaites with shallow bed slopes, and 2 km wide along its flanks with steep basal slopes. We additionally detect irregular seawater intrusions, 5 to 10 cm in thickness, extending another 6 km upstream, at high tide, in a bed depression located beyond a bedrock ridge that impedes the glacier retreat. Seawater intrusions align well with regions predicted by the GlaDS subglacial water model to host a high-pressure distributed subglacial hydrology system in between lower-pressure subglacial channels. Pressurized seawater intrusions will induce vigorous melt of grounded ice over kilometers, making the glacier more vulnerable to ocean warming, and increasing the projections of ice mass loss. Kilometer-wide, widespread seawater intrusion beneath grounded ice may be the missing link between the rapid, past, and present changes in ice sheet mass and the slower changes replicated by ice sheet models.

Climate migration amplifies demographic change and population aging.

The warnings of potential climate migration first appeared in the scientific literature in the late 1970s when increased recognition that disintegrating ice sheets could drive people to migrate from coastal cities. Since that time, scientists have modeled potential climate migration without integrating other population processes, potentially obscuring the demographic amplification of this migration. Climate migration could amplify demographic change-enhancing migration to destinations and suppressing migration to origins. Additionally, older populations are the least likely to migrate, and climate migration could accelerate population aging in origin areas. Here, we investigate climate migration under sea-level rise (SLR), a single climatic hazard, and examine both the potential demographic amplification effect and population aging by combining matrix population models, flood hazard models, and a migration model built on 40 y of environmental migration in the United States to project the US population distribution of US counties. We find that the demographic amplification of SLR for all feasible Representative Concentration Pathway-Shared Socioeconomic Pathway (RCP-SSP) scenarios in 2100 ranges between 8.6-28 M [5.7-53 M]-5.3 and 18 times the number of migrants (0.4-10 M). We also project significant aging of coastal areas as youthful populations migrate but older populations remain, accelerating population aging in origin areas. As the percentage of the population lost due to climate migration increases, the median age also increases-up to 10+ y older in some highly impacted coastal counties. Additionally, our population projection approach can be easily adapted to investigate additional or multiple climate hazards.

Poyang and Dongting Lakes, Yangtze River: tributary lakes blocked by main-stem aggradation.

During its 6,300-km course from the Tibetan Plateau to the ocean, the Yangtze River is joined by two large lakes: Dongting Lake and Poyang Lake. We explain why these lakes exist. Deglaciation forced the ocean adjacent to the Yangtze mouth to rise ∼120 m. This forced a wave of rising water surface elevation and concomitant bed aggradation upstream. While aggradation attenuated upstream, the low bed slope of the Middle-Lower Yangtze River (∼2 × 10-5 near Wuhan) made it susceptible to sea level rise. The main stem, sourced at 5,054 m above sea level, had a substantial sediment load to "fight" against water surface level rise by means of bed aggradation. The tributaries of the Middle-Lower Yangtze have reliefs of approximately hundreds of meters, and did not have enough sediment supply to fill the tributary accommodation space created by main-stem aggradation. We show that the resulting tributary blockage likely gave rise to the lakes. We justify this using field data and numerical modeling, and derive a dimensionless number capturing the critical rate of water surface rise for blockage versus nonblockage.

More extensive land loss expected on coastal deltas due to rivers jumping course during sea-level rise.

River deltas are home to hundreds of millions of people worldwide and are in danger of sinking due to anthropogenic sea-level rise, land subsidence, and reduced sediment supply. Land loss is commonly forecast by averaging river sediment supply across the entire delta plain to assess whether deposition can keep pace with sea-level rise. However, land loss and deposition vary across the landscape because rivers periodically jump course, rerouting sediment to distinct subregions called delta lobes. Here, we developed a model to forecast land loss that resolves delta lobes and tested the model against a scaled laboratory experiment. Both the model and the experiment show that rivers build land on the active lobe, but the delta incurs gradual land loss on inactive lobes that are cut off from sediment after the river abandons course. The result is a band of terrain along the coast that is usually drowned but is nonetheless a sink for sediment when the lobe is active, leaving less of the total sediment supply available to maintain persistent dry land. Land loss is expected to be more extensive than predicted by classical delta-plain-averaged models. Estimates for eight large deltas worldwide suggest that roughly half of the riverine sediment supply is delivered to terrain that undergoes long periods of submergence. These results draw the sustainability of deltas further into question and provide a framework to plan engineered diversions at a pace that will mitigate land loss in the face of rising sea levels.

Rising plant demand strengthens nitrogen limitation in tidal marsh.

Nitrogen (N) is a limiting nutrient for primary productivity in most terrestrial ecosystems, but whether N limitation is strengthening or weakening remains controversial because both N sources and sinks are increasing in magnitude globally. Temperate marshes are exposed to greater amounts of external N inputs than most terrestrial ecosystems and more than in preindustrial times owing to their position downstream of major sources of human-derived N runoff along river mouths and estuaries. Simultaneously, ecosystem N demand may also be increasing owing to other global changes such as rising atmospheric [CO2]. Here, we used interannual variability in external drivers and variables related to exogenous supply of N, along with detailed assessments of plant growth and porewater biogeochemistry, to assess the severity of N-limitation, and to determine its causes, in a 14-year N-addition × elevated CO2 experiment. We found substantial interannual variability in porewater [N], plant growth, and experimental N effects on plant growth, but the magnitude of N pools through time varied independently of the strength of N limitation. Sea level, and secondarily salinity, related closely to interannual variability in growth of the dominant plant functional groups which drove patterns in N limitation and in porewater [N]. Experimental exposure of plants to elevated CO2 and years with high flooding strengthened N limitation for the sedge. Abiotic variables controlled plant growth, which determined the strength of N limitation for each plant species and for ecosystem productivity as a whole. We conclude that in this ecosystem, which has an open N cycle and where N inputs are likely greater than in preindustrial times, plant N demand has increased more than supply.

The Coastal Carbon Library and Atlas: Open source soil data and tools supporting blue carbon research and policy.

Quantifying carbon fluxes into and out of coastal soils is critical to meeting greenhouse gas reduction and coastal resiliency goals. Numerous 'blue carbon' studies have generated, or benefitted from, synthetic datasets. However, the community those efforts inspired does not have a centralized, standardized database of disaggregated data used to estimate carbon stocks and fluxes. In this paper, we describe a data structure designed to standardize data reporting, maximize reuse, and maintain a chain of credit from synthesis to original source. We introduce version 1.0.0. of the Coastal Carbon Library, a global database of 6723 soil profiles representing blue carbon-storing systems including marshes, mangroves, tidal freshwater forests, and seagrasses. We also present the Coastal Carbon Atlas, an R-shiny application that can be used to visualize, query, and download portions of the Coastal Carbon Library. The majority (4815) of entries in the database can be used for carbon stock assessments without the need for interpolating missing soil variables, 533 are available for estimating carbon burial rate, and 326 are useful for fitting dynamic soil formation models. Organic matter density significantly varied by habitat with tidal freshwater forests having the highest density, and seagrasses having the lowest. Future work could involve expansion of the synthesis to include more deep stock assessments, increasing the representation of data outside of the U.S., and increasing the amount of data available for mangroves and seagrasses, especially carbon burial rate data. We present proposed best practices for blue carbon data including an emphasis on disaggregation, data publication, dataset documentation, and use of standardized vocabulary and templates whenever appropriate. To conclude, the Coastal Carbon Library and Atlas serve as a general example of a grassroots F.A.I.R. (Findable, Accessible, Interoperable, and Reusable) data effort demonstrating how data producers can coordinate to develop tools relevant to policy and decision-making.

Upland forest retreat lags behind sea-level rise in the mid-Atlantic coast.

Ghost forests consisting of dead trees adjacent to marshes are striking indicators of climate change, and marsh migration into retreating coastal forests is a primary mechanism for marsh survival in the face of global sea-level rise. Models of coastal transgression typically assume inundation of a static topography and instantaneous conversion of forest to marsh with rising seas. In contrast, here we use four decades of satellite observations to show that many low-elevation forests along the US mid-Atlantic coast have survived despite undergoing relative sea-level rise rates (RSLRR) that are among the fastest on Earth. Lateral forest retreat rates were strongly mediated by topography and seawater salinity, but not directly explained by spatial variability in RSLRR, climate, or disturbance. The elevation of coastal tree lines shifted upslope at rates correlated with, but far less than, contemporary RSLRR. Together, these findings suggest a multi-decadal lag between RSLRR and land conversion that implies coastal ecosystem resistance. Predictions based on instantaneous conversion of uplands to wetlands may therefore overestimate future land conversion in ways that challenge the timing of greenhouse gas fluxes and marsh creation, but also imply that the full effects of historical sea-level rise have yet to be realized.

Sunny-Day Flooding and Mortality Risk in Coastal Florida.

Sea-level rise is likely to worsen the impacts of hurricanes, storm surges, and tidal flooding on coastal access to basic services. We investigate the historical impact of tidal flooding on mortality rates of the elderly population in coastal Florida using administrative records of individual deaths, demographics, and residential location combined with tidal gauge and high-resolution elevation data. We incorporate data capturing storm and precipitation events into our empirical model to distinguish between disruptions from routine sunny-day flooding and less predictable tropical storm-induced flooding. We find that a 1-standard-deviation (20-millimeter) increase in tidal flooding depth increases mortality rates by 0.46% to 0.60% among those aged 65 or older. Our estimates suggest that future sea-level rises may contribute to an additional 130 elderly deaths per year in Florida relative to 2019, all else being equal. The enhanced risk is concentrated among residents living more than nine minutes away from the nearest hospital. Results suggest that tidal flooding may augment elderly mortality risk by delaying urgent medical care.

Economic evaluation of sea-level rise adaptation strongly influenced by hydrodynamic feedbacks.

Coastal communities rely on levees and seawalls as critical protection against sea-level rise; in the United States alone, $300 billion in shoreline armoring costs are forecast by 2100. However, despite the local flood risk reduction benefits, these structures can exacerbate flooding and associated damages along other parts of the shoreline-particularly in coastal bays and estuaries, where nearly 500 million people globally are at risk from sea-level rise. The magnitude and spatial distribution of the economic impact of this dynamic, however, are poorly understood. Here we combine hydrodynamic and economic models to assess the extent of both local and regional flooding and damages expected from a range of shoreline protection and sea-level rise scenarios in San Francisco Bay, California. We find that protection of individual shoreline segments (5 to 75 km) can increase flooding in other areas by as much as 36 million m3 and damages by $723 million for a single flood event and in some cases can even cause regional flood damages that exceed the local damages prevented from protection. We also demonstrate that strategic flooding of certain shoreline segments, such as those with gradually sloping baylands and space for water storage, can help alleviate flooding and damages along other stretches of the coastline. By matching the scale of the economic assessment to the scale of the threat, we reveal the previously uncounted costs associated with uncoordinated adaptation actions and demonstrate that a regional planning perspective is essential for reducing shared risk and wisely spending adaptation resources in coastal bays.

This land is your land, this could be marsh land: Property parcel characteristics of marsh migration corridors in Rhode Island, USA.

Salt marshes, critical habitats offering many ecosystem services, are threatened by development, accelerated sea level rise (SLR) and other anthropogenic stressors that are projected to worsen. As seas rise, some salt marshes can migrate inland if there is adjacent, permeable, undeveloped land available. Facilitating marsh migration is necessary for coastal resilience efforts, but extensive coastal development can make finding suitable migration corridors challenging. This work seeks to characterize changes in land use, ownership, and economic value at the property parcel level within current versus future marsh areas for the state of Rhode Island, USA. We find that most parcels currently containing salt marsh are publicly owned, whereas most adjacent parcels projected to contain new salt marsh in 2050 are privately owned. Additionally, parcels containing new marsh in 2050 have 47% higher per-hectare assessed values than parcels containing current marsh. We describe the locations and characteristics of parcels within migration corridors with the lowest per-hectare values that may be the most cost-effective for marsh conservation practitioners to protect. This study highlights the expanding land use types and landowner sets that will be involved in marsh conservation decisions, and the economic value of potential migration corridors where costly tradeoffs may be necessary to promote coastal resilience.

Modeling the impact of sea level rise on endangered deer habitat.

Numerous unique flora and fauna inhabit the Lower Florida Keys, including the endangered Florida Key deer, found nowhere else. In this vulnerable habitat of flat islands with low elevation, accelerated sea level rise poses a threat. Predicting the impact of sea level rise on vegetation and wildlife is crucial. This study used 5 Intergovernmental Panel on Climate Change (IPCC) sea level rise scenarios to assess their effects on No Name Key, Florida. The goal was to estimate changes in the Florida Key deer population relative to sea level rise using a lidar-derived elevation data and a vegetation map. The method used 2 cases to model the sea level rise impact. In Case 1, total non-submerged area at current sea level was determined. Using 5 IPCC scenarios, a new total non-submerged land area was estimated, and deer numbers were predicted for each scenario. In Case 2, upward migration of coastal vegetation combined with the coastal squeeze process was modeled. A distinct elevation range for each vegetation type at the current sea level was determined. Vegetation ranges were redistributed based on respective elevation ranges in the sea level rise scenarios. Areas for each vegetation type were recalculated, and Key deer numbers were estimated for each sea level rise scenario. Results under the worst emission scenario showed the following: (1) for case 1, the land area was reduced to 30 % of the current land area, corresponding to having about 27 deer, and (2) for case 2, the land area was reduced to 70 % of the current land area, having about 54 deer on No Name Key. The results indicated reduced non-submerged land area and less upland vegetation, particularly hardwoods/hammocks, by the year 2100. As less land area is available, a decline in Key deer population is expected as sea levels rise. Since Key deer favor upland vegetation, habitat affected by sea level rise will likely support a smaller deer population. The findings emphasize the need for precise, timely predictions of sea level rise impacts and long-term conservation strategies. Specifically designed measures are required to protect and maintain endangered wildlife, such as the Florida Key deer, residing on these vulnerable islands.

Increasing Salt Marsh Elevation Using Sediment Augmentation: Critical Insights from Surface Sediments and Sediment Cores.

Sea-level rise is particularly concerning for tidal wetlands that reside within an area with steep topography or are constrained by human development and alteration of sedimentation. Sediment augmentation to increase wetland elevations has been considered as a potential strategy for such areas to prevent wetland loss over the coming decades. However, there is little information on the best approaches and whether adaptive management actions can mimic natural processes to build sea-level rise resilience. In addition, the lack of information on long-term marsh characteristics, processes, and variability can hamper development of effective augmentation strategies. Here, we assess a case study in a southern California marsh to determine the nature of the pre-existing sediments and variability of the site in relation to sediments applied during an augmentation experiment. Although sediment cores revealed natural variations in the grain size and organic content of sediments deposited at the site over the past 1500 years, the applied sediments were markedly coarser in grain size than prehistoric sediments at the site (100% maximum sand versus 76% maximum sand). The rate of the experimental sediment application (25.1 ± 1.09 cm in ~2 months) was also much more rapid than natural accretion rates measured for the site historically. In contrast, post-augmentation sediment accretion rates on the augmentation site have been markedly slower than pre-augmentation rates or current rates on a nearby control site. The mismatch between the characteristics of the applied sediment and thickness of application and the historic conditions are likely strong contributors to the slow initial recovery of vegetation. Sediment augmentation has been shown to be a useful strategy in some marshes, but this case study illustrates that vegetation recovery may be slow if applied sediments are not similar or at a thickness similar to historic conditions. However, testing adaptation strategies to build wetland elevations is important given the long-term risk of habitat loss with sea-level rise. Lessons learned in the case study could be applied elsewhere.

Risk assessment of national railway infrastructure due to sea-level rise: an application of a methodological framework in Italian coastal railways.

Nowadays, within the built environment, railway infrastructures play a key role to sustain national policies oriented toward promoting sustainable mobility. For this reason, national institutions and infrastructure managers need to increase their awareness in relation to the current and future climate risks on their representative systems. Among climate change impacts, preventing the effects of sea-level rise (SLR) on coastal railway infrastructures is a priority. The first step in the climate change adaptation policy cycle is the development of an ad hoc climate risk assessment. In this view, this research develops a vulnerability and a risk assessment metric to identify the hotspots within a national coastal railway due to the SLR impacts. The proposed methodology required different steps to quantify the SLR projections and the vulnerability characteristics of the assets, in terms of sensitivity and adaptive capacity. The investigated case study is the coastal railway infrastructure in Italy, thanks to an initial approach of co-design participative processes with the national Infrastructure Manager: Rete Ferroviaria Italiana (RFI). The results of this application, although not included in the paper due to confidential reasons imposed by the infrastructure manager - led to a clear identification of the areas and the coastal railway sections which are exposed to high levels of risks and of the places which require priority actions for urgent adaptation in a view of climate proof infrastructures.

Three Reconstructions of 'Effectiveness': Some Implications for State Continuity and Sea-level Rise.

Small Island Developing States (SIDS) are uniquely threatened by rising sea levels. Not only does the retreat of their coastlines place them in danger of losing maritime territory; the concurrent possibility of their landmasses becoming either uninhabitable or completely submerged also threatens their very existence. According to one understanding of the law that governs the continuity and extinction of states, political communities that permanently lose 'effectiveness'-typically understood as sufficient governmental control of a relatively determinate territory with a permanent population-must lose their statehood as well. In this article, I provide three reconstructions of effectiveness, each of which rests upon a different normative rationale. My contention is that, regardless of which reconstruction one adopts, the continuity of submerged SIDS is eminently supportable, notwithstanding the arguments frequently made in favour of their formal extinction.

Measuring glacier mass changes from space-a review.

Glaciers distinct from the Greenland and Antarctic ice sheets are currently losing mass rapidly with direct and severe impacts on the habitability of some regions on Earth as glacier meltwater contributes to sea-level rise and alters regional water resources in arid regions. In this review, we present the different techniques developed during the last two decades to measure glacier mass change from space: digital elevation model (DEM) differencing from stereo-imagery and synthetic aperture radar interferometry, laser and radar altimetry and space gravimetry. We illustrate their respective strengths and weaknesses to survey the mass change of a large Arctic ice body, the Vatnajökull Ice Cap (Iceland) and for the steep glaciers of the Everest area (Himalaya). For entire regions, mass change estimates sometimes disagree when a similar technique is applied by different research groups. At global scale, these discrepancies result in mass change estimates varying by 20%-30%. Our review confirms the need for more thorough inter-comparison studies to understand the origin of these differences and to better constrain regional to global glacier mass changes and, ultimately, past and future glacier contribution to sea-level rise.

Mangrove expansion on the low wooded islands of the Great Barrier Reef.

Mangrove forests are the dominant vegetation growing on low wooded islands, which occur in the Caribbean, Indian and Pacific Oceans. In the northern Great Barrier Reef, we map remarkable, undocumented mangrove forest extension on 10 low wooded islands in the Howick Group that collectively equates to an area of 667 000 m2 (66.7 ha). We combine extensive field survey with canopy height models derived from RPA imagery and allometric scaling to quantify above ground biomass in both old (pre-1973) and new (post-1973) forest areas. Forest expansion added approximately 10 233 tonnes of new biomass since the early 1970s. We suggest that such substantial expansion of mangrove forest has occurred within a short time span in response to changing environmental controls. These may include sea-level rise, sediment transport and deposition, cyclone impact and the development of associated reef flat sedimentary landforms including unconsolidated and lithified shingle ridges, which influence reef flat hydrodynamics. Our observations highlight the globally dynamic response of mangrove distribution and forest structure to environmental change and provide timely new estimates from understudied reef island settings.

Complex eco-evolutionary responses of a foundational coastal marsh plant to global change.

Predicting the fate of coastal marshes requires understanding how plants respond to rapid environmental change. Environmental change can elicit shifts in trait variation attributable to phenotypic plasticity and act as selective agents to shift trait means, resulting in rapid evolution. Comparably, less is known about the potential for responses to reflect the evolution of trait plasticity. Here, we assessed the relative magnitude of eco-evolutionary responses to interacting global change factors using a multifactorial experiment. We exposed replicates of 32 Schoenoplectus americanus genotypes 'resurrected' from century-long, soil-stored seed banks to ambient or elevated CO2 , varying levels of inundation, and the presence of a competing marsh grass, across two sites with different salinities. Comparisons of responses to global change factors among age cohorts and across provenances indicated that plasticity has evolved in five of the seven traits measured. Accounting for evolutionary factors (i.e. evolution and sources of heritable variation) in statistical models explained an additional 9-31% of trait variation. Our findings indicate that evolutionary factors mediate ecological responses to environmental change. The magnitude of evolutionary change in plant traits over the last century suggests that evolution could play a role in pacing future ecosystem response to environmental change.

Tropical estuarine ecosystem change under the interacting influences of future climate and ecosystem restoration.

One of the largest restoration programs in the world, the Comprehensive Everglades Restoration Plan (CERP) aims to restore freshwater inputs to Everglades wetlands and the Florida Bay estuary. This study predicted how the Florida Bay ecosystem may respond to hydrological restoration from CERP within the context of contemporary projected impacts of sea-level rise (SLR) and increased future temperatures. A spatial-temporal dynamic model (Ecospace) was used to develop a spatiotemporal food web model incorporating environmental drivers of salinity, salinity variation, temperature, depth, distance to mangrove, and seagrass abundance and was used to predict responses of biomass, fisheries catch, and ecosystem resilience between current and future conditions. Changes in biomass between the current and future scenario suggest a suite of winners and losers, with many estuarine species increasing in both total biomass and spatial distribution. Notable biomass increases were predicted for important forage species, including bay anchovy (+32%), hardhead halfbeak (+19%), and pinfish (+31%), while decreases were predicted in mullet (-88%), clupeids (-55%), hardhead silverside (-15%), mojarras (-117%), and Portunid crabs (-16%). Increases in sportfish biomass included the angler-preferred spotted seatrout (+9%), red drum (+10%), and gray snapper (+8%), while decreases included sheepshead (-40%), Atlantic tarpon (-73%), and common snook (-507%). Ecosystem resilience and fisheries catch of angler-preferred species were predicted to improve in the future scenario in total, although a localized decline in resilience predicted for the Central Region may warrant further attention. Our results suggest the Florida Bay ecosystem is likely to achieve restoration benefits in spite of, and in some cases facilitated by, the projected future impacts from climate change due to the system's shallow depth and detrital dominance. The incorporation of climate impacts into long-term restoration planning using ecosystem modeling in similar systems facing unknown futures of SLR, warming seas, and shifting species distributions is recommended.

Climate change mitigation potential of Louisiana's coastal area: Current estimates and future projections.

Coastal habitats can play an important role in climate change mitigation. As Louisiana implements its climate action plan and the restoration and risk-reduction projects outlined in its 2017 Louisiana Coastal Master Plan, it is critical to consider potential greenhouse gas (GHG) fluxes in coastal habitats. This study estimated the potential climate mitigation role of existing, converted, and restored coastal habitats for years 2005, 2020, 2025, 2030, and 2050, which align with the Governor of Louisiana's GHG reduction targets. An analytical framework was developed that considered (1) available scientific data on net ecosystem carbon balance fluxes per habitat and (2) habitat areas projected from modeling efforts used for the 2017 Louisiana Coastal Master Plan to estimate the net GHG flux of coastal area. The coastal area was estimated as net GHG sinks of -38.4 ± 10.6 and -43.2 ± 12.0 Tg CO2 equivalents (CO2 e) in 2005 and 2020, respectively. The coastal area was projected to remain a net GHG sink in 2025 and 2030, both with and without the implementation of Coastal Master Plan projects (means ranged from -25.3 to -34.2 Tg CO2 e). By 2050, with model-projected wetland loss and conversion of coastal habitats to open water due to coastal erosion and relative sea level rise, Louisiana's coastal area was projected to become a net source of GHG emissions both with and without the Coastal Master Plan projects. However, in the year 2050, the Louisiana Coastal Master Plan project implementation was projected to avoid the release of +8.8 ± 1.3 Tg CO2 e compared with an alternative with no action. Reduction in current and future stressors to coastal habitats, including impacts from sea level rise, as well as the implementation of restoration projects could help to ensure coastal areas remain a natural climate solution.