Sawgrasses and lilies in the Everglades.
Technical Summary

Coastal Wetland Protection

Project Drawdown defines coastal wetland protection as: the legal protection of carbon-rich mangroves, seagrasses, and saltmarshes, leading to reduced degradation rates and the safeguarding of carbon sinks. This solution secures otherwise vulnerable coastal wetlands whose destruction would be a source of greenhouse gasses.

Coastal wetlands significantly impact global carbon cycles and their disturbance contributes to an estimated 1-10% of anthropogenic carbon emissions. Unlike most terrestrial ecosystems, coastal wetlands can continue sequestering carbon for centuries without becoming saturated. As a result, they have accumulated vast stores of carbon, making their global significance high despite their small area. Yet, these ecosystems are being degraded rapidly due to human activity, and relatively few are protected.

Coastal wetlands also provide important ecosystem services. These ecosystems are being replaced for other uses, including coastal development and agriculture, releasing their stored carbon and preventing future sequestration. The coastal wetland protection solution proposes increased protection of these important carbon reservoirs, with mitigation impact via emissions reduction and biosequestration.

The oceans are the world's largest carbon sink, yet their climate mitigation potential has received little attention. Coastal wetland protection is one component of a "blue carbon" strategy, which also includes restoration of coastal wetlands and the Coming Attractions marine permaculture and ocean farming.

Methodology

Total Land Area[1]

The total global area of coastal wetlands is 53.2 million hectares, of which 12.6 million hectares are already protected.[2] The modeling of the coastal wetlands was based on the individual modeling of mangroves, seagrasses, and salt marshes. The total land area available for this solution was modeled using the annual rate of degradation for mangroves, seagrasses, and salt marshes, i.e. 0.99 percent, 2.18 percent, and 1.50 percent, respectively. Thus, an estimation was made for future degraded and non-degraded mangroves, seagrasses, and salt marshes, and the non-degraded area (which is not yet protected) was considered the available area for protection as part of this solution.

Adoption Scenarios[3]

Eight custom adoption scenarios were developed for each of these three coastal wetlands using a linear growth curve. Given the small area of coastal wetlands, the high urgency because of the annual degradation of unprotected coastal wetlands, and the high mitigation efficiency of protection, several scenarios emphasized early peak adoption by 2030.

Impacts of increased adoption of coastal wetland protection from 2020-2050 were generated based on two growth scenarios, which were assessed in comparison to a Reference Scenario where the solution’s market share was fixed at the current levels.

  • Scenario 1: This scenario results in the protection of 30.02million hectares of unprotected coastal wetlands.
  • Scenario 2: Adoption is intensified under this scenario based on the most aggressive adoption scenarios, and results in the protection of 34.69 million hectares of unprotected coastal wetlands.

Achieving 100 percent protection of unprotected coastal wetlands, even under the most aggressive adoption scenarios, was assumed to be unachievable due to the continuous annual degradation of coastal wetlands.

Emissions, Sequestration, and Yield Model

Emissions from degraded or deforested mangroves are set at 32.75 tons of carbon dioxide-equivalent per hectare per year, based on meta-analysis of 19 data points from 11 sources. Mangrove carbon storage is set to 585.77 tons of carbon per hectare based on 9 data points from 4 sources. Salt marsh sequestration rates are 1.92 tons of carbon per hectare per year, based on 27 data points from 11 sources. Emissions from degraded salt marshes are 14.29 tons of carbon dioxide-equivalent per hectare per year, based on 8 data points from 5 sources. Salt marsh carbon storage is estimated at 355.07 tons of carbon per hectare based on 4 data points from 4 sources.  Seagrass sequestration is set at 1.19 tons of carbon per hectare per year, based on 2 data points from 1 source which is a meta-analysis of 155 different sites (Duarte et al., 2010). Emissions from degraded seagrass beds are set at 3.81 tons of carbon dioxide-equivalent per hectare per year, based on 10 data points from 7 sources. Seagrass carbon storage is estimated at 234.60 tons of carbon per hectare based on 2 data points from 1 source, which is a meta-analysis of 3,640 observations at 946 different locations globally (Fourqurean et al., 2012).Financial Model

Financials are not modeled, as costs are not necessarily carried out by the landowner or land manager.

Integration[4]

The coastal wetland protection solution was not affected by integration with other solutions, as coastal wetlands are largely distinct from terrestrial land uses. An exception is mangroves, which were included in the “forest” land use model but were given highest priority, and were therefore not limited by any other forest land use.

Results

Total adoption in the Scenario 1 is 30.02 million hectares in 2050, representing 56.4 percent of the total available land. Of this, 17.6 million hectares are adopted from 2020-2050. The emissions impact of this scenario is 0.99 gigatons of carbon dioxide-equivalent reduced by 2050. Total carbon protected is 38.9 gigatons of carbon dioxide-equivalent. Financial impacts are not modeled.

Total adoption in the Scenario 2 is 34.69 million hectares in 2050, representing 65.2 percent of the total available land. Of this, 22.09 million hectares are adopted from 2020-2050. The impact of this scenario is 1.45 gigatons of carbon dioxide-equivalent by 2050. Total carbon protected is 44.4 gigatons of carbon dioxide-equivalent.

Discussion

The International Union for the Conservation of Nature and The Nature Conservancy report that if costal wetland destruction was halved, it would result in an annual emissions reduction of 0.23 gigatons of carbon dioxide per hectare per year (Herr and Landis, 2016). Griscom et al (2017)’s “Natural climate solutions” calculate 0.18-0.30 gigatons of carbon dioxide equivalent per year in 2030. The Drawdown coastal wetland protection and coastal wetland restoration model shows a maximum annual reduction of 0.03-0.06, gigatons in 2030. The lower impact could be attributed to the lower degradation rate in the drawdown models, where multiple sources citing the same degradation rate are excluded from the analysis in order to avoid double counting.

Net costs and savings should be calculated for future upgrades of this solution. More data on salt marsh and seagrass sequestration and emissions rates are also needed. It would be also useful to model restoration in addition to protection.

Like peatlands, coastal wetlands harbor a disproportionate share of the world's stored carbon. They also provide critical ecosystem services. Thus, aggressive efforts to protect these ecosystems are an important component of climate change mitigation efforts.

 

[1] To learn more about the Total Land Area for the Land Use Sector, click the Sector Summary: Land Use link below.

[2] Based on meta-analysis of protection rates from 6 sources.

[3] To learn more about Project Drawdown’s three growth scenarios, click the Scenarios link below. For information on Land Use Sector-specific scenarios, click the Sector Summary: Food link.

[4] For more on Project Drawdown’s Land Use integration model, click the Sector Summary: Food link below.