Technical Summary

Coastal Wetland Restoration

Project Drawdown defines coastal wetland restoration as: “any process that aims to return a system to a pre-existing condition (whether or not this was pristine) (sensu Lewis, 1990c)” including both “natural restoration” or anthropogenic- led recovery (Lewis, 2005) of carbon-rich mangroves, seagrasses, and saltmarshes. This solution recovers coastal wetlands ecosystems capacity as carbon sinks.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 restoration solution proposes increased restoration 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 7.32 million hectares, while current adoption was set to 0.

Adoption Scenarios[2]

Six custom adoption scenarios were developed for each of these three coastal wetlands using a linear growth curve based on the Guatemala’s National Restoration Strategy which aims to restore 10,000 hectares on mangroves between 2015 and 2045 and Green India Mission which included a commitment to restore 100,000 hectares of mangroves between 2010 and 2020. In the absence of similar information for the seagrasses and saltmarshes, the adoption of these coastal wetlands are projected based on mangroves growth rate which is applied to their respective total land area and degradation rate. Given the small area of coastal wetlands, and the high mitigation efficiency of restoration, some scenarios emphasized early peak adoption by 2030.

Impacts of increased adoption of coastal wetland restoration 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 6.07million 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 7.24 million hectares of unprotected coastal wetlands.

Emissions, Sequestration, and Yield Model

Sequestration rates for mangroves are set at 6.58 tons of carbon per hectare per year, based on meta-analysis of 27 data points from 13 sources. Salt marsh sequestration rates are 0.93 tons of carbon per hectare per year, based on 15 data points from 6 sources. Seagrass sequestration is set at 0.99 tons of carbon per hectare per year, based on 16 data points from 4sources.

Financial Model

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

Integration[3]

The coastal wetland restoration 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 6.07 million hectares in 2050, representing 83 percent of the total available land. Of this, 6.07 million hectares are adopted from 2020-2050. The emissions impact of this scenario is 0.99 gigatons of carbon dioxide-equivalent reduced by 2050. Financial impacts are not modeled.

Total adoption in the Scenario 2 is 7.24 million hectares in 2050, representing 99 percent of the total available land. Of this, 7.24 million hectares are adopted from 2020-2050. The impact of this scenario is 1.01 gigatons of carbon dioxide-equivalent by 2050.

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] 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.

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