Future carbon emissions from global mangrove forest loss

Abstract

Mangroves have among the highest carbon densities of any tropical forest. These 'blue carbon' ecosystems can store large amounts of carbon for long periods, and their protection reduces greenhouse gas emissions and supports climate change mitigation. Incorporating mangroves into Nationally Determined Contributions to the Paris Agreement and their valuation on carbon markets requires predicting how the management of different land-uses can prevent future greenhouse gas emissions and increase CO₂ sequestration. We integrated comprehensive global datasets for carbon stocks, mangrove distribution, deforestation rates, and land-use change drivers into a predictive model of mangrove carbon emissions. We project emissions and foregone soil carbon sequestration potential under 'business as usual' rates of mangrove loss. Emissions from mangrove loss could reach 2391 Tg CO_{2 eq} by the end of the century, or 3392 Tg CO_{2 eq} when considering foregone soil carbon sequestration. The highest emissions were predicted in southeast and south Asia (West Coral Triangle, Sunda Shelf, and the Bay of Bengal) due to conversion to aquaculture or agriculture, followed by the Caribbean (Tropical Northwest Atlantic) due to clearing and erosion, and the Andaman coast (West Myanmar) and north Brazil due to erosion. Together, these six regions accounted for 90% of the total potential CO_{2 eq} future emissions. Mangrove loss has been slowing, and global emissions could be more than halved if reduced loss rates remain in the future. Notably, the location of global emission hotspots was consistent with every dataset used to calculate deforestation rates or with alternative assumptions about carbon storage and emissions. Our results indicate the regions in need of policy actions to address emissions arising from mangrove loss and the drivers that could be managed to prevent them.

Keywords: Nationally Determined Contributions; blue carbon; carbon sequestration; climate change; coastal wetlands; erosion; greenhouse gases; tropical storms.

FIGURE 1

(a) Global projected CO_2 eq emissions (Tg) by the end of the century (2010–2100) for the marine provinces of the world and (b) the proximate driver responsible for the largest CO₂ emissions for each marine province (Goldberg et al., 2020). The names and location for all marine provinces can be found in Figure S1

FIGURE 2

Cumulative CO_2 eq emissions (Tg) by the end of the century (2010–2100) attributed to the proximate drivers of mangrove loss for the marine provinces ranked in the top ten for future CO₂ emissions

FIGURE 3

Emission reductions (Tg CO_2 eq) that could be achieved from (a) management of agriculture/aquaculture and shore stabilisation in the West Coral Triangle and (b) decrease in erosion through shore stabilisation, mangrove protection to avoid clearing and restoration of mangroves affected by tropical storms in the Tropical Northwest Atlantic

FIGURE 4

Sensitivity analyses comparing cumulative CO_2 eq emissions at the end of the century (2010–2100) using (a) soil organic carbon (SOC) modelled (1 and 2 m deep; Sanderman et al., 2018), SOC obtained in the field (Kauffman et al., 2020) and modelled aboveground biomass carbon (ABC; Simard et al., 2019) and obtained in the field for the 15 provinces with data (Kauffman et al., 2020); (b) comparison between emissions with mangrove area from Bunting et al. (2018) and Hamilton and Casey (2016) with SOC at 1 and 2 m, and with deforestation rates of Goldberg et al. (2020) and Hamilton and Casey (2016); (c) comparison of ranking among provinces with highest cumulative CO_2 eq emissions with and without accounting for emissions from climate events, and (d) with low (50%) and high (100%) emission factors from erosion