Abstract
Mangroves are important sinks of organic carbon (C) and there is significant interest in their use for greenhouse gas emissions mitigation. Adverse impacts on organic carbon storage potential from future climate change and deforestation would devalue such ambitions, thus global projections of future change remains a priority research area. We modeled the effects of climate change on future C stocks and soil sequestration rates (CSR) under two climate scenarios (“business as usual”: SSP245 and high-emissions: SSP585). Model results were contrasted with CO2 equivalents (CO2e) emissions from past, present and future rates of deforestation on a country specific scale. For C stocks, we found climate change will increase global stocks by ∼7% under both climate scenarios and that this gain will exceed losses from deforestation by the end of the twenty-first century, largely due to shifts in rainfall. Major mangrove-holding countries Indonesia, Malaysia, Cuba, and Nigeria will increase national C stocks by > 10%. Under the high-end scenario, while a net global increase is still expected, elevated temperatures and wider temperature ranges are likely increase the risk of countries’ C stocks diminishing. For CSR, there will likely be a global reduction under both climate change scenarios: 12 of the top 20 mangrove-rich countries will see a drop in CSR. Modeling of published country level mangrove deforestation rates showed emissions have decreased from 141.4 to 6.4% of annual CSR since the 1980’s. Projecting current mangrove deforestation rates into the future resulted in a total of 678.50 ± 151.32 Tg CO2e emitted from 2012 to 2095. Reducing mangrove deforestation rates further would elevate the carbon benefit from climate change by 55–61%, to make the proposition of offsetting emissions through mangrove protection and restoration more attractive. These results demonstrate the positive benefits of mangrove conservation on national carbon budgets, and we identify the nations where incorporating mangrove conservation into their Nationally Defined Contributions offers a particularly rewarding route toward meeting their Glasgow Agreement commitments.
Highlights
Mangroves, tidal marshes and seagrass meadows accumulate organic rich soils that can often extend to many meters depth and provide long-term storage of organic carbon (C)
The literature search resulted in 785 data points of soil C100 stocks from 87 individual studies conducted in 44 countries and 105 data points of soil C sequestration rates (CSR) from 31 individual studies in 17 countries (Supplementary Datasets 1, 2)
Predicted climate change in Mainland Southeast Asia and southern Brazil resulted in lower C stocks, whilst higher C stocks were predicted in the Caribbean, the Malay Archipelago, Australia, and West and East Africa (Supplementary Figure 2)
Summary
Tidal marshes and seagrass meadows accumulate organic rich soils that can often extend to many meters depth and provide long-term storage of organic carbon (C). Mangroves store up to five times as much organic carbon as tropical upland forests (Donato et al, 2011). A combination of high productivity and slow soil decomposition rates significantly increases mangroves’ ability to capture and store organic carbon, in their soils (Alongi, 2012). Aboveground net primary productivity (NPP) rates in mangroves (8.1 t DW ha−1 yr−1) rival those of highly productive tropical terrestrial forests (11.1 t DW ha−1 yr−1) (Alongi, 2012). Mangroves have received a great deal of scientific interest as natural systems for offsetting greenhouse gas (GHG) emissions (Donato et al, 2011; Fourqurean et al, 2012)
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