Accurately estimating historical emissions from mangrove deforestation both establishes emissions baselines upon which greenhouse gas mitigation commitments are based and bounds the potential for mangrove restoration to mitigate climate change. However, quantifying historical emissions is often limited by data availability. Here, we exemplify a process of quantifying historical net carbon flux from changes in mangrove extent for Thailand. Thailand currently has the 11th largest extent of mangroves globally, but is estimated to have had over double that extent before 1960. We quantified net emissions from mangrove loss in Thailand by coupling modeled estimates of carbon stocks for intact, deforested, and restored mangroves with estimates of mangrove extent from both government statistics and remotely sensed datasets. Combining the government statistics and remotely sensed data allowed us to estimate mangrove loss from decades before the availability of remotely sensed data. In addition to the carbon flux estimates, we performed a sensitivity analysis to identify key factors in estimating emissions from mangrove loss at national scales.
Results/Conclusions
We estimated total potential emissions from loss of mangroves between 1961 and 1996 as 299,000 Gg CO2e (8,500 Gg CO2e yr-1), and approximately 19,900 Gg CO2e (995 Gg CO2e yr-1) from 1996 to 2016. We assumed total loss of aboveground biomass and soil organic carbon (SOC) in the top meter of soil given the near-complete conversion of mangroves to aquaculture. We elected to use estimates of mangrove extent derived from remotely sensed data over government statistics given large differences in the two estimates and greater transparency in the methods used to produce the remotely sensed data numbers. From 1996 to 2016, we estimated sequestration of 900 Gg CO2e (45 Gg CO2e yr-1) from mangrove gain for a net change of 19,000 Gg CO2e (950 Gg CO2e yr-1) during this time period. Importantly, we did not include the recovery of the SOC pool with mangrove gain as sequestration of SOC is currently poorly constrained. The World Bank estimated Thailand’s total CO2e emissions at 281,000 Gg in 2018, suggesting that recent annual mangrove loss makes up just 0.35% of Thailand’s annual emissions and mangrove gain sequesters only 0.02% of annual emissions. The findings are highly sensitive to assumptions regarding the SOC pool, suggesting the need for better conceptual models of SOC emissions from land use change as well as additional research to better constrain SOC sequestration from mangrove restoration.