# Impacts of Climate Change on Blue Carbon Stocks and Fluxes in Mangrove Forests
## 3 Climate Change Impacts
### Sea-Level Rise (SLR)
Warm temperatures and SLR are driving latitudinal expansion of mangroves into salt marsh habitat in subtropical and tropical areas. Studies have indicated that the invasion of mangroves into previously dominated marsh habitat has resulted in greater soil carbon concentrations and blue carbon accumulation in the newly colonized mangroves [55; 56]. Further, on the American east coast slowly rising seas since the mid-Holocene promoted 2-4 times greater soil carbon stocks in mangroves in America than in Australia where sea-level fall resulted in sufficient time for carbon to exit the ecosystem through decomposition and tidal export pathways [56]. These forecasts of course ignore the reality of high spatial and temporal variability in SLR and subsequent mangrove responses, even at the local scale, which will have large  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{1}{c}{**Year**} & \multicolumn{3}{c}{**(A) CO2 Emissions Scenarios**} \\ \multicolumn{1}{c}{**Intervals**} & & & \\ \hline  & **Very low** & **Low** & **Intermediate** & **High** & **Very High** \\ \hline
2040–2060 & **4.2 (2.9–6.1)** & **4.9 (3.6–6.9)** & **5.9 (4.5–8.0)** & 6.5 (5.1–8.7) & 7.3 (5.7–9.8) \\ \hline
2080–2100 & **4.3 (2.5–6.6)** & **5.3 (3.3–8.1)** & 7.8 (5.3–11.5) & 10.4 (7.5–14.9) & 12 (8.8–17.7) \\ \hline  & & & & \\ \hline  & & & & \\ \hline  & & & & \\ \hline  & & & & \\ \hline  & & & & \\ \hline  & & & & \\ \hline  & & & & \\ \hline  & & & & \\ \hline  & & & & \\ \hline  & & & & \\ \hline  & & & & \\ \hline  & & & & \\ \hline  & & & & \\ \hline  & & & & \\ \hline  & & & & \\ \hline  & & & & \\ \hline  & & & & \\ \hline  & & & \\ \hline  & & & & \\ \hline  & & & & \\ \hline  & & & \\ \hline  & & & \\ \hline  & & & & \\ \hline  & &implications for mangrove survival and carbon cycling. A good example is an examination of mangrove species' responses to SLR across the island of Pohnpei, Federated States of Micronesia [57]. A modeling study was conducted using empirical data of soil elevation, accretion rates, forest inventories, water-level monitoring, and differential leveling elevation surveys, to identify which regions and mangrove communities are most vulnerable to SLR. Responses of mean elevation and community composition were analyzed under four SLR scenarios (37, 52, 67, or 117 cm by 2100). The model projected mangrove survival relative to the 37 and 52 cm scenarios with limited relative increases in more flood-tolerant species through 2060. The most flood-tolerant species, _Sonneratia alba_ and _Rhizophora stylosa_, will increase in relative dominance for 30-40 years before declining, whereas _Bruguiera gymnorhiza_, _Xylocarpus granatum_, and _Rhizophora apiculata_ will in most scenarios decline [57]. Given known species differences in carbon balance and metabolism, and soil carbon concentrations and rates of carbon cycling [6], such changes presage significant differences in mangrove carbon dynamics with SLR. Both the rate of CO\({}_{2}\) emissions and the level of accommodation space has been used to measure the impact of SLR on mangrove blue carbon stocks and emissions [58]. Using projected changes in global mangrove areas, global mean carbon stocks and rates of carbon sequestration, the RCP8.5 scenario, where SLR by 2100 is projected between 0.5 and 1.0 m, could result in net gains in blue carbon on the order of 1.5 Pg C to 2100 (Figure 1A), but only under low 'coastal squeeze'. Low 'coastal squeeze' is a high adaptation scenario where mangroves can occupy available space when population density thresholds are between 150 and 300 people km\({}^{-2}\) (called P300). Under a high 'coastal squeeze' scenario (low adaptation scenario where landward migration is prevented as population densities exceed a threshold of 5-20 people km\({}^{-2}\) (called P5)), losses of mangrove blue carbon are expected, resulting in CO\({}_{2}\) emissions in the range of 3.4 Pg C to 2100 (Figure 1B).