This study focuses on estimating carbon stocks in Trenggalek's forest and coastal areas, assessing their contributions to carbon sequestration and climate change mitigation. The study was conducted in two phases. First, a field-based estimation of carbon stocks was carried out for both mangrove and plantation forests, with 72 sample plots (10m x 10m) laid out systematically. Above-ground biomass was calculated using an allometric model, while below-ground biomass was based on ratios of above-to-below ground biomass. Results showed that mangrove forests had an average carbon stock of 12.80, 23.45, and 76.15 tons/ha in above-ground biomass, below-ground biomass, and soil organic carbon, respectively, while plantation forests had higher values of 77.05, 114.2, and 75.76 tons/ha. The potential CO2 absorption also varied, with mangrove forests showing lower values due to their smaller biomass compared to plantation forests, though the mangroves had higher soil organic carbon storage. In parallel, the study evaluated the carbon uptake potential of coastal waters in Trenggalek Regency, based on primary productivity from phytoplankton. Sampling was done purposively, and carbon sequestration potential was calculated using the dark-light bottle method. The waters exhibited a mesotrophic state with primary productivity values ranging from 150-950 mgC/m³/day. The carbon uptake potential varied across stations from 3.69 to 23.35 tonsC/m²/year, indicating that coastal waters in Trenggalek Regency acts as a carbon sink, driven by a positive net primary productivity (NPP). Additionally, remote sensing techniques were used to analyze changes in land cover and carbon stock in Trenggalek’s coastal areas over time, using temporal Landsat data and Google Earth Engine. From 2001 to 2023, the carbon stock declined from 4,126,833.64 tons to 3,769,725.32 tons, but a slight increase is predicted by 2034 to 3,778,537.21 tons. These findings highlight the importance of field data in accurately predicting future carbon stock estimates, enhancing the understanding of forest and marine ecosystems roles in climate change mitigation and the importance of sustainable land use management to preserve carbon stock potential in Trenggalek’s ecosystems