This study investigates carbon sources and carbon sink estimation, nexus and validation through Land cover/ land use (LCLU) change analysis of Bangkok Metropolitan Area (BMA), Thailand. Considering spiking population and carbon emission trends, especially in metropolitan cities of developing countries, such estimations are direly needed. Moreover, quantification and empirical evidence involving such a multidisciplinary analysis are rarely available. Therefore, this study would help in understanding the relationship among economic development, carbon emissions, carbon sinks and land use change in BMA. CO2 emission and sequestration data from 1987 to 2015 were collected, and the changes and rate of change in LCLU were assessed by analyzing landsat satellite images of 1987, 1995, 2005, and 2015. Best efforts were put to attain net gains and losses in carbon sources and sinks analyses. Results showed that carbon sources have increased by almost 4-folds from 1987 to 2015 while sinks have declined rapidly to half of its original amount since 1987. The gap between carbon sources and sinks is widening year by year and will, if it continues in this manner, cover up the whole green space of BMA in the next decade. The LCLU change results also verified and showed the same results, which helped in validating such outcomes. Urban/built up area sprawl over 60% of BMA’s area while the remaining 40% constitutes agricultural land, green spaces, and water bodies. Furthermore, the rate of change of urban area was 157.4 sq km during 2005–2015 and 218 sq km during 1995–2005. Therefore, policy makers of BMA should seriously draft expansion plans of green spaces and public parks and implement it immediately to tackle with carbon emissions and land use change disquiets. Meanwhile, awareness regarding conservation of green areas, trees, and use of public transport could be another set of bottom-up policies.