In this study, the GHG emissions were calculated from 2000 to 2021 by focusing on the amount of disposal waste (or non-recyclables) in MSW treated by incineration in Seoul. The trend of GHG by incineration has continued to increase over time. The GHG emissions in 2021 were more than 7.3 times higher than those in 2000. The increase in GHG emissions is largely due to an increase in the amount of MSWI, especially plastic waste. Plastic waste consisted of 25% of MSWI, but the GHG emissions accounted for 92% of the total. For 2040, the amount of MSWI was 1676 tons/day, and GHG emissions were 389 kt CO2 eq/yr, all of which decreased by 53% compared to the BAU scenario. This might be attributed to reducing MSW generation and increasing recycling rates, resulting in reduced GHG emissions. Net GHG emissions from MSWI have been increasing since 2005, with an increase of 2.9 times in 2021 compared to 2005. All scenarios' net GHG emissions showed positive values, as the GHG emissions were greater than the GHG reductions.It is expected that GHG emissions in 2050 will be about 12.0 Tg CO2eq, which is 17% less than those in 2010.In order to reduce GHG emissions from MSWI, the first viable option is to reduce the MSW generation by households by implementing more strengthened measures (e.g., disposal fee increase, incentives for consumers to reuse). The second option is to establish material recovery facilities for resource recovery by diverting the waste from landfilling andincineration. During the recovery processes, plastic materials and other recyclable materials can be recovered for recycling. In the long term, GHG emissions could be reduced if CO2 from incineration is captured through CCUS (Carbon Capture Utilization and Storage) technology in the future, along with technical developments.It is expected that Seoul's MSWI will increase over the next few years. In particular, increased plastic consumption in households may be inevitable, resulting in an increase in GHG emissions by incineration if plastics are not reduced and recycled Thus, it is urgent for actions and measures to reduce the plastic waste in MSWI in Seoul by considering the adoption of a landfill ban policy by 2026. The results of this study can be used as climate change mitigation measures and responses for reducing GHG emissions from waste sectors in Seoul and other megacities in many countries.By utilizing the methane emission indicators prepared here and analyzing spatial correlations at a high resolution of 10 km, we found distinct differences in the sources of higher methane concentrations in terms of their distributions in South Korea: (1) fossil fuel use and landfill sites and (2) rice farming, and livestock areas with some regions with multiple emissions. Furthermore, the application of refined national statistical data in examining spatial correlations with satellite observations has been instrumental in identifying the causes of elevated methane concentrations in various areas. This approach holds significant potential to contribute to the enhancement of South Korea's official methane emission inventory, which currently does not have detailed spatial information, also addressing challenges that global methane inventories cannot resolve.Finally, the spatial correlation analysis with satellite data conducted in this study proves highly useful in understanding and validating national methane emission information. This is particularly beneficial in cases like Korea, where spatial information on methane emissions is limited or where there is a high likelihood of unidentified emission sources.