In particular, this paper addresses the energy and economic impacts of the possible range of carbon constraints in Southeast Asian countries by addressing two dimensions of the uncertainty of carbon reduction targets: Annex I reduction targets and required global CO2 levels to stabilize 2 °C goal. The gaps between Annex I contribution and global limits are fulfilled by accessions of non- Annex I countries in 2020 with differentiated responsibilities between LDCs and non-LDCs.