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This study first evaluates the pledges under the Copenhagen Accord using the DNE21+ model. Our estimates for the 2020 pledges fall collectively within the range of 46,700–49,100 Mt CO 2 -eq. Our study also finds the efforts arising from the current 2020 pledges have wide-ranging implications in terms of mitigation costs and types of actions. Based on this analysis, we seek to place the Copenhagen pledges in a long-term context, putting focus on costs and feasibility. We set up a “Carbon Prices Convergence Scenario,” assuming that all countries start from the Copenhagen commitments and gradually undertake their own individual efforts in accordance with the convergence of carbon prices toward a uniform price in 2050. Despite soaring carbon prices in most countries, total costs as share of GDP show modest increase, ranging mostly between 0% and 0.4%. We also find that there does not seem to be much difference in the degree of burden between developed and major developing countries under this scenario. Since the challenge of climate change will require significant reductions in GHG emissions in the coming decades, we need to make long lasting efforts, getting on the right track toward the ultimate goal of stabilizing GHGs.