Midway toward the 2 degree target: Adequacy and fairness of the Cancْn pledges

Many countries pledged to reduce their greenhouse gas emissions by 2020 during the 2009 Copenhagen Accord and the 2010 Cancún Agreement. This paper evaluates the Cancún pledges from two aspects, namely, temperature increase and carbon Gini coefficient. The Model for the Assessment of Greenhouse-gas Induced Climate Change is used to calculate the temperature increase, and the carbon Gini coefficient is used to measure the equivalence of emission–reduction allocations. We first downscale regional business as usual (BAU) scenarios from integrated assessment models to the national level. Then, we combine the downscaled BAU with Cancún pledges to generate the emission trajectory of the pledges. We use emissions with and without pledges as input to assess the adequacy and fairness of the pledges by using temperature increase and carbon Gini coefficient, respectively. Based on the results, we show that the Cancún pledges would reduce the temperature increase to a great extent, but not enough to meet the 2 degree target. Due to the insufficient contribution from developed countries, the Cancún pledges will sacrifice equity among countries, especially between developed and developing countries. The common understanding of equity will be essential to bridge the mitigation gap toward meeting the 2 degree target.