Long-term success of the Paris Agreement will depend on the effectiveness of the instruments that it sets in place. Key among these are the nationally determined contributions (NDCs), which elaborate country-specific goals for mitigating and adapting to climate change. One role of the academic community and civil society in supporting the Paris Agreement is to assess the consistency between the near-term action under NDCs and the agreement's long-term goals, thereby providing insight into the chances of long-term success. Here we assess the strengths and weaknesses of current methods to estimate the effectiveness of the mitigation component of NDCs and identify the scientific and political advances that could be made to improve confidence in evaluating NDCs against the long-term goals. Specifically, we highlight (1) the influence of post-2030 assumptions on estimated 21st century warming, (2) uncertainties arising from the lack of published integrated assessment modeling scenarios with long-term, moderate effort reflecting a continuation of the current political situation, and (3) challenges in using a carbon budget approach. We further identify aspects that can be improved in the coming years: clearer communication regarding the meaning, likelihood, and timeframe of NDC consistent warming estimates; additional modeling of long-term, moderate action scenarios; and the identification of metrics for assessing progress that are not based solely on emissions, such as infrastructure investment, energy demand, or installed power capacity. Plain Language Summary Under the Paris Agreement, all countries came together to strengthen their commitment to limit warming to well below 2 degrees C and established an aim toward 1.5 degrees C. Each country also presented its own climate action plan, including a description of how it intends to reduce its greenhouse gas emissions. A major challenge of the Paris Agreement is ensuring that, when combined, the individual actions of countries are sufficient to achieve the collective long-term goals. In this study, we review the methods used so far to evaluate the sufficiency of the climate action plans and examine how those methods can be improved. A significant difference between current methods is in the assumption of how countries' efforts to reduce emissions will change after the current timeframe of planned action (until 2030)-will it be weaker, stronger, or similar? Some methods are more complex and help to identify opportunities for additional action, while others are better at providing a quick estimate of the warming we can currently expect. We conclude that combining some of the methods we reviewed, modeling of scenarios similar to the current situation, and some clarification in communication would provide a better assessment of collective progress toward the Paris Agreement goals.
Jeffery, ML; Gütschow, J; Rocha, MR; Gieseke, R
Measuring Success: Improving Assessments of Aggregate Greenhouse Gas Emissions Reduction Goals
Earths Future