Highest possible ambition: an introductory guide to the assessment of national climate plans under Article 4.3 of the Paris Agreement

The Paris Agreement requires countries to formulate Nationally Determined Contributions (NDCs) towards reaching the global temperature goal of limiting warming well below 2°C while pursuing efforts to limit it to 1.5°C relative to pre-industrial levels. At present, countries’ emission reduction plans fall collectively short of what is required to meet this goal. Ensuring that forthcoming NDCs reflect countries’ ‘highest possible ambition’, as expected under the Paris Agreement, is therefore essential. This briefing introduces a new framework designed to translate the legal expectation of ‘highest possible ambition’ into a practical, evidence-based approach for both designing and assessing national climate pledges.