Climate benefits of proposed carbon dioxide mitigation strategies for international shipping and aviation

Abstract

While individual countries work to achieve and strengthen their nationally determined contributions (NDCs) to the Paris Agreement, the growing emissions from two economic sectors remain largely outside most countries' NDCs: international shipping and international aviation. Reducing emissions from these sectors is particularly challenging because the adoption of any policies and targets requires the agreement of a large number of countries. However, the International Maritime Organization (IMO) and the International Civil Aviation Organization (ICAO) have recently announced strategies to reduce carbon dioxide (CO2) emissions from their respective sectors. Here we provide information on the climate benefits of these proposed measures, along with related potential measures. Given that the global average temperature has already risen 1 ∘C above preindustrial levels, there is only 1.0 or 0.5 ∘C of additional “allowable warming” left to stabilize below the 2 or 1.5 ∘C thresholds, respectively. We find that if no actions are taken, CO2 emissions from international shipping and aviation may contribute roughly equally to an additional combined 0.12 ∘C to global temperature rise by end of century – which is 12 % and 24 % of the allowable warming we have left to stay below the 2 or 1.5 ∘C thresholds (1.0 and 0.5 ∘C), respectively. However, stringent mitigation measures may avoid over 85 % of this projected future warming from the CO2 emissions from each sector. Quantifying the climate benefits of proposed mitigation pathways is critical as international organizations work to develop and meet long-term targets.