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.
Indirect CO2 emissions caused by the fuel demand switch in international shipping