The rating methodology applied for international aviation and shipping policies is different from the CAT nationally determined contribution (NDC) “fair share” rating system. “Fair share” effort-sharing principles cannot easily be applied to sectors such as international aviation and shipping. To do so would require the attribution of GHG emissions from these sectors to countries, for which so far these is not a consensus. Therefore, we have developed a new methodology to determine a Paris Agreement-compatible emissions pathway for international aviation and the sector’s climate targets and policies.
To rate the international shipping and international aviation sectors we start out with the observation that to achieve the Paris Agreement’s temperature goal, global CO2 emissions need to reach net-zero around mid-century (IPCC, 2018). If these sectors decarbonise later than mid-century, other sectors would need to reach net-zero carbon emissions sooner, and/or deployment of corresponding negative emission technologies will be needed. To reflect that different sectors should share the decarbonisation burden, we applied the principle that international shipping and aviation should decarbonise at the same average rate as emissions from energy and industrial processes, thereby taking a comparable share of emissions efforts. This implies these sectors (together with all emissions from energy and industrial processes) should reach zero CO2 emissions by around 2060.
For this assessment, we have taken the global CO2 emission pathways for energy and industrial processes that are provided for by Integrated Assessment Models (IAMs) and assessed in the IPCCSR1.5. We filtered these pathways to exclude those that exceed sustainability limits for Bioenergy with Carbon Capture and Storage (BECCS) and Agriculture, Forestry and Other Land Use (AFOLU), as defined in the IPCC SR1.5. This gave us 19 scenarios that are consistent with the Paris Agreement and that we define as “CAT Filtered Pathways” (Yanguas Parra et al., 2019). This is the same filtering approach that we used for developing the domestic action and fair share ratings used in individual country assessments.
We have also extracted pathways that lead to a temperature increase between 1.5˚C-2˚C; between 2˚C-3 ˚C; between 3˚C-4˚C; and >4˚C from the IPCC IAM Database, so we have five sets of pathways that correspond to one temperature category each.
From each pathway set, we took the median emission levels between 2000 and 2100, with ten-year intervals. Using these median levels, we then calculated the annual growth rate for each temperature pathway and applied the growth rates to the historical average for the period of 2008-2018 for international shipping emissions. This approach differs slightly to that adopted for international aviation, where the growth rate was applied to emissions in the last historical year only and is due to the fact that emissions in that sector have increased steadily since 1990, whereas emissions from international shipping have fluctuated greatly.
This exercise supplied us with five temperature pathways, leading to global temperature increases ranging from 1.5˚C to over 4˚C compared to pre-industrial levels. We have assigned a rating to each of these temperature categories: 1.5˚C Paris Agreement compatible, 2˚C compatible, correspond to those temperatures, while the insufficient, highly insufficient, and critically insufficient ratings correspond to between 2˚C-3˚C; between 3˚C-4˚C; and >4˚C, respectively. While we use the same terms as for the individual country assessments, the definition of the ‘insufficient’ rating is different. For countries, these equates to the top of their fair share range, while for international shipping and aviation this rate equates to a temperature range.
The 1.5˚C pathway reflects the maximum level of international shipping emissions for the sector to be rated as ‘Paris compatible’.