Apportioning aviation CO2 emissions to regional administrations for monitoring and target setting

The aim of this paper is to provide an overview of the different CO2 allocation options that can be used to divide emissions from aviation between sub-national administrative areas. Emissions from aviation, both domestic and international, represent a growing proportion of the UK’s CO2 emissions, yet only domestic aviation emissions are included in UK’s emission reduction targets and even these emissions are rarely included in the inventories and reduction strategies of sub national administrations. At present there is not a widely accepted method of how emissions from both international and domestic aviation should be fairly attributed between countries and sub- national areas. One reason for this is that airports often serve customers from countries and areas other than their locality. This is compounded by the stance often taken by administrative bodies that emissions from aviation is ‘outside’ of their control and is a matter for ‘international’ agreement rather than national or sub-national action. While not accepting any level of responsibility for the emissions, the same bodies often provide economic support for airport (and thus aviation) development and expansion as well as aerospace manufacturers with the argument that aviation is integral to the continuing economic development of the area and nation as a whole. One of the principles behind the carbon budgeting approach proposed to deliver atmospheric stabilisation of CO2 equivalence at a level to avoid dangerous climate change is that all sources of greenhouse gas emissions must be included in the budget. Therefore, omitting (growing) aviation emissions from any budget will inevitably lead to budget overspend and thus miss the target for atmospheric stabilisation and the avoidance of dangerous climate change. It is important therefore to ensure that all aviation emissions are allocated between sub-national (and national) administrations for budgeting purposes. The administration is then able to fully appreciate the emission reductions necessary to meet their agreed targets, offsetting growth in aviation emissions with savings from other sectors if necessary. There are a number of methodologies proposed for the allocation of international aviation emissions to countries8; this study assesses their suitability for allocating both domestic and international aviation emissions to sub-national areas. The paper provides the data implications, advantages and disadvantages of each method and suggests practical developments for use at a sub-national scale. The allocation methods can be used firstly as a baseline to assess the contribution of aviation to the region’s carbon footprint, to design cross-sectoral greenhouse gas mitigation strategies and to monitor the success of future methods which seek to mitigate growth in CO2 emissions taken international, national and sub-national levels.