The report by Manchester Metropolitan University’s Centre for Air Transport and Environment (CATE) “Mitigating future aviation CO2 emissions – timing is everything” shows that the real climate benefit of any action depends on the cumulative emission reductions between now and a future date, and not just on achieving a certain amount of emission reductions by a specific year (as ICAO has focused on): CO2 has a long lifetime so concentration levels are determined by cumulative emissions over time. Early reductions result in a lower emissions trajectory than equivalent annual savings made at a later date.
The report shows that while the technology, operations and alternative fuels measures that are ICAO’s focus have the potential to make significant reductions in the climate impact of emissions from aviation, these will only come in the longer term given the lead times needed to develop and bring to market whereas immediate reductions from effective market based measures implemented now far outweigh the climate impacts of ICAO’s approach.
The report shows that a global MBM such as emissions trading introduced in 2012 and the existing European Emissions Trading Scheme (EU-ETS) for aviation provide the largest single incremental improvements in radiative forcing (RF)  and temperature response by 2050 (a 30.1% improvement in RF for a global MBM and around 15% in RF for the EU ETS compared to a business as usual scenario based on technology and operational improvements). Based on best estimates of likely future uptake, biofuels would have a minimal climate impact by 2050.
Commenting on the report’s conclusions Bill Hemmings of T&E said: “This robust analysis is compelling and should be a wake-up call to States and industry as they prepare for ICAO’s Assembly. ICAO’s traditional approach focussing on technology, operations and biofuels falls far short of what is needed.”
Meanwhile, Tim Johnson of NGO Aviation Environment Federation (AEF) said: “ICAO has already demonstrated that its own modest goal of carbon neutral growth by 2020 will be impossible to achieve without market-based measures, while the scale of reductions required to contribute towards a 2 degree pathway reinforces that argument unequivocally. It’s time to stop debating the ‘if’ and focus on the ‘how’.”
Fig. 1: Effect of mitigation options on CO2 radiative forcing to 2050 attributable to international aviation (source MMU, 2013)
Fig. 2: CO2 radiative forcing savings for international aviation from business-as-usual (BAU) technology and operations improvements in combination with different mitigation options, compared with the business-as-usual (BAU) scenario (source MMU, 2013)