Reducing greenhouse gas emissions from aviation: “timing is everything”

In the run up to the triennial Assembly of the UN International Civil Aviation Organization, where climate change is positioned as a significant item on the agenda, scientists from the Centre for Aviation Transport and the Environment at Manchester Metropolitan University (UK) have published a science-based report on the best and most cost-effective way of mitigating future aviation emissions. Although aviation is responsible for only about 2% of global greenhouse gas emissions, the sector is frequently a target of criticism, in part because it is seen to have among the highest emissions per passenger-km and because it appears to be a rapidly growing sector.

The report analysed 23 incremental mitigation scenarios for aviation CO2 emissions for their reductions in radiative forcing/temperature response by 2050 over a business as usual (BAU) aviation technology/operational improvements scenario. The mitigation measures included five levels of technology/operational improvements, three levels of biofuel market penetration, and two levels of geographical coverage of an emissions trading system.

The research found that emissions trading, as designed by the European Union, would provide the largest single incremental improvement in radiative forcing and temperature response by 2050 of ~15% (range 12 to 17%) over BAU. The next largest single potential contributor, as a measure, to reductions in aviation CO2 radiative forcing by 2050, was a maximum feasible reductions scenario of reductions in aviation CO2 emissions from technological and operational improvements of 6.4% (range 6.1 to 6.9%). The additional introduction of “likely” levels of biofuels over BAU gave the smallest reduction, as a single measure, in aviation CO2 radiative forcing by 2050 over BAU of 1.1% (range 1.0 to 1.2%). By combining MFR technology/operational improvements with biofuels at “speculative” levels, reduced aviation CO2 radiative forcing over BAU by 9% (range 8.3 to 9.6%). Combining all possible measures – MFR technology/operations, “speculative” biofuels, and the EU-ETS, reduced aviation CO2 RF by 19.5% (range 16.1 to 21.5%) over BAU.

The researchers found that the reason that emissions trading schemes result in such marked radiative forcing reductions is their inherent ability to achieve emission reductions quickly, which is vital when considering the effectiveness of any CO2 mitigation action, because of the accumulative nature of CO2 in the atmosphere. The timing as to when reductions in CO2 emissions occur matters – not just the achievement of an emissions goal by some future date. The data show that early reductions in CO2 emissions produce the best environmental response.

The full paper, and a summary, are both available at 

The ICAO Assembly takes place in Montreal from 24 September to 4 October 2013.


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