Climate researchers find even carbon-neutral growth from 2020 will not be enough to stave off climate impacts
Thu 3 Oct 2013 – As countries argue at the current ICAO Assembly over attempts to stabilise the growth in aviation carbon emissions, a new study from Manchester Metropolitan University (MMU) shows even this will not be enough to hold back climate impacts. The key aspirational carbon-neutral growth goal of ICAO, and supported by the aviation industry, is to maintain CO2 emissions at 2020 levels (CNG2020) but because the greenhouse gas has a very long lifetime, the overall effect is an increase in radiative forcing and temperatures. Only the industry goal of halving 2005 emissions by 2050 is more likely to keep climate impacts from aviation within the 2 degree goal, conclude the researchers. The study follows other recent MMU research that demonstrated market-based measures were required to meet the CNG2020 target and that action to implement them had to be taken quickly.
“It is vital that aviation reduces its CO2 emissions, along with all other sectors,” said Professor David Lee, Director of MMU’s Centre for Aviation, Transport and the Environment. “ICAO had promised at its last General Assembly three years ago to explore what this stabilisation of net international emissions at 2020 levels might mean in terms of impacts and how it might be achieved. However, there is very little progress on this, and it is an ‘ongoing action’ at this Assembly meeting.”
Lee’s research team looked at three potential growth scenarios of aviation CO2 emissions. Scenario 1 combined CNG2020 for international emissions with business-as-usual domestic aviation emissions (domestic emissions, forming 32% of the global total and not covered by ICAO); Scenario 2 combined CNG2020 for international emissions with maximum feasible reductions from technology and operations improvement plus biofuels; and Scenario 3 assumes CNG between 2020 and 2050 for both international and domestic aviation. Analysis was undertaken for the three growth scenarios and four background CO2 scenarios, totalling 1,920 simulations.
At a constant emissions rate, the researchers found radiative forcing – the metric used by climate scientists to measure climate impact – continues to increase for a constant emission rate since CO2 is accumulating much faster in the atmosphere than it is removed. For constant annual emissions at 2020 levels, the aviation CO2 radiative forcing increases by a factor of 1.6 in 2050 over 2020 values and by a factor of 2.5 by 2100 over 2020 values.
“If a tonne of CO2 is released, 30% is removed in a few decades, 50% is removed over a few centuries and the remaining 20% is only removed over millennia,” explained Lee. “So, stabilisation of emissions in the general scheme of things is not enough, and we know this from the science and have shown this in previous reports of the IPCC and UNEP.
“So physics is against us and dramatic reductions of overall global CO2 are needed in order to stabilise temperature increases by 2100. The question is what role is aviation going to play in that overall climate objective, and how?
“What we have done is provide a science-based assessment of the implications of the ICAO CNG goal and we hope this may provide some useful, if sobering, input to policymakers at this current ICAO Assembly.