“Government airbrushes aviation’s non-CO2 greenhouse gas emissions” – new report
It been recognised for many years that the climate change impacts of aviation extend well beyond those of carbon dioxide (CO2), due to jet fuel being burned at high altitude, creating a range of impacts – including formation of cirrus cloud from contrails. But this fact is largely ignored by the government and its agencies. A new report, produced for AirportWatch, examines the reasons for this and proposes an ‘index’ which will help to ensure that the issue of non-CO2 gases is properly accounted for. Though DECC continues to use a multiplier of 1.9 for the CO2 alone, in its conversion factors, the issue of the non-CO2 impacts has been systematically downplayed by the UK government and its associates over recent years. While ‘scientific uncertainty’ is claimed as the reason to ignore non-CO2, the report considers the real reason is that aviation emissions are an embarrassment to government and others who want to expand airports and air travel. The new paper suggests a new index should be developed. To be very conservative, this should be set at a multiplier of 1.6 of the CO2 emissions alone. It would be an interim measure, pending a thorough and independent review of the issue of aviation’s non-CO2 emissions. Ignoring the non-CO2 impacts of aviation, due to scientific uncertainty, is not acceptable. Using lack of certainty as a justification for ignoring a known issue would not be accepted in other areas.
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“Government airbrushes aviation’s non-CO2 greenhouse gas emissions”
By Nic Ferriday, for AirportWatch
June 2015
1. Introduction
While it been recognised for many years that the climate change impacts of aviation extend well beyond those of carbon dioxide (CO2), this fact is largely ignored by the government and its agencies. Our report examines the reasons for this and proposes an ‘index’ which will help to ensure that the issue of non-CO2 gases is properly accounted for.
2. Executive summary
In recent years there has been systematic downplaying of the issue of non-CO2 gases by the UK government and its associates. This report provides the evidence for that claim.
While ‘scientific uncertainty’ is claimed as the reason to ignore non-CO2, the real reason is that aviation emissions are an embarrassment to government and others who want to expand airports and air travel.
In earlier governmental and academic studies a ‘Radiative Forcing Index’ (RFI) has been used in order to capture non-CO2 impacts. However, RFI is a ‘backward looking metric’ and is therefore considered unsuitable for informing aviation policy.
This report argues that instead of just dropping the previously used RFI, it should be replaced by a ‘Global Warming Potential’ (GWP) index for estimating impacts and developing policy responses.
A rough value for the index of 1.6 is estimated. CO2 emissions should be multiplied by 1.6 in order to allow for the impact on non-CO2 GHGs. This is a very conservative figure – the true figure could be much higher, due mainly to cirrus.
The estimate and calculations around it are very approximate. The factor of 1.6 should therefore be regarded very much as an interim, pending a thorough and independent review of the issue of aviation’s non-CO2 emissions.
Although the proposed index is approximate and interim, it should be used forthwith in order to demonstrate impacts and inform policy. Citing scientific uncertainly as a justification for ignoring an issue would not be acceptable in other fields of public policy and should not be accepted when it comes to aviation emissions.
AirportWatch Briefing on Radiative Forcing June 2015
11. Discussion
The material presented above gives clear evidence of a progressive downplaying of the impacts of aviation’s non-CO emissions by DfT, CCC and latterly AC. Their documents recognise that non-CO2 emissions are significant but then simply ignore them or give excuses for ignoring them.
There seem to be two main arguments given for ignoring non-CO2 GHGs. Firstly that RFI is an inappropriate metric. Secondly, that the science is uncertain. We examine these below.
It is argued by Lee and others that the use of RFI is inappropriate because it is a ‘backward-looking’ metric. It tends to over-emphasise the impacts of non-CO2 gases because the residence time of those gases is less than CO2. That RFI is a backward-looking metric and that some ‘forward-looking’ metric is better is common ground. However, this recognition is nothing new and so does not explain the progressive downplaying of non-CO2 emissions.
Other forward-looking metrics, notably GWP, have been proposed. GTP has also been proposed but, as explained in app 1, we consider the use of GTP inappropriate because it ignores all climate impacts and costs up to the year in which it applies, eg 100 years hence.
While GWP may not be ideal, it is the best there is at present. It therefore makes sense to use it when assessing impacts and developing policy. This principle extends to all area of scientific research and public policy. In our real and imperfect world we have to use the best evidence and the best estimates that are available. To argue that because our knowledge is imperfect, we should ignore an issue is absurd. Such an argument is not applied in other areas of public life. Uncertainly about future terrorist attacks or Ebola outbreaks is not used as a reason to ignore the issues.
The real reason for airbrushing non-CO2 emissions is not hard to find. There is increasing pressure on and from politicians to expand airports and air travel. The climate impacts of such a policy represent a highly ‘inconvenient truth’. Given the widespread recognition of the role of CO2, government and its agencies could not hope to ignore CO2 impacts without attracting the severest criticism. But for non-CO2 emissions, about which there is as yet very little public knowledge, government and its servants can hope to ignore the impacts while escaping criticism.
Global Warming Potential (GWP) is noted in the literature as a promising metric. However a period need to be defined over which the effect are integrated. We argue in app 7 that an average of GWP35 and GWP100 should be used.
Including cirrus, GWP35 and GWP100 are 3.69 and 1.9 respectively, giving an average of 2.8. However, the uncertainty around cirrus is especially large. This, leading to possibly misleading high impacts, makes a case for omitting cirrus from an index at present.
Excluding cirrus, GWP35 and GWP100 are 1.92 and 1.4 respectively, giving an average of 1.61, rounded to 1.6. This is a very conservative figure – that is, it is likely to be lower than the true values. (It is conservative because cirrus, although subject to great uncertainty, is nonetheless expected with a fair degree of confidence to add significant radiative forcing. The calculations also assume a ‘low’ inpact of NOx.)
Where there are significant uncertainties, it seems appropriate to use conservative values. This will avoid ‘overshoot’ whereby a high index is initially selected, leading to a particular set of policy responses, only for the index to be reduced in the light of further research, leading to possible differences or even reversals of policy responses.
Based on the foregoing, we propose an index of 1.6, based on GWP calculations. That is, impacts of CO2 alone should be multiplied by 1.6 to allow for non-CO2 impacts. This factor should be applied forthwith in order to inform the debate on the impacts of aviation and policy responses to it.
The data and calculations supporting this are indeed approximate, but there is very strong evidence that non-CO2 impacts are significant. Furthermore, the factor of 1.6 is very conservative. These are compelling reasons to allow for non-CO2 emissions and to apply this factor. Simply citing ‘scientific uncertainty’ as a reason for ignoring non-CO2 emissions and not applying any factor is not tenable.
Recognising the ‘rough and ready’ nature of the calculations, the proposed index of 1.6 should be regarded very much as an interim figure. A proper and fully independent study should be undertaken in order to refine this index or, indeed, to devise an alternative approach for addressing non-CO2 impacts.
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The report:
AirportWatch Briefing on Radiative Forcing June 2015
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